fix #26 (backend,frontend): Frontend can't apply codecs filters correctly

Add overlap detection in resolve_end_times. When consecutive tracks have
overlapping time ranges (end of track N > start of track N+1), a warning
is printed but processing continues as before.

audio_splitter/constants.py

@@ -1,20 +1,124 @@
-"""Global constants and default values."""
+# audio_splitter/constants.py
+"""Global constants for the audio splitter.
 
-# Mapping from user‑friendly format names to FFmpeg format identifiers,
+This file serves as the single source of truth for:
-# file extensions, and whether the container is audio‑only.
+- Container formats and their properties
-FORMAT_INFO = {
+- Audio codecs and their recommended containers
-    'mp3':      {'ffmpeg': 'mp3',      'ext': '.mp3',  'audio_only': True},
+- Video codec support per container
-    'm4a':      {'ffmpeg': 'mp4',      'ext': '.m4a',  'audio_only': True},
+- File extensions for each codec/container combination
-    'mp4':      {'ffmpeg': 'mp4',      'ext': '.mp4',  'audio_only': False},
+- Compatibility matrix for codec/container validation
-    'mkv':      {'ffmpeg': 'matroska', 'ext': '.mkv',  'audio_only': False},
+
-    'matroska': {'ffmpeg': 'matroska', 'ext': '.mkv',  'audio_only': False},
+Codec != Container != File Extension.
-    'ogg':      {'ffmpeg': 'ogg',      'ext': '.ogg',  'audio_only': True},
+Example: Opus (codec) → Ogg (container) → .opus (extension)
-    'opus':     {'ffmpeg': 'ogg',      'ext': '.opus', 'audio_only': True},
+"""
-    'flac':     {'ffmpeg': 'flac',     'ext': '.flac', 'audio_only': True},
+from typing import Dict, Optional
-    'wav':      {'ffmpeg': 'wav',      'ext': '.wav',  'audio_only': True},
+
-    'aac':      {'ffmpeg': 'adts',     'ext': '.aac',  'audio_only': True},
+# ------------------------------------------------------------------------------
+# Container information
+# ------------------------------------------------------------------------------
+CONTAINER_INFO = [
+    # Audio-only containers
+    {'name': 'mp3', 'ffmpeg': 'mp3', 'extension': '.mp3', 'supports_video': True, 'supports_subs': False},
+    {'name': 'm4a', 'ffmpeg': 'mp4', 'extension': '.m4a', 'supports_video': False, 'supports_subs': False},
+    {'name': 'flac', 'ffmpeg': 'flac', 'extension': '.flac', 'supports_video': False, 'supports_subs': False},
+    {'name': 'wav', 'ffmpeg': 'wav', 'extension': '.wav', 'supports_video': False, 'supports_subs': False},
+    {'name': 'aac', 'ffmpeg': 'adts', 'extension': '.aac', 'supports_video': False, 'supports_subs': False},
+    # Containers that support video and subtitles
+    {'name': 'mp4', 'ffmpeg': 'mp4', 'extension': '.mp4', 'supports_video': True, 'supports_subs': True},
+    {'name': 'mkv', 'ffmpeg': 'matroska', 'extension': '.mkv', 'supports_video': True, 'supports_subs': True},
+    {'name': 'ogg', 'ffmpeg': 'ogg', 'extension': '.ogg', 'supports_video': True, 'supports_subs': True},
+    {'name': 'webm', 'ffmpeg': 'webm', 'extension': '.webm', 'supports_video': True, 'supports_subs': False},
+]
+
+# Container name lookup set for fast membership checks
+CONTAINER_NAMES = {container['name'] for container in CONTAINER_INFO}
+
+
+def get_container_info(container_name: str) -> Optional[Dict]:
+    """Return container info dict or None if not found."""
+    for container in CONTAINER_INFO:
+        if container['name'] == container_name:
+            return container
+    return None
+
+
+# ------------------------------------------------------------------------------
+# Codec information
+# ------------------------------------------------------------------------------
+CODEC_INFO = [
+    # Audio codecs
+    {'name': 'opus', 'ffmpeg': 'libopus', 'recommended_container': 'ogg', 'recommended_extension': '.opus', 'codec_type': 'audio'},
+    {'name': 'vorbis', 'ffmpeg': 'libvorbis', 'recommended_container': 'ogg', 'recommended_extension': '.ogg', 'codec_type': 'audio'},
+    {'name': 'flac', 'ffmpeg': 'flac', 'recommended_container': 'flac', 'recommended_extension': '.flac', 'codec_type': 'audio'},
+    {'name': 'aac', 'ffmpeg': 'aac', 'recommended_container': 'mp4', 'recommended_extension': '.m4a', 'codec_type': 'audio'},
+    {'name': 'mp3', 'ffmpeg': 'libmp3lame', 'recommended_container': 'mp3', 'recommended_extension': '.mp3', 'codec_type': 'audio'},
+    {'name': 'alac', 'ffmpeg': 'alac', 'recommended_container': 'mp4', 'recommended_extension': '.m4a', 'codec_type': 'audio'},
+    {'name': 'pcm_s16le', 'ffmpeg': 'pcm_s16le', 'recommended_container': 'wav', 'recommended_extension': '.wav', 'codec_type': 'audio'},
+    # Video codecs (including cover images)
+    {'name': 'theora', 'ffmpeg': 'libtheora', 'recommended_container': 'ogg', 'recommended_extension': '.ogv', 'codec_type': 'video'},
+    {'name': 'vp8', 'ffmpeg': 'libvpx', 'recommended_container': 'webm', 'recommended_extension': '.webm', 'codec_type': 'video'},
+    {'name': 'vp9', 'ffmpeg': 'libvpx-vp9', 'recommended_container': 'webm', 'recommended_extension': '.webm', 'codec_type': 'video'},
+    {'name': 'av1', 'ffmpeg': 'libaom-av1', 'recommended_container': 'mkv', 'recommended_extension': '.mkv', 'codec_type': 'video'},
+    {'name': 'h264', 'ffmpeg': 'libx264', 'recommended_container': 'mp4', 'recommended_extension': '.mp4', 'codec_type': 'video'},
+    {'name': 'h265', 'ffmpeg': 'libx265', 'recommended_container': 'mp4', 'recommended_extension': '.mp4', 'codec_type': 'video'},
+    {'name': 'png', 'ffmpeg': 'png', 'recommended_container': 'ogg', 'recommended_extension': '.png', 'codec_type': 'video'},
+    {'name': 'mjpeg', 'ffmpeg': 'mjpeg', 'recommended_container': 'ogg', 'recommended_extension': '.jpg', 'codec_type': 'video'},
+    # Subtitle codecs
+    {'name': 'srt', 'ffmpeg': 'srt', 'recommended_container': 'mkv', 'recommended_extension': '.srt', 'codec_type': 'subtitle'},
+    {'name': 'ass', 'ffmpeg': 'ass', 'recommended_container': 'mkv', 'recommended_extension': '.ass', 'codec_type': 'subtitle'},
+    {'name': 'vtt', 'ffmpeg': 'webvtt', 'recommended_container': 'webm', 'recommended_extension': '.vtt', 'codec_type': 'subtitle'},
+]
+
+# Map codec name → recommended container
+CODEC_TO_CONTAINER_MAP = {codec['name']: codec['recommended_container'] for codec in CODEC_INFO}
+CODEC_TO_EXTENSION_MAP = {codec['name']: codec['recommended_extension'] for codec in CODEC_INFO}
+
+# Map codec name → FFmpeg encoder name
+CODEC_NAME_TO_FFMPEG = {codec['name']: codec['ffmpeg'] for codec in CODEC_INFO}
+
+# ------------------------------------------------------------------------------
+# Compatibility matrix: container → supported audio and video codecs
+# ------------------------------------------------------------------------------
+# Each container entry maps to a dict with 'audio' and 'video' keys.
+# - 'audio': list of audio codec names that are supported in this container.
+#            Use None to indicate that any audio codec is supported.
+# - 'video': list of video codec names that are supported in this container.
+#            Use None to indicate that any video codec is supported.
+#            Empty list means no video support (audio-only container).
+COMPATIBILITY_MATRIX = {
+    'mp3': {'audio': ['mp3'], 'video': ['png', 'mjpeg']},
+    'm4a': {'audio': ['aac', 'alac', 'opus', 'flac'], 'video': []},
+    'mp4': {'audio': ['aac', 'alac', 'opus', 'flac', 'mp3'], 'video': ['h264', 'h265', 'vp9', 'av1']},
+    'mkv': {'audio': None, 'video': None},
+    'ogg': {'audio': ['opus', 'vorbis', 'flac'], 'video': ['theora', 'vp8', 'png', 'mjpeg']},
+    'webm': {'audio': ['opus', 'vorbis'], 'video': ['vp8', 'vp9', 'av1']},
+    'flac': {'audio': ['flac'], 'video': ['png', 'mjpeg']},
+    'wav': {'audio': ['pcm_s16le'], 'video': []},
+    'aac': {'audio': ['aac'], 'video': []},
 }
 
-# Default characters to replace when --replace-bad-chars is enabled.
+# ------------------------------------------------------------------------------
-# Includes common punctuation, single quote, and a trailing space.
+# Helper functions for compatibility checking
-DEFAULT_BAD_CHARS = r',!@#№$;:%^&?*(){}[]\/<>+=~`\' '
+# ------------------------------------------------------------------------------
+def is_audio_codec_supported(container: str, audio_codec: str) -> bool:
+    """Check if an audio codec is supported in the given container."""
+    entry = COMPATIBILITY_MATRIX.get(container, {})
+    supported = entry.get('audio')
+    if supported is None:
+        return True
+    return audio_codec in supported
+
+
+def is_video_codec_supported(container: str, video_codec: str) -> bool:
+    """Check if a video codec is supported in the given container."""
+    entry = COMPATIBILITY_MATRIX.get(container, {})
+    supported = entry.get('video')
+    if supported is None:
+        return True
+    return video_codec in supported
+
+
+# ------------------------------------------------------------------------------
+# Default bad characters (for filename sanitization)
+# ------------------------------------------------------------------------------
+DEFAULT_BAD_CHARS = r'!@#№$;:%^&?*(){}[]\/<>+=~`\'|," '

audio_splitter/core.py

@@ -1,36 +1,87 @@
-"""Core logic: orchestrates the splitting process."""
+# audio_splitter/core.py
+"""Core splitting logic – orchestrates the entire split process."""
 
 import os
 import subprocess
+import sys
+from typing import List, Dict, Any
 
-from .constants import FORMAT_INFO
+from .constants import (
-from .ffmpeg import get_audio_duration, get_stream_info, get_metadata, build_ffmpeg_command
+    CONTAINER_INFO,
-from .formats import determine_output_format, validate_format_compatibility
+    CONTAINER_NAMES,
+    CODEC_TO_EXTENSION_MAP,
+    CODEC_NAME_TO_FFMPEG,
+)
+from .ffmpeg import (
+    get_audio_duration,
+    get_stream_info,
+    get_metadata,
+    build_ffmpeg_command,
+    is_attached_picture,
+    extract_cover_image,
+)
+from .formats import (
+    determine_output_format,
+    validate_format_compatibility,
+)
+from .handlers import get_handler, needs_drop_video
 from .timestamp import parse_track_timestamps, resolve_end_times
 from .filename import build_filename
 from .metadata import build_metadata_dict
 from .utils import format_time
 
 
-def split_audio(input_file, output_directory, tracks, args):
+def split_audio(input_file: str, output_directory: str, tracks: List[Dict[str, Any]], args) -> None:
     """
     Main orchestration function: split the audio file into tracks.
 
     Args:
         input_file: Path to the input media file.
         output_directory: Directory where output files will be saved.
-        tracks: List of dicts, each containing parsed fields.
+        tracks: List of dicts, each containing parsed fields (ts, tn, an, ...).
-        args: Parsed command‑line arguments (namespace).
+        args: Parsed command‑line arguments (namespace) with attributes:
+            - container: output container name (or None for auto-detect)
+            - audio_codec: audio codec (copy or encoder)
+            - video_codec: video codec (copy or encoder)
+            - subtitle_codec: subtitle codec (copy or encoder)
+            - video_quality: integer or None
+            - drop_video: bool
+            - drop_subs: bool
+            - number_tracks: bool
+            - output_template: str
+            - replace_bad_chars: bool
+            - replacement_char: str
+            - bad_chars: str
+            - skip_existing: bool
+            - album: str or None
+            - comment: str or None
+            - no_comment: bool
+            - comment_stream: int or None
+            - merge_comments: bool
+            - comment_separator: str
+            - delete_original: bool
+            - cover_image: List[str] or None (optional, CLI list of cover image paths)
 
     Raises:
         RuntimeError: If no audio stream is found.
-        ValueError: If timestamp parsing or format compatibility fails.
+        ValueError: If compatibility validation fails.
     """
     # --------------------------------------------------------------------------
     # 1. Setup
     # --------------------------------------------------------------------------
     os.makedirs(output_directory, exist_ok=True)
 
+    # Check write permission on output directory.
+    try:
+        test_file = os.path.join(output_directory, f'.write_test_{os.getpid()}')
+        with open(test_file, 'w') as f:
+            f.write('test')
+        os.remove(test_file)
+    except PermissionError:
+        raise RuntimeError(
+            f"Error: No write permission for output directory: {output_directory}"
+        )
+
     total_duration = get_audio_duration(input_file)
     stream_info = get_stream_info(input_file)
 
@@ -42,26 +93,62 @@ def split_audio(input_file, output_directory, tracks, args):
         raise RuntimeError("No audio stream found in input file.")
 
     # --------------------------------------------------------------------------
-    # 2. Format decision
+    # 2. Determine output container
     # --------------------------------------------------------------------------
-    output_format = determine_output_format(stream_info, args.format, args.transcode_to, input_file=input_file)
+    user_container = getattr(args, 'container', None)
-    print(f"Output container: {output_format}")
+    output_container = determine_output_format(
-
+        stream_info,
-    validate_format_compatibility(output_format, stream_info,
+        user_format=user_container,
-                                  args.drop_video, args.drop_subs)
+        transcode_audio=args.audio_codec if args.audio_codec != 'copy' else None,
-
+        input_file=input_file
-    # Determine file extension.
+    )
-    extension_info = FORMAT_INFO.get(output_format, {})
+    print(f"Output container: {output_container}")
-    extension = extension_info.get('ext', '.mkv')
 
     # --------------------------------------------------------------------------
-    # 3. Parse timestamps
+    # 3. Validate compatibility
+    # --------------------------------------------------------------------------
+    try:
+        validate_format_compatibility(
+            container=output_container,
+            stream_info=stream_info,
+            drop_video=args.drop_video,
+            drop_subs=args.drop_subs,
+            input_file=input_file,
+            audio_codec=args.audio_codec,
+            video_codec=args.video_codec,
+        )
+    except ValueError as e:
+        raise RuntimeError(f"Compatibility error: {e}")
+
+    # --------------------------------------------------------------------------
+    # 4. Determine output audio codec and extension
+    # --------------------------------------------------------------------------
+    # Determine the audio codec that will be used in the output
+    if args.audio_codec != 'copy':
+        output_audio_codec = args.audio_codec
+    else:
+        output_audio_codec = stream_info.get('audio_codec', '')
+
+    # Choose extension based on the output container, not the audio codec.
+    # When user specifies --container, the file extension must match the container.
+    container_info = next((c for c in CONTAINER_INFO if c['name'] == output_container), None)
+    if container_info:
+        extension = container_info['extension']
+    elif output_audio_codec in CODEC_TO_EXTENSION_MAP:
+        extension = CODEC_TO_EXTENSION_MAP[output_audio_codec]
+    else:
+        extension = '.mkv'
+
+    print(f"Output extension: {extension}")
+
+    # --------------------------------------------------------------------------
+    # 5. Parse timestamps
     # --------------------------------------------------------------------------
     track_times = parse_track_timestamps(tracks)
     resolved_times = resolve_end_times(track_times, total_duration)
 
     # --------------------------------------------------------------------------
-    # 4. Fetch original metadata (for fallbacks)
+    # 6. Fetch original metadata (for fallbacks)
     # --------------------------------------------------------------------------
     input_metadata = get_metadata(input_file)
     original_album = input_metadata.get('album')
@@ -78,7 +165,39 @@ def split_audio(input_file, output_directory, tracks, args):
             print(f"  Stream {idx}: '{comment}'")
 
     # --------------------------------------------------------------------------
-    # 5. Process each track
+    # 7. Handle attached picture (cover art)
+    # --------------------------------------------------------------------------
+    user_cover_images = getattr(args, 'cover_image', None)
+    # Resolve per-track cover images: single image reused, or one-per-track
+    track_cover_images = []
+    if user_cover_images:
+        for img in user_cover_images:
+            if os.path.exists(img):
+                track_cover_images.append(img)
+            else:
+                print(f"Warning: Cover image not found, skipping: {img}")
+    # Extract cover from input if no user cover and input has video
+    if not track_cover_images and not args.drop_video and stream_info.get('has_video'):
+        if is_attached_picture(input_file):
+            cover_image_path = os.path.join(output_directory, 'cover.png')
+            if extract_cover_image(input_file, cover_image_path):
+                track_cover_images.append(cover_image_path)
+                print("Extracted cover image for all tracks.")
+            else:
+                track_cover_images = []
+
+    # Check if we need special handling (e.g., Opus files need opustags)
+    # Use output_audio_codec (not input_audio_codec) so the handler is resolved
+    # against the actual output codec (e.g., transcoding aac→opus in ogg).
+    input_audio_codec = stream_info.get('audio_codec')
+    cover_handler = get_handler(output_container, output_audio_codec)
+    needs_drop = needs_drop_video(output_container, output_audio_codec)
+    if track_cover_images and needs_drop:
+        print(f"Using special handler for {output_container} + {output_audio_codec}")
+        print("Temporarily dropping video for opustags post-processing.")
+
+    # --------------------------------------------------------------------------
+    # 8. Process each track
     # --------------------------------------------------------------------------
     for idx, track in enumerate(tracks, start=1):
         start_seconds, end_seconds = resolved_times[idx - 1]
@@ -91,31 +210,62 @@ def split_audio(input_file, output_directory, tracks, args):
         track_name = track.get('tn', 'Unknown')
 
         # ----------------------------------------------------------------------
-        # 5a. Build filename
+        # 8a. Build filename
         # ----------------------------------------------------------------------
         clean_filename = build_filename(track, idx, extension, args)
         output_path = os.path.join(output_directory, clean_filename)
 
         # ----------------------------------------------------------------------
-        # 5b. Handle existing files
+        # 8b. Handle existing files
         # ----------------------------------------------------------------------
         if args.skip_existing and os.path.exists(output_path):
             print(f"Skipping track {idx}: {output_path} already exists.")
             continue
 
         # ----------------------------------------------------------------------
-        # 5c. Build metadata
+        # 8c. Build metadata
         # ----------------------------------------------------------------------
         metadata = build_metadata_dict(track, idx, input_metadata, args)
 
         # ----------------------------------------------------------------------
-        # 5d. Build and execute FFmpeg command
+        # 8d. Build and execute FFmpeg command
         # ----------------------------------------------------------------------
+        # Map codec names to FFmpeg encoder names
+        audio_enc = args.audio_codec
+        if audio_enc != 'copy':
+            audio_enc = CODEC_NAME_TO_FFMPEG.get(audio_enc, audio_enc)  # fallback to itself if not found
+        video_enc = args.video_codec
+        if video_enc != 'copy':
+            video_enc = CODEC_NAME_TO_FFMPEG.get(video_enc, video_enc)
+        subtitle_enc = args.subtitle_codec
+        if subtitle_enc != 'copy':
+            subtitle_enc = CODEC_NAME_TO_FFMPEG.get(subtitle_enc, subtitle_enc)
+        
+        # Then build command with these mapped encoders
+        # Use temporary drop_video for handlers that need it
+        effective_drop_video = args.drop_video or (track_cover_images and needs_drop)
+        # For handlers that need opustags post-processing, don't pass cover_image_path
+        # to ffmpeg - it will process audio-only, then handler adds cover afterward
+        per_track_cover = (
+            track_cover_images[idx - 1] if len(track_cover_images) == len(tracks)
+            else (track_cover_images[0] if track_cover_images else None)
+        )
+        ffmpeg_cover_path = None if (per_track_cover and needs_drop) else per_track_cover
         cmd = build_ffmpeg_command(
-            input_file, start_seconds, duration_seconds, output_path,
+            input_file=input_file,
-            stream_info, output_format, args.transcode_to,
+            start_seconds=start_seconds,
-            args.drop_video, args.drop_subs,
+            duration_seconds=duration_seconds,
-            metadata=metadata
+            output_path=output_path,
+            stream_info=stream_info,
+            format_opt=output_container,
+            audio_codec=audio_enc,
+            video_codec=video_enc,
+            subtitle_codec=subtitle_enc,
+            metadata=metadata,
+            cover_image_path=ffmpeg_cover_path,
+            video_quality=getattr(args, 'video_quality', None),
+            drop_video=effective_drop_video,
+            drop_subs=args.drop_subs,
         )
 
         print(f"Extracting track {idx}: {track_name} "
@@ -128,3 +278,28 @@ def split_audio(input_file, output_directory, tracks, args):
             print(result.stderr)
         else:
             print(f"  -> Saved to: {output_path}")
+            # Apply cover image handler if needed
+            if per_track_cover and needs_drop:
+                print(f"Applying cover image via {output_container} handler...")
+                if not cover_handler(
+                    input_file=input_file,
+                    cover_image_path=per_track_cover,
+                    output_path=output_path,
+                    stream_info=stream_info,
+                    audio_codec=audio_enc,
+                    video_codec=video_enc,
+                    video_quality=getattr(args, 'video_quality', None),
+                    drop_video=args.drop_video,
+                    drop_subs=args.drop_subs,
+                ):
+                    print(f"Warning: Failed to attach cover image to {output_path}")
+
+    # --------------------------------------------------------------------------
+    # 9. Delete original file if requested
+    # --------------------------------------------------------------------------
+    if getattr(args, 'delete_original', False):
+        try:
+            os.remove(input_file)
+            print(f"Deleted original file: {input_file}")
+        except OSError as e:
+            print(f"Warning: Could not delete original file: {e}")

audio_splitter/ffmpeg.py

@@ -1,10 +1,12 @@
-"""FFmpeg/FFprobe interaction utilities for the CLI and web backend."""
+# audio_splitter/ffmpeg.py
+"""FFmpeg/FFprobe interaction utilities."""
 
 import json
+import os
 import subprocess
 from typing import Dict, List, Optional, Tuple
 
-from .constants import FORMAT_INFO
+from .constants import CONTAINER_INFO
 from .utils import format_time
 
 
@@ -75,6 +77,28 @@ def get_audio_codec(input_file: str) -> Optional[str]:
     return codec if codec else None
 
 
+def get_video_codec(input_file: str) -> Optional[str]:
+    """
+    Return the codec name of the first video stream.
+
+    Args:
+        input_file: Path to the media file.
+
+    Returns:
+        Codec name as a lowercase string, or None if no video stream exists.
+    """
+    cmd = [
+        'ffprobe', '-v', 'error',
+        '-select_streams', 'v:0',
+        '-show_entries', 'stream=codec_name',
+        '-of', 'default=noprint_wrappers=1:nokey=1',
+        input_file
+    ]
+    result = subprocess.run(cmd, capture_output=True, text=True, check=False)
+    codec = result.stdout.strip().lower()
+    return codec if codec else None
+
+
 def get_stream_info(input_file: str) -> Dict[str, any]:
     """
     Collect information about the streams present in the input file.
@@ -136,7 +160,7 @@ def get_metadata(input_file: str) -> Dict[str, any]:
 
 def get_container_format(input_file: str) -> Optional[str]:
     """
-    Retrieve the container format name (e.g., 'mp4', 'mp3', 'matroska') from the input file.
+    Retrieve the container format name (e.g., 'mp4', 'mp3', 'mkv') from the input file.
 
     Args:
         input_file: Path to the media file.
@@ -156,69 +180,237 @@ def get_container_format(input_file: str) -> Optional[str]:
     format_name = result.stdout.strip().split(',')[0]  # take first if multiple
     if not format_name:
         return None
-    # Normalize common aliases to names used in FORMAT_INFO (container only, not codec-specific)
+    # Normalize common aliases to names used in CONTAINER_INFO
-    # This mapping is purely for container identification.
     mapping = {
-        'mpeg': 'mp3',       # MPEG-1/2 audio (MP3) container
+        'mpeg': 'mp3',
         'mp2': 'mp3',
         'mp4': 'mp4',
-        'm4a': 'mp4',        # M4A is MP4 container
+        'm4a': 'mp4',
-        'mov': 'mp4',        # QuickTime is MP4-like
+        'mov': 'mp4',
         '3gp': 'mp4',
-        'matroska': 'matroska',
+        'matroska': 'mkv',
-        'webm': 'matroska',  # WebM uses Matroska container
+        'webm': 'mkv',
         'ogg': 'ogg',
         'flac': 'flac',
         'wav': 'wav',
         'aac': 'aac',
         'opus': 'opus',
         'mp3': 'mp3',
-        'adts': 'aac',       # raw AAC in ADTS container
+        'adts': 'aac',
-        'amr': 'amr',        # AMR container (rare)
+        'amr': 'amr',
     }
     return mapping.get(format_name, format_name)
 
 
-def build_ffmpeg_command(input_file: str, start_seconds: int, duration_seconds: int,
+MAX_COVER_IMAGE_SIZE_MB = 4
-                         output_path: str, stream_info: Dict, format_opt: Optional[str],
-                         transcode_audio: Optional[str], drop_video: bool, drop_subs: bool,
-                         metadata: Optional[Dict] = None) -> List[str]:
-    """
-    Construct the FFmpeg command line as a list of arguments.
 
-    Args:
+
-        input_file: Path to the input media file.
+def has_cover_or_video(input_file: str) -> bool:
-        start_seconds: Start time for the segment (in seconds).
+    """
-        duration_seconds: Duration of the segment (in seconds).
+    Check if the input file contains a cover image (attached picture) or any video track.
-        output_path: Destination path for the output file.
-        stream_info: Dictionary from get_stream_info().
-        format_opt: Output container format (e.g., 'mp3').
-        transcode_audio: Audio codec to transcode to (or None).
-        drop_video: True to remove video streams.
-        drop_subs: True to remove subtitle streams.
-        metadata: Optional dict of metadata key/value pairs to write.
 
     Returns:
-        A list of command‑line arguments suitable for subprocess.run().
+        True if a cover image or video stream is detected, False otherwise.
     """
     cmd = [
-        'ffmpeg',
+        'ffprobe', '-v', 'quiet',
-        '-i', input_file,
+        '-print_format', 'json',
-        '-ss', format_time(start_seconds),
+        '-select_streams', 'v',
-        '-t', format_time(duration_seconds)
+        '-show_entries', 'stream=codec_type,codec_name,disposition',
+        input_file
     ]
+    result = subprocess.run(cmd, capture_output=True, text=True, check=False)
+    if result.returncode != 0:
+        return False
 
-    # Clear all original metadata.
+    try:
+        data = json.loads(result.stdout)
+        streams = data.get('streams', [])
+        return len(streams) > 0
+    except (json.JSONDecodeError, KeyError):
+        return False
+
+
+def validate_cover_images(cover_images: List[str], num_tracks: int) -> None:
+    """
+    Validate cover image(s) before splitting.
+
+    Checks:
+        - Each file exists
+        - Only PNG and JPEG formats are accepted
+        - Single image OR count matches number of tracks
+        - File size warning for images > 4 MB
+
+    Args:
+        cover_images: List of cover image paths (single image or multiple).
+        num_tracks: Number of tracks in the tracklist.
+
+    Raises:
+        ValueError: If validation fails.
+    """
+    if len(cover_images) == 0:
+        return
+
+    if len(cover_images) == 1 and num_tracks > 1:
+        # Single image is fine - will be reused for all tracks
+        pass
+    elif len(cover_images) == num_tracks:
+        pass
+    else:
+        raise ValueError(
+            f"Cover image count ({len(cover_images)}) must be 1 or match "
+            f"the number of tracks ({num_tracks})."
+        )
+
+    for img_path in cover_images:
+        if not os.path.exists(img_path):
+            raise ValueError(f"Cover image not found: {img_path}")
+
+        ext = os.path.splitext(img_path)[1].lower()
+        if ext not in ('.png', '.jpg', '.jpeg'):
+            raise ValueError(
+                f"Unsupported cover image format '{ext}' for '{img_path}'. "
+                f"Only PNG and JPEG are supported."
+            )
+
+        size_mb = os.path.getsize(img_path) / (1024 * 1024)
+        if size_mb > MAX_COVER_IMAGE_SIZE_MB:
+            print(
+                f"Warning: Cover image '{img_path}' is {size_mb:.1f} MB "
+                f"(exceeds {MAX_COVER_IMAGE_SIZE_MB} MB limit). "
+                f"Large images may cause issues."
+            )
+
+
+def is_attached_picture(input_file: str) -> bool:
+    """
+    Check if the input file has a video stream that is an attached picture (cover art).
+
+    Detection logic:
+        1. If there is a video stream with disposition.attached_pic == 1, return True.
+        2. Otherwise, if there is exactly one video stream and its codec is an image
+           format (PNG, MJPEG, JPEG, GIF, BMP), return True.
+
+    Returns:
+        True if a cover image is detected, False otherwise.
+    """
+    cmd = [
+        'ffprobe', '-v', 'quiet',
+        '-print_format', 'json',
+        '-select_streams', 'v',
+        '-show_entries', 'stream=codec_name,disposition',
+        input_file
+    ]
+    result = subprocess.run(cmd, capture_output=True, text=True, check=False)
+    if result.returncode != 0:
+        return False
+
+    try:
+        data = json.loads(result.stdout)
+        streams = data.get('streams', [])
+        if not streams:
+            return False
+
+        # Check each stream
+        for stream in streams:
+            codec = stream.get('codec_name', '').lower()
+            disposition = stream.get('disposition', {})
+            # If attached_pic is set, it's a cover image
+            if disposition.get('attached_pic') == 1:
+                return True
+            # If not, check if it's an image codec and we have exactly one video stream
+            if codec in ('png', 'mjpeg', 'jpeg', 'gif', 'bmp'):
+                # If there is exactly one video stream, treat it as cover
+                if len(streams) == 1:
+                    return True
+        return False
+    except (json.JSONDecodeError, KeyError):
+        return False
+
+
+def extract_cover_image(input_file: str, output_path: str) -> bool:
+    """
+    Extract the first frame of the video stream (assumed to be an attached picture)
+    and save it to output_path.
+
+    Returns:
+        True if extraction succeeded, False otherwise.
+    """
+    cmd = [
+        'ffmpeg', '-i', input_file,
+        '-map', '0:v:0',
+        '-frames:v', '1',
+        '-y',
+        output_path
+    ]
+    result = subprocess.run(cmd, capture_output=True, text=True, check=False)
+    if result.returncode != 0:
+        print(f"Failed to extract cover image: {result.stderr}")
+        return False
+    return True
+
+
+def _build_inputs(cmd: List[str], input_file: str, cover_image_path: Optional[str]) -> None:
+    """Add input files to the command."""
+    if cover_image_path:
+        cmd.extend(['-i', cover_image_path])
+    cmd.extend(['-i', input_file])
+
+
+def _build_time_options(cmd: List[str], start_seconds: int, duration_seconds: int) -> None:
+    """Add time-based options to the command."""
+    cmd.extend(['-ss', format_time(start_seconds), '-t', format_time(duration_seconds)])
+
+
+def _build_metadata(cmd: List[str], metadata: Optional[Dict]) -> None:
+    """Add metadata options to the command."""
     cmd.append('-map_metadata')
     cmd.append('-1')
-
-    # Apply custom metadata.
     if metadata:
         for key, value in metadata.items():
             if value is not None and value != '':
                 cmd.extend(['-metadata', f"{key}={value}"])
 
-    # Stream mapping.
+
+def _build_cover_image_mapping(
+    cmd: List[str],
+    audio_codec: Optional[str],
+    video_codec: Optional[str],
+    video_quality: Optional[int],
+) -> None:
+    """Build stream mapping for cover image extraction (audio + cover video)."""
+    cmd.extend(['-map', '1:a:0', '-map', '0:v:0'])
+
+    if video_codec and video_codec != 'copy':
+        cmd.extend(['-c:v', video_codec])
+    else:
+        cmd.extend(['-c:v', 'png'])
+
+    if audio_codec and audio_codec != 'copy':
+        cmd.extend(['-c:a', audio_codec])
+    else:
+        cmd.extend(['-c:a', 'copy'])
+
+    # Preserve attached_pic disposition for cover image
+    cmd.extend(['-disposition', 'attached_pic'])
+
+    cmd.append('-sn')
+
+    if video_quality is not None:
+        cmd.extend(['-q:v', str(video_quality)])
+
+
+def _build_standard_mapping(
+    cmd: List[str],
+    stream_info: Dict,
+    audio_codec: Optional[str],
+    video_codec: Optional[str],
+    subtitle_codec: Optional[str],
+    video_quality: Optional[int],
+    drop_video: bool,
+    drop_subs: bool,
+) -> None:
+    """Build stream mapping for standard extraction (no cover image)."""
     if drop_video and drop_subs:
         cmd.extend(['-map', '0:a:0'])
     elif drop_video:
@@ -228,32 +420,97 @@ def build_ffmpeg_command(input_file: str, start_seconds: int, duration_seconds:
     else:
         cmd.extend(['-map', '0'])
 
-    # Audio codec.
+    if audio_codec and audio_codec != 'copy':
-    if transcode_audio:
+        cmd.extend(['-c:a', audio_codec])
-        cmd.extend(['-c:a', transcode_audio])
-        if transcode_audio in ('libmp3lame', 'mp3'):
-            cmd.extend(['-b:a', '192k'])
-        elif transcode_audio in ('libopus', 'opus'):
-            cmd.extend(['-b:a', '128k'])
     else:
         cmd.extend(['-c:a', 'copy'])
 
-    # Video codec.
+    if not drop_video and stream_info.get('has_video'):
-    if not drop_video and stream_info['has_video']:
+        if video_codec and video_codec != 'copy':
+            cmd.extend(['-c:v', video_codec])
+            if video_quality is not None:
+                cmd.extend(['-q:v', str(video_quality)])
+        else:
             cmd.extend(['-c:v', 'copy'])
     else:
         cmd.append('-vn')
 
-    # Subtitle codec.
+    if not drop_subs and stream_info.get('has_subtitle'):
-    if not drop_subs and stream_info['has_subtitle']:
+        if subtitle_codec and subtitle_codec != 'copy':
+            cmd.extend(['-c:s', subtitle_codec])
+        else:
             cmd.extend(['-c:s', 'copy'])
     else:
         cmd.append('-sn')
 
-    # Output format.
+
+def _build_format(cmd: List[str], format_opt: Optional[str]) -> None:
+    """Add output format option if specified."""
     if format_opt:
-        ffmpeg_format = FORMAT_INFO.get(format_opt, {}).get('ffmpeg', format_opt)
+        ffmpeg_format = next((c['ffmpeg'] for c in CONTAINER_INFO if c['name'] == format_opt), format_opt)
         cmd.extend(['-f', ffmpeg_format])
 
+
+def _build_output(cmd: List[str], output_path: str) -> None:
+    """Add output file to the command."""
     cmd.extend(['-y', output_path])
+
+
+def build_ffmpeg_command(
+    input_file: str,
+    start_seconds: int,
+    duration_seconds: int,
+    output_path: str,
+    stream_info: Dict,
+    format_opt: Optional[str],
+    audio_codec: Optional[str] = 'copy',
+    video_codec: Optional[str] = 'copy',
+    subtitle_codec: Optional[str] = 'copy',
+    metadata: Optional[Dict] = None,
+    cover_image_path: Optional[str] = None,
+    video_quality: Optional[int] = None,
+    drop_video: bool = False,
+    drop_subs: bool = False,
+) -> List[str]:
+    """
+    Construct the FFmpeg command line as a list of arguments.
+
+    Args:
+        input_file: Path to the input media file.
+        start_seconds: Start time for the segment (in seconds).
+        duration_seconds: Duration of the segment (in seconds).
+        output_path: Destination path for the output file.
+        stream_info: Dictionary from get_stream_info().
+        format_opt: Output container format (e.g., 'mp3', 'mkv').
+        audio_codec: Audio codec to use ('copy' or encoder name like 'libopus').
+        video_codec: Video codec to use ('copy' or encoder name).
+        subtitle_codec: Subtitle codec to use ('copy' or encoder name).
+        metadata: Optional dict of metadata key/value pairs to write.
+        cover_image_path: Path to extracted cover image (if any).
+        video_quality: Quality value for video encoder (e.g., 1-31, lower=better).
+        drop_video: If True, remove video streams.
+        drop_subs: If True, remove subtitle streams.
+
+    Returns:
+        A list of command‑line arguments suitable for subprocess.run().
+    """
+    cmd = ['ffmpeg']
+
+    _build_inputs(cmd, input_file, cover_image_path)
+    _build_time_options(cmd, start_seconds, duration_seconds)
+    _build_metadata(cmd, metadata)
+
+    if cover_image_path:
+        _build_cover_image_mapping(cmd, audio_codec, video_codec, video_quality)
+    else:
+        _build_standard_mapping(
+            cmd, stream_info, audio_codec, video_codec, subtitle_codec,
+            video_quality, drop_video, drop_subs
+        )
+
+    _build_format(cmd, format_opt)
+    _build_output(cmd, output_path)
+
     return cmd
+
+

audio_splitter/filename.py

@@ -41,7 +41,18 @@ def build_filename(track, idx, extension, args):
         clean_filename = apply_replacement(raw_filename,
                                            args.bad_chars,
                                            args.replacement_char)
-        clean_filename = cleanup_good_chars(clean_filename, args.replacement_char)
+        # Split off the file extension before cleanup so trailing
+        # replacement chars don't leak into the name portion.
+        name_part, _, ext_part = clean_filename.rpartition('.')
+        clean_filename = cleanup_good_chars(name_part, args.replacement_char)
+        # Strip leading/trailing separator characters (replacement char,
+        # hyphen, etc.) that may result from empty fields or bad-char
+        # sequences adjacent to template separators.
+        clean_filename = clean_filename.strip(f'{args.replacement_char}-')
+        # Fallback: if cleanup leaves an empty name, use the track number.
+        if not clean_filename:
+            clean_filename = f"{idx:02d}"
+        clean_filename = f"{clean_filename}.{ext_part}"
     else:
         clean_filename = raw_filename
         # Warn about unsafe characters.

audio_splitter/formats.py

@@ -1,19 +1,28 @@
+# audio_splitter/formats.py
 """Container format decision and validation."""
 
 from typing import Dict, Optional
 
-from .constants import FORMAT_INFO
+from .constants import (
+    CONTAINER_NAMES,
+    CONTAINER_INFO,
+    CODEC_TO_CONTAINER_MAP,
+    COMPATIBILITY_MATRIX,
+    is_audio_codec_supported,
+    is_video_codec_supported,
+)
+from .defaults import DEFAULT_FORMAT
 
 
 def determine_default_format(container: Optional[str], codec: Optional[str]) -> Optional[str]:
     """
     Given the container format and audio codec, determine the recommended output format.
 
-    This is used when the user has not explicitly specified a format.
+    Uses the CODEC_TO_CONTAINER_MAP to map codec → container.
-    It prioritizes the codec to choose the most appropriate container/extension.
+    If the codec is not found, it falls back to the container.
 
     Args:
-        container: Container name (e.g., 'ogg', 'mp4', 'matroska') as returned by get_container_format().
+        container: Container name (e.g., 'ogg', 'mp4', 'mkv') as returned by get_container_format().
         codec: Audio codec name (e.g., 'opus', 'aac', 'mp3') as returned by get_audio_codec().
 
     Returns:
@@ -22,37 +31,13 @@ def determine_default_format(container: Optional[str], codec: Optional[str]) ->
     if not container:
         return None
 
-    # Codec-based decisions (highest priority)
+    if codec and codec in CODEC_TO_CONTAINER_MAP:
-    if codec == 'opus':
+        fmt = CODEC_TO_CONTAINER_MAP[codec]
-        return 'opus'
+        if fmt in CONTAINER_NAMES:
-    if codec in ('aac', 'alac', 'he-aac'):
+            return fmt
-        return 'm4a'
-    if codec == 'mp3':
-        return 'mp3'
-    if codec == 'vorbis':
-        return 'ogg'
-    if codec == 'flac':
-        return 'flac'
 
-    # Container-based fallback (lower priority)
+    if container in CONTAINER_NAMES:
-    if container in ('mp4', 'm4a', 'mov', '3gp'):
+        return container
-        return 'mp4'
-    if container in ('matroska', 'webm'):
-        return 'matroska'
-    if container in ('ogg',):
-        return 'ogg'
-    if container in ('mp3', 'mpeg'):
-        return 'mp3'
-    if container == 'flac':
-        return 'flac'
-    if container == 'wav':
-        return 'wav'
-    if container == 'aac':
-        return 'aac'
-    if container == 'opus':
-        return 'opus'
-    if container == 'amr':
-        return 'amr'
 
     return None
 
@@ -62,69 +47,91 @@ def determine_output_format(stream_info: Dict, user_format: Optional[str],
     """
     Decide which container format to use.
 
-    If user_format is provided, use it.
+    If user_format is provided, map it to the correct container if it's a codec name.
     Else, try to detect the input file's container and codec, and use the recommended format.
     If detection fails or format is not supported, fallback to:
       - MKV if video/subtitles exist
       - MP3 if the audio codec is MP3
       - MP4 (M4A) otherwise
-
-    Args:
-        stream_info: Dict from get_stream_info().
-        user_format: User‑requested format (or None).
-        transcode_audio: Audio codec to transcode to (or None) (unused in this function).
-        input_file: Path to the input file (optional, used to detect container and codec).
-
-    Returns:
-        A format name that exists in FORMAT_INFO.
     """
     if user_format:
+        # Map codec names to their correct containers
+        # e.g., 'opus' -> 'ogg', 'aac' -> 'mp4', etc.
+        if user_format in CODEC_TO_CONTAINER_MAP:
+            return CODEC_TO_CONTAINER_MAP[user_format]
         return user_format
 
-    # If input_file is provided, try to detect container and codec
     if input_file:
         try:
             from .ffmpeg import get_container_format, get_audio_codec
             container = get_container_format(input_file)
-            codec = get_audio_codec(input_file)
+            audio_codec = get_audio_codec(input_file)
-            fmt = determine_default_format(container, codec)
+            fmt = determine_default_format(container, audio_codec)
-            if fmt in FORMAT_INFO:
+            if fmt in CONTAINER_NAMES:
                 return fmt
         except Exception:
-            # If detection fails, fall through to legacy logic
             pass
 
-    # Fallback: legacy behavior
+    # Fallback
     if stream_info.get('has_video') or stream_info.get('has_subtitle'):
-        return 'matroska'
+        return 'mkv'
     audio_codec = stream_info.get('audio_codec', '')
     if audio_codec == 'mp3':
         return 'mp3'
     else:
-        return 'mp4'  # .m4a
+        return 'mp4'
 
 
-def validate_format_compatibility(format_name: str, stream_info: Dict,
+def validate_format_compatibility(
-                                  drop_video: bool, drop_subs: bool) -> None:
+    container: str,
+    stream_info: Dict,
+    drop_video: bool,
+    drop_subs: bool,
+    input_file: Optional[str] = None,
+    audio_codec: Optional[str] = None,
+    video_codec: Optional[str] = None,
+) -> None:
     """
-    Ensure the chosen container can accommodate the streams we intend to keep.
+    Ensure the chosen container and codec combination is valid.
 
     Raises:
-        ValueError: If the format is incompatible with the intended streams.
+        ValueError: If the combination is incompatible.
     """
-    info = FORMAT_INFO.get(format_name)
+    info = next((c for c in CONTAINER_INFO if c['name'] == container), None)
     if not info:
-        print(f"Warning: Unknown format '{format_name}'. Proceeding, but may fail.")
+        print(f"Warning: Unknown container '{container}'. Proceeding, but may fail.")
         return
 
-    if info['audio_only']:
+    # Check if container is audio-only and video is present (unless dropped)
+    if not info['supports_video'] and stream_info.get('has_video') and not drop_video:
+        raise ValueError(
+            f"Container '{container}' does not support video streams. "
+            "Please use --drop-video or choose a container that supports video (e.g., MKV, MP4)."
+        )
+
+    # Determine actual audio codec for validation
+    # When 'copy' is used, we must still validate the input codec against the container
+    actual_audio_codec = audio_codec if audio_codec and audio_codec != 'copy' else stream_info.get('audio_codec')
+    if actual_audio_codec:
+        if not is_audio_codec_supported(container, actual_audio_codec):
+            raise ValueError(
+                f"Container '{container}' does not support audio codec '{actual_audio_codec}'. "
+                f"Please choose a different container or audio codec."
+            )
+
+    # Check if video codec is supported (if video is present and not dropped)
     if stream_info.get('has_video') and not drop_video:
+        # Determine the video codec from input file if not provided
+        if video_codec is None and input_file:
+            from .ffmpeg import get_video_codec
+            video_codec = get_video_codec(input_file)
+        # When 'copy' is used, validate the input video codec against the container
+        if video_codec == 'copy' and input_file:
+            from .ffmpeg import get_video_codec
+            video_codec = get_video_codec(input_file)
+        if video_codec:
+            if not is_video_codec_supported(container, video_codec):
                 raise ValueError(
-                f"Format '{format_name}' does not support video streams. "
+                    f"Container '{container}' does not support video codec '{video_codec}'. "
-                "Please use --drop-video or choose a container that supports video."
+                    f"Please choose a different container, drop video, or transcode video to a supported codec."
-            )
-        if stream_info.get('has_subtitle') and not drop_subs:
-            raise ValueError(
-                f"Format '{format_name}' does not support subtitle streams. "
-                "Please use --drop-subs or choose a container that supports subtitles."
                 )

audio_splitter/handlers.py

@@ -0,0 +1,167 @@
+# audio_splitter/handlers.py
+"""Handler system for cover image attachment.
+
+This module provides a registry of handlers for different
+codec + image combinations. Each handler is responsible for
+attaching the cover image to the output file in the appropriate way.
+"""
+
+import os
+import subprocess
+from typing import Dict, Optional
+
+
+def _run_opustags(input_file: str, cover_image_path: str, output_path: Optional[str] = None) -> bool:
+    """
+    Run opustags to attach a cover image to an Opus file.
+
+    Args:
+        input_file: Path to the input Opus file.
+        cover_image_path: Path to the cover image.
+        output_path: Optional output path (if None, overwrites input).
+
+    Returns:
+        True if successful, False otherwise.
+    """
+    cmd = ['opustags', '--set-cover', cover_image_path, input_file]
+
+    if output_path:
+        cmd.extend(['-o', output_path, '-y'])
+    else:
+        cmd.extend(['-i'])
+
+    result = subprocess.run(cmd, capture_output=True, text=True, check=False)
+    if result.returncode != 0:
+        print(f"opustags failed: {result.stderr}")
+        return False
+    return True
+
+
+def _handler_default(
+    input_file: str,
+    cover_image_path: str,
+    output_path: str,
+    stream_info: Dict,
+    audio_codec: str,
+    video_codec: str,
+    video_quality: Optional[int],
+    drop_video: bool,
+    drop_subs: bool,
+) -> bool:
+    """
+    Default handler: use ffmpeg with -disposition attached_pic.
+
+    This is the standard approach for formats like MP3, FLAC, etc.
+    """
+    # This handler doesn't do anything - the cover is already handled
+    # by the ffmpeg command in core.py via build_ffmpeg_command()
+    # We just return True to indicate success.
+    return True
+
+
+def _handler_opus_with_cover(
+    input_file: str,
+    cover_image_path: str,
+    output_path: str,
+    stream_info: Dict,
+    audio_codec: str,
+    video_codec: str,
+    video_quality: Optional[int],
+    drop_video: bool,
+    drop_subs: bool,
+) -> bool:
+    """
+    Handler for Opus files with cover image.
+
+    Uses opustags to attach the cover image after the file is processed.
+    """
+    return _run_opustags(output_path, cover_image_path)
+
+
+def _handler_mp3_with_cover(
+    input_file: str,
+    cover_image_path: str,
+    output_path: str,
+    stream_info: Dict,
+    audio_codec: str,
+    video_codec: str,
+    video_quality: Optional[int],
+    drop_video: bool,
+    drop_subs: bool,
+) -> bool:
+    """
+    Handler for MP3 files with cover image.
+
+    Uses ffmpeg with -disposition attached_pic.
+    """
+    # MP3 handler - the cover is already attached by ffmpeg in core.py
+    return True
+
+
+def _handler_flac_with_cover(
+    input_file: str,
+    cover_image_path: str,
+    output_path: str,
+    stream_info: Dict,
+    audio_codec: str,
+    video_codec: str,
+    video_quality: Optional[int],
+    drop_video: bool,
+    drop_subs: bool,
+) -> bool:
+    """
+    Handler for FLAC files with cover image.
+
+    Uses ffmpeg with -disposition attached_pic.
+    """
+    # FLAC handler - the cover is already attached by ffmpeg in core.py
+    return True
+
+
+# Handler registry: maps (output_container, input_codec) to handler function
+HANDLER_REGISTRY: Dict[tuple, callable] = {
+    ('opus', 'opus'): _handler_opus_with_cover,
+    ('ogg', 'opus'): _handler_opus_with_cover,
+    ('mp3', 'mp3'): _handler_mp3_with_cover,
+    ('flac', 'flac'): _handler_flac_with_cover,
+}
+
+
+def get_handler(output_container: str, input_audio_codec: Optional[str] = None):
+    """
+    Get the appropriate handler for the given container and input codec.
+
+    Args:
+        output_container: Output container format (e.g., 'opus', 'mp3', 'flac').
+        input_audio_codec: Input audio codec (e.g., 'opus', 'mp3', 'flac').
+
+    Returns:
+        Handler function, or the default handler if no specific handler is found.
+    """
+    if input_audio_codec:
+        key = (output_container, input_audio_codec)
+        if key in HANDLER_REGISTRY:
+            return HANDLER_REGISTRY[key]
+
+    # Fall back to container-only key
+    if (output_container, None) in HANDLER_REGISTRY:
+        return HANDLER_REGISTRY[(output_container, None)]
+
+    # Default handler
+    return _handler_default
+
+
+def needs_drop_video(output_container: str, input_audio_codec: Optional[str] = None) -> bool:
+    """
+    Check if the handler requires dropping video even if user didn't specify --drop-video.
+
+    Args:
+        output_container: Output container format.
+        input_audio_codec: Input audio codec.
+
+    Returns:
+        True if video should be dropped, False otherwise.
+    """
+    handler = get_handler(output_container, input_audio_codec)
+    # The opus handler requires dropping video
+    return handler == _handler_opus_with_cover

audio_splitter/main.py

@@ -1,11 +1,18 @@
-"""Command‑line interface and entry point."""
+#!/usr/bin/env python3
+"""
+Audio Splitter – Command‑Line Interface
+
+Split an audio file into tracks using a tracklist file.
+
+Usage:
+    audio_splitter input.mp3 tracklist.txt [OPTIONS]
+"""
 
-import argparse
 import os
 import sys
 import subprocess
+import argparse
 
-from .constants import DEFAULT_BAD_CHARS
 from .defaults import (
     DEFAULT_FORMAT,
     DEFAULT_OUTPUT_TEMPLATE,
@@ -24,50 +31,164 @@ from .defaults import (
     DEFAULT_REPLACE_BAD_CHARS,
     DEFAULT_SKIP_EXISTING,
     DEFAULT_DELETE_ORIGINAL,
-    DEFAULT_TRANSCODE_TO,
 )
+from .constants import CONTAINER_NAMES
 from .core import split_audio
 from .tracklist import read_tracklist, parse_format
+from .ffmpeg import has_cover_or_video, validate_cover_images
+
 
 def main():
-    parser = argparse.ArgumentParser(description="Split audio file using a tracklist.")
+    parser = argparse.ArgumentParser(
+        description="Split an audio file into tracks using a tracklist.",
+        epilog="Tracklist format: mm:ss track_name - author_name (or custom with --tracklist-format)"
+    )
+
+    # Positional
     parser.add_argument('input_file', help='Input audio file')
     parser.add_argument('tracklist_file', help='Tracklist file')
 
-    # Output options
+    # Container and codec options
-    parser.add_argument('--format', default=DEFAULT_FORMAT, help=f"Output container format (default: {DEFAULT_FORMAT})")
+    parser.add_argument(
-    parser.add_argument('--transcode-to', default=DEFAULT_TRANSCODE_TO, help="Audio codec to transcode to (default: copy)")
+        '--container',
-    parser.add_argument('--drop-video', action='store_true', default=DEFAULT_DROP_VIDEO, help="Drop video streams")
+        default=None,
-    parser.add_argument('--drop-subs', action='store_true', default=DEFAULT_DROP_SUBS, help="Drop subtitle streams")
+        help="Output container format (auto-detect if not specified)"
+    )
+    parser.add_argument(
+        '--audio-codec',
+        default='copy',
+        help="Audio codec (copy or encoder name, e.g., libopus)"
+    )
+    parser.add_argument(
+        '--video-codec',
+        default='copy',
+        help="Video codec (copy or encoder name, e.g., libx264)"
+    )
+    parser.add_argument(
+        '--subtitle-codec',
+        default='copy',
+        help="Subtitle codec (copy or encoder name, e.g., srt)"
+    )
+    parser.add_argument(
+        '--video-quality', '-vq',
+        type=int,
+        default=None,
+        help="Video quality (integer, encoder-specific; usually 1-31, lower=better). "
+             "If omitted, FFmpeg default is used."
+    )
+    parser.add_argument(
+        '--drop-video',
+        action='store_true',
+        default=DEFAULT_DROP_VIDEO,
+        help="Drop video streams"
+    )
+    parser.add_argument(
+        '--drop-subs',
+        action='store_true',
+        default=DEFAULT_DROP_SUBS,
+        help="Drop subtitle streams"
+    )
 
     # Filename options
-    parser.add_argument('--number-tracks', action='store_true', default=DEFAULT_NUMBER_TRACKS, help="Prepend track numbers")
+    parser.add_argument(
-    parser.add_argument('--output-template', default=DEFAULT_OUTPUT_TEMPLATE, help=f"Output filename template (default: {DEFAULT_OUTPUT_TEMPLATE})")
+        '--number-tracks',
-    parser.add_argument('--replace-bad-chars', action='store_true', default=DEFAULT_REPLACE_BAD_CHARS, help="Replace bad characters")
+        action='store_true',
-    parser.add_argument('--replacement-char', default=DEFAULT_REPLACEMENT_CHAR, help=f"Replacement character (default: {DEFAULT_REPLACEMENT_CHAR})")
+        default=DEFAULT_NUMBER_TRACKS,
-    parser.add_argument('--bad-chars', default=DEFAULT_BAD_CHARS, help=f"Bad characters to replace (default: {DEFAULT_BAD_CHARS})")
+        help="Prepend track numbers"
-    parser.add_argument('--skip-existing', action='store_true', default=DEFAULT_SKIP_EXISTING, help="Skip existing output files")
+    )
+    parser.add_argument(
+        '--output-template',
+        default=DEFAULT_OUTPUT_TEMPLATE,
+        help="Output filename template (default: %(default)s)"
+    )
+    parser.add_argument(
+        '--replace-bad-chars',
+        action='store_true',
+        default=DEFAULT_REPLACE_BAD_CHARS,
+        help="Replace bad characters"
+    )
+    parser.add_argument(
+        '--replacement-char',
+        default=DEFAULT_REPLACEMENT_CHAR,
+        help="Replacement character (default: %(default)s)"
+    )
+    parser.add_argument(
+        '--bad-chars',
+        default=DEFAULT_BAD_CHARS,
+        help="Bad characters to replace (default: %(default)s)"
+    )
+    parser.add_argument(
+        '--skip-existing',
+        action='store_true',
+        default=DEFAULT_SKIP_EXISTING,
+        help="Skip existing output files"
+    )
 
-    # Metadata options
+    # Metadata
     parser.add_argument('--album', default=DEFAULT_ALBUM, help="Album name")
     parser.add_argument('--comment', default=DEFAULT_COMMENT, help="Comment")
-    parser.add_argument('--no-comment', action='store_true', default=DEFAULT_NO_COMMENT, help="Ignore comment")
+    parser.add_argument(
-    parser.add_argument('--comment-stream', type=int, default=DEFAULT_COMMENT_STREAM, help="Comment stream index")
+        '--no-comment',
-    parser.add_argument('--merge-comments', action='store_true', default=DEFAULT_MERGE_COMMENTS, help="Merge all comments")
+        action='store_true',
-    parser.add_argument('--comment-separator', default=DEFAULT_COMMENT_SEPARATOR, help=f"Separator for merged comments (default: {DEFAULT_COMMENT_SEPARATOR})")
+        default=DEFAULT_NO_COMMENT,
+        help="Ignore comment"
+    )
+    parser.add_argument(
+        '--comment-stream',
+        type=int,
+        default=DEFAULT_COMMENT_STREAM,
+        help="Comment stream index"
+    )
+    parser.add_argument(
+        '--merge-comments',
+        action='store_true',
+        default=DEFAULT_MERGE_COMMENTS,
+        help="Merge all comments"
+    )
+    parser.add_argument(
+        '--comment-separator',
+        default=DEFAULT_COMMENT_SEPARATOR,
+        help="Separator for merged comments (default: %(default)s)"
+    )
 
     # Tracklist format
-    parser.add_argument('--tracklist-format', default=DEFAULT_TRACKLIST_FORMAT, help=f"Tracklist format (default: {DEFAULT_TRACKLIST_FORMAT})")
+    parser.add_argument(
+        '--tracklist-format',
+        default=DEFAULT_TRACKLIST_FORMAT,
+        help="Tracklist format (default: %(default)s)"
+    )
+
+    # Cover image
+    parser.add_argument(
+        '--cover-image',
+        nargs='+',
+        metavar='IMAGE',
+        default=None,
+        help="Cover image path(s). Single image applied to all tracks, "
+             "or one per track (must match track count)."
+    )
 
     # Other
-    parser.add_argument('--delete-original', action='store_true', default=DEFAULT_DELETE_ORIGINAL, help="Delete original file after split")
+    parser.add_argument(
-    parser.add_argument('--dry-run', action='store_true', help="Parse and display tracklist without splitting")
+        '--delete-original',
+        action='store_true',
+        default=DEFAULT_DELETE_ORIGINAL,
+        help="Delete original file after split"
+    )
+    parser.add_argument(
+        '--dry-run',
+        action='store_true',
+        help="Parse and display tracklist without splitting"
+    )
+    parser.add_argument(
+        '--output-dir', '-o',
+        default=None,
+        help="Output directory (default: <input_basename>_splits)"
+    )
 
     args = parser.parse_args()
 
-    # --------------------------------------------------------------------------
+    # Validate input
-    # Input validation
-    # --------------------------------------------------------------------------
     if not os.path.exists(args.input_file):
         print(f"Error: Input file not found: {args.input_file}")
         sys.exit(1)
@@ -76,12 +197,13 @@ def main():
         print(f"Error: Tracklist file not found: {args.tracklist_file}")
         sys.exit(1)
 
-    # Ensure the replacement character is a single character.
+    # Validate container if provided
-    if len(args.replacement_char) != 1:
+    if args.container and args.container not in CONTAINER_NAMES:
-        print("Error: --replacement-char must be a single character.")
+        print(f"Error: Invalid container '{args.container}'. "
+              f"Valid containers: {', '.join(sorted(CONTAINER_NAMES))}.")
         sys.exit(1)
 
-    # Check that FFmpeg is installed.
+    # Check FFmpeg
     try:
         subprocess.run(['ffmpeg', '-version'], capture_output=True, check=True)
     except (subprocess.CalledProcessError, FileNotFoundError):
@@ -89,14 +211,14 @@ def main():
         print("  - https://ffmpeg.org/download.html")
         sys.exit(1)
 
-    # Parse the tracklist using the user‑provided format.
+    # Parse tracklist format
     try:
         tokens = parse_format(args.tracklist_format)
-    except ValueError as error:
+    except ValueError as e:
-        print(f"Error in --tracklist-format: {error}")
+        print(f"Error in --tracklist-format: {e}")
         sys.exit(1)
 
-    # Read and parse the tracklist file.
+    # Read tracklist
     tracks = read_tracklist(args.tracklist_file, tokens)
     if not tracks:
         print("Error: No valid tracks found in tracklist file.")
@@ -104,7 +226,21 @@ def main():
 
     print(f"Found {len(tracks)} tracks.")
 
-    # Dry‑run mode: display parsed data and exit.
+    # Validate cover images if provided
+    if args.cover_image:
+        # Check if input already has cover image or video track
+        # Allow if --drop-video is specified (user wants to discard existing video)
+        if has_cover_or_video(args.input_file) and not args.drop_video:
+            print("Error: Input file already contains a cover image or video track. "
+                  "Remove it first, or use --drop-video to discard video streams.")
+            sys.exit(1)
+
+        try:
+            validate_cover_images(args.cover_image, len(tracks))
+        except ValueError as e:
+            print(f"Error: {e}")
+            sys.exit(1)
+
     if args.dry_run:
         print("\nParsed tracklist:")
         print("-" * 60)
@@ -118,34 +254,22 @@ def main():
                 print(f"{idx:3d} | " + " | ".join(values))
         print("-" * 60)
         print("Dry‑run complete. No files were created.")
-        sys.exit(0)
+        return
 
-    # Determine the output directory.
+    # Determine output directory
     if args.output_dir:
         output_dir = args.output_dir
-        print(f"Using custom output directory: {output_dir}")
     else:
         base_name = os.path.splitext(os.path.basename(args.input_file))[0]
         output_dir = base_name + "_splits"
-        print(f"Using default output directory: {output_dir}")
 
-    # Run the splitter.
+    # Run split
     try:
         split_audio(args.input_file, output_dir, tracks, args)
-    except (RuntimeError, ValueError) as error:
+    except Exception as e:
-        print(f"Error: {error}")
+        print(f"Error during split: {e}")
         sys.exit(1)
 
-    # --------------------------------------------------------------------------
-    # Delete original file if requested and successful.
-    # --------------------------------------------------------------------------
-    if args.delete_original:
-        try:
-            os.remove(args.input_file)
-            print(f"Deleted original file: {args.input_file}")
-        except OSError as e:
-            print(f"Warning: Could not delete original file: {e}")
-
     print("Done!")
 
 

audio_splitter/timestamp.py

@@ -73,4 +73,15 @@ def resolve_end_times(track_times, total_duration):
             if end_sec <= start_sec:
                 raise ValueError(f"Track {idx+1}: end time ({end_sec}) is not after start ({start_sec})")
         resolved.append((start_sec, end_sec))
+
+    # Warn about overlapping intervals
+    for idx in range(len(resolved) - 1):
+        cur_end = resolved[idx][1]
+        next_start = resolved[idx + 1][0]
+        if cur_end > next_start:
+            print(
+                f"Warning: Track {idx+1} ends at {cur_end}s but Track {idx+2} starts at "
+                f"{next_start}s — timestamps overlap by {cur_end - next_start:.1f}s."
+            )
+
     return resolved

web/backend/Dockerfile

@@ -1,9 +1,10 @@
 FROM python:3.13-slim
 
-# Install FFmpeg, system dependencies, and gosu from APT
+# Install FFmpeg, opustags, system dependencies, and gosu from APT
 RUN apt-get update && \
     apt-get install -y --no-install-recommends \
         ffmpeg \
+        opustags \
         ca-certificates \
         gosu \
         && \

web/backend/api/__init__.py

@@ -1,3 +1,3 @@
 """API route handlers."""
 
-from . import upload, split, split_file, status, download, formats, info
+from . import upload, split, split_file, status, download, websocket, formats, info

web/backend/api/formats.py

@@ -1,8 +1,9 @@
+# web/backend/api/formats.py
 """Endpoint to expose format information to the frontend."""
 
 from fastapi import APIRouter
 
-from backend.constants import FORMAT_INFO
+from audio_splitter.constants import CONTAINER_INFO, CODEC_INFO, COMPATIBILITY_MATRIX
 
 router = APIRouter(prefix="/api", tags=["formats"])
 
@@ -10,16 +11,10 @@ router = APIRouter(prefix="/api", tags=["formats"])
 @router.get("/formats")
 async def get_formats():
     """
-    Return the list of supported container formats with their properties.
+    Return the list of supported containers, codecs, and compatibility matrix.
     """
     return {
-        "formats": [
+        "containers": CONTAINER_INFO,
-            {
+        "codecs": CODEC_INFO,
-                "name": name,
+        "compatibility": COMPATIBILITY_MATRIX,
-                "ffmpeg": info["ffmpeg"],
-                "extension": info["ext"],
-                "audio_only": info["audio_only"],
-            }
-            for name, info in FORMAT_INFO.items()
-        ]
     }

web/backend/api/info.py

@@ -9,7 +9,7 @@ from backend.services.task_manager import task_manager
 # Import core functions
 from audio_splitter.ffmpeg import get_stream_info, get_container_format, get_audio_codec
 from audio_splitter.formats import determine_default_format
-from audio_splitter.constants import FORMAT_INFO
+from audio_splitter.constants import CONTAINER_NAMES
 from audio_splitter.defaults import DEFAULT_FORMAT
 
 router = APIRouter(prefix="/api", tags=["info"])
@@ -63,7 +63,7 @@ async def get_recommended_format(task_id: str):
         # Fallback if detection fails or format is unsupported
         if fmt is None:
             fmt = DEFAULT_FORMAT
-        if fmt not in FORMAT_INFO:
+        if fmt not in CONTAINER_NAMES:
             fmt = "mp3"  # ultimate fallback
 
         return {"format": fmt}

web/backend/api/split.py

@@ -1,4 +1,4 @@
-"""Split task endpoint."""
+"""Split task endpoint (JSON tracklist)."""
 
 from fastapi import APIRouter, HTTPException, BackgroundTasks
 
@@ -24,6 +24,29 @@ async def start_split(request: SplitRequest, background_tasks: BackgroundTasks):
             detail=f"Task {task_id} is already {status['status']}"
         )
 
+    # Build options dict from request
+    options = {
+        "container": request.container,
+        "audio_codec": request.audio_codec,
+        "video_codec": request.video_codec,
+        "subtitle_codec": request.subtitle_codec,
+        "video_quality": request.video_quality,
+        "drop_video": request.drop_video,
+        "drop_subs": request.drop_subs,
+        "number_tracks": request.number_tracks,
+        "replace_bad_chars": request.replace_bad_chars,
+        "replacement_char": request.replacement_char,
+        "bad_chars": request.bad_chars,
+        "skip_existing": request.skip_existing,
+        "output_template": request.output_template,
+        "album": request.album,
+        "comment": request.comment,
+        "no_comment": request.no_comment,
+        "comment_stream": request.comment_stream,
+        "merge_comments": request.merge_comments,
+        "comment_separator": request.comment_separator,
+    }
+
     task_manager.update_task(
         task_id,
         status=TaskStatus.PROCESSING,
@@ -31,7 +54,12 @@ async def start_split(request: SplitRequest, background_tasks: BackgroundTasks):
         message="Preparing to split..."
     )
 
-    background_tasks.add_task(run_split_task, task_id, request.tracklist, request.options)
+    background_tasks.add_task(
+        run_split_task,
+        task_id,
+        request.tracklist,
+        options
+    )
 
     return SplitResponse(
         task_id=task_id,

web/backend/api/split_file.py

@@ -2,6 +2,7 @@
 
 import json
 from pathlib import Path
+from typing import Optional
 
 from fastapi import APIRouter, UploadFile, File, Form, HTTPException, BackgroundTasks
 
@@ -13,7 +14,6 @@ from backend.models.response import SplitResponse, TaskStatus
 
 router = APIRouter(prefix="/api", tags=["split"])
 
-# Import CLI tracklist parsing functions
 from audio_splitter.tracklist import parse_format, read_tracklist
 
 
@@ -22,29 +22,33 @@ async def split_from_file(
     background_tasks: BackgroundTasks,
     task_id: str = Form(...),
     tracklist_file: UploadFile = File(...),
-    options: str = Form("{}"),
+    # New fields
+    container: Optional[str] = Form(None),
+    audio_codec: str = Form("copy"),
+    video_codec: str = Form("copy"),
+    subtitle_codec: str = Form("copy"),
+    video_quality: Optional[int] = Form(None),
+    drop_video: bool = Form(False),
+    drop_subs: bool = Form(False),
+    number_tracks: bool = Form(False),
+    replace_bad_chars: bool = Form(False),
+    replacement_char: str = Form("_"),
+    bad_chars: str = Form(r'!@#№$;:%^&?*(){}[]\/<>+=~`\' '),
+    skip_existing: bool = Form(False),
+    output_template: str = Form("%an-%tn.%ext"),
+    album: Optional[str] = Form(None),
+    comment: Optional[str] = Form(None),
+    no_comment: bool = Form(False),
+    comment_stream: Optional[int] = Form(None),
+    merge_comments: bool = Form(False),
+    comment_separator: str = Form("; "),
+    options: str = Form("{}"),  # backward-compatible, but we now use explicit fields
     tracklist_format: str = Form("%ts %tn - %an"),
 ):
-    """
-    Start a splitting task using a tracklist file.
-
-    This endpoint accepts a plain text tracklist file (like the CLI does)
-    and parses it using the same logic.
-
-    Args:
-        task_id: Task ID from upload.
-        tracklist_file: Tracklist file (text/plain).
-        options: JSON string of all CLI options.
-        tracklist_format: Format string for parsing (default: "%ts %tn - %an").
-
-    Returns:
-        SplitResponse with task_id and status.
-    """
     # Validate task exists
     if not task_manager.has_task(task_id):
         raise HTTPException(status_code=404, detail=f"Task {task_id} not found")
 
-    # Check if task is already processing
     status = task_manager.get_status(task_id)
     if status and status["status"] in (TaskStatus.PROCESSING, TaskStatus.DONE):
         raise HTTPException(
@@ -52,14 +56,12 @@ async def split_from_file(
             detail=f"Task {task_id} is already {status['status']}"
         )
 
-    # Validate file type
     if not tracklist_file.filename.endswith(('.txt', '.text')):
         raise HTTPException(
             status_code=400,
             detail="Tracklist file must be a text file (.txt or .text)"
         )
 
-    # Read and parse the tracklist file
     try:
         content = await tracklist_file.read()
         text = content.decode('utf-8')
@@ -75,17 +77,13 @@ async def split_from_file(
             detail="Tracklist file is empty"
         )
 
-    # Parse the tracklist using CLI logic
+    # Parse tracklist using CLI logic
     try:
-        # Parse the format string into tokens
         tokens = parse_format(tracklist_format)
-
-        # Write the content to a temporary file (read_tracklist expects a file path)
         temp_tracklist_path = settings.temp_dir / task_id / "tracklist.txt"
         temp_tracklist_path.parent.mkdir(parents=True, exist_ok=True)
         temp_tracklist_path.write_text(text, encoding='utf-8')
 
-        # Parse the tracklist file using CLI logic
         tracklist_dicts = read_tracklist(str(temp_tracklist_path), tokens)
 
     except Exception as e:
@@ -100,7 +98,7 @@ async def split_from_file(
             detail="No valid tracks found in tracklist file"
         )
 
-    # Convert dicts to TracklistEntry objects (same as JSON endpoint)
+    # Convert dicts to TracklistEntry objects
     try:
         tracklist_entries = [TracklistEntry(**entry) for entry in tracklist_dicts]
     except Exception as e:
@@ -109,14 +107,28 @@ async def split_from_file(
             detail=f"Invalid tracklist data: {str(e)}"
         )
 
-    # Parse options JSON
+    # Build options dict from explicit fields (ignore `options` parameter)
-    try:
+    options = {
-        options_dict = json.loads(options)
+        "container": container,
-    except json.JSONDecodeError:
+        "audio_codec": audio_codec,
-        raise HTTPException(
+        "video_codec": video_codec,
-            status_code=400,
+        "subtitle_codec": subtitle_codec,
-            detail="Invalid JSON in options field"
+        "video_quality": video_quality,
-        )
+        "drop_video": drop_video,
+        "drop_subs": drop_subs,
+        "number_tracks": number_tracks,
+        "replace_bad_chars": replace_bad_chars,
+        "replacement_char": replacement_char,
+        "bad_chars": bad_chars,
+        "skip_existing": skip_existing,
+        "output_template": output_template,
+        "album": album,
+        "comment": comment,
+        "no_comment": no_comment,
+        "comment_stream": comment_stream,
+        "merge_comments": merge_comments,
+        "comment_separator": comment_separator,
+    }
 
     # Update task status
     task_manager.update_task(
@@ -126,12 +138,11 @@ async def split_from_file(
         message="Preparing to split..."
     )
 
-    # Start background task
     background_tasks.add_task(
         run_split_task,
         task_id,
-        tracklist_entries,  # now TracklistEntry objects
+        tracklist_entries,
-        options_dict
+        options
     )
 
     return SplitResponse(

web/backend/api/upload.py

@@ -14,7 +14,8 @@ router = APIRouter(prefix="/api", tags=["upload"])
 
 ALLOWED_EXTENSIONS = {
     ".mp3", ".flac", ".wav", ".m4a", ".ogg", ".opus",
-    ".aac", ".wma", ".aiff", ".alac", ".ac3"
+    ".aac", ".wma", ".aiff", ".alac", ".ac3",
+    ".mp4", ".mkv", ".webm",
 }
 
 

web/backend/constants.py

@@ -1,12 +0,0 @@
-FORMAT_INFO = {
-    'mp3':      {'ffmpeg': 'mp3',      'ext': '.mp3',  'audio_only': True},
-    'm4a':      {'ffmpeg': 'mp4',      'ext': '.m4a',  'audio_only': True},
-    'mp4':      {'ffmpeg': 'mp4',      'ext': '.mp4',  'audio_only': False},
-    'mkv':      {'ffmpeg': 'matroska', 'ext': '.mkv',  'audio_only': False},
-    'matroska': {'ffmpeg': 'matroska', 'ext': '.mkv',  'audio_only': False},
-    'ogg':      {'ffmpeg': 'ogg',      'ext': '.ogg',  'audio_only': True},
-    'opus':     {'ffmpeg': 'ogg',      'ext': '.opus', 'audio_only': True},
-    'flac':     {'ffmpeg': 'flac',     'ext': '.flac', 'audio_only': True},
-    'wav':      {'ffmpeg': 'wav',      'ext': '.wav',  'audio_only': True},
-    'aac':      {'ffmpeg': 'adts',     'ext': '.aac',  'audio_only': True},
-}

web/backend/models/request.py

@@ -17,19 +17,16 @@ class TracklistEntry(BaseModel):
 
     @validator("ts")
     def validate_timestamp(cls, v: str) -> str:
-        """Basic timestamp validation (format and range)."""
         v = v.strip()
         if not v:
             raise ValueError("Timestamp cannot be empty")
 
-        # Check for range format (start-end)
         if "-" in v:
             parts = v.split("-", 1)
             start = parts[0].strip()
             end = parts[1].strip()
             if not start or not end:
                 raise ValueError("Invalid range format. Expected 'start-end'")
-            # Validate each part with the same logic
             for ts in [start, end]:
                 cls._validate_single_timestamp(ts)
         else:
@@ -39,7 +36,6 @@ class TracklistEntry(BaseModel):
 
     @staticmethod
     def _validate_single_timestamp(ts: str) -> None:
-        """Validate a single timestamp (mm:ss or HH:MM:SS)."""
         parts = ts.split(":")
         if len(parts) not in (2, 3):
             raise ValueError(f"Invalid timestamp format: {ts}. Expected mm:ss or HH:MM:SS")
@@ -55,4 +51,30 @@ class SplitRequest(BaseModel):
 
     task_id: str = Field(..., description="Task ID from upload")
     tracklist: List[TracklistEntry] = Field(..., description="List of tracks")
-    options: dict = Field(default_factory=dict, description="All CLI options")
+
+    # Container and codec options
+    container: Optional[str] = Field(None, description="Output container (auto-detect if None)")
+    audio_codec: Optional[str] = Field("copy", description="Audio codec (copy or encoder name)")
+    video_codec: Optional[str] = Field("copy", description="Video codec (copy or encoder name)")
+    subtitle_codec: Optional[str] = Field("copy", description="Subtitle codec (copy or encoder name)")
+    video_quality: Optional[int] = Field(None, description="Video quality (encoder-specific integer)")
+
+    # Stream handling
+    drop_video: bool = Field(False, description="Remove video streams")
+    drop_subs: bool = Field(False, description="Remove subtitle streams")
+
+    # Filename options
+    number_tracks: bool = Field(False, description="Prepend track numbers")
+    replace_bad_chars: bool = Field(False, description="Replace bad characters")
+    replacement_char: str = Field("_", description="Replacement character")
+    bad_chars: str = Field(r'!@#№$;:%^&?*(){}[]\/<>+=~`\' ', description="Bad characters to replace")
+    skip_existing: bool = Field(False, description="Skip existing files")
+    output_template: str = Field("%an-%tn.%ext", description="Output filename template")
+
+    # Metadata options
+    album: Optional[str] = Field(None, description="Album name")
+    comment: Optional[str] = Field(None, description="Comment")
+    no_comment: bool = Field(False, description="Ignore comment")
+    comment_stream: Optional[int] = Field(None, description="Comment stream index")
+    merge_comments: bool = Field(False, description="Merge all comments")
+    comment_separator: str = Field("; ", description="Separator for merged comments")

web/backend/services/splitter.py

@@ -2,10 +2,10 @@
 
 import os
 import sys
-import time
+import shutil
 from pathlib import Path
-from types import SimpleNamespace
+from typing import List, Dict, Any
-from typing import Dict, List, Any
+import time
 
 from backend.config import settings
 from backend.services.task_manager import task_manager
@@ -13,31 +13,12 @@ from backend.services.file_manager import FileManager
 from backend.models.request import TracklistEntry
 from backend.models.response import TaskStatus
 
-# Import central defaults
-from audio_splitter.defaults import (
-    DEFAULT_FORMAT,
-    DEFAULT_OUTPUT_TEMPLATE,
-    DEFAULT_REPLACEMENT_CHAR,
-    DEFAULT_BAD_CHARS,
-    DEFAULT_ALBUM,
-    DEFAULT_COMMENT,
-    DEFAULT_NO_COMMENT,
-    DEFAULT_COMMENT_STREAM,
-    DEFAULT_MERGE_COMMENTS,
-    DEFAULT_COMMENT_SEPARATOR,
-    DEFAULT_DROP_VIDEO,
-    DEFAULT_DROP_SUBS,
-    DEFAULT_NUMBER_TRACKS,
-    DEFAULT_REPLACE_BAD_CHARS,
-    DEFAULT_SKIP_EXISTING,
-    DEFAULT_DELETE_ORIGINAL,
-    DEFAULT_TRANSCODE_TO,
-)
-
 
 def run_split_task(task_id: str, tracklist: List[TracklistEntry], options: Dict[str, Any]) -> None:
     try:
-        task_manager.update_task_with_progress(task_id, progress=5, message="Initializing...")
+        task_manager.update_task_with_progress(
+            task_id, progress=5, message="Initializing..."
+        )
 
         input_path = FileManager.get_input_path(task_id)
         if not input_path or not input_path.exists():
@@ -45,7 +26,6 @@ def run_split_task(task_id: str, tracklist: List[TracklistEntry], options: Dict[
 
         output_dir = FileManager.ensure_output_dir(task_id)
 
-        # Convert tracklist to dicts (CLI format)
         tracks = []
         for entry in tracklist:
             track_dict = {
@@ -58,25 +38,30 @@ def run_split_task(task_id: str, tracklist: List[TracklistEntry], options: Dict[
             }
             tracks.append(track_dict)
 
-        # Build args namespace using defaults where options not provided
+        from types import SimpleNamespace
+
+        # Build args namespace using the new fields
         args = SimpleNamespace(
-            format=options.get("format", DEFAULT_FORMAT),
+            container=options.get("container"),  # None -> auto-detect
-            transcode_to=options.get("transcode_to", DEFAULT_TRANSCODE_TO),
+            audio_codec=options.get("audio_codec", "copy"),
-            drop_video=options.get("drop_video", DEFAULT_DROP_VIDEO),
+            video_codec=options.get("video_codec", "copy"),
-            drop_subs=options.get("drop_subs", DEFAULT_DROP_SUBS),
+            subtitle_codec=options.get("subtitle_codec", "copy"),
-            number_tracks=options.get("number_tracks", DEFAULT_NUMBER_TRACKS),
+            video_quality=options.get("video_quality"),
-            replace_bad_chars=options.get("replace_bad_chars", DEFAULT_REPLACE_BAD_CHARS),
+            drop_video=options.get("drop_video", False),
-            replacement_char=options.get("replacement_char", DEFAULT_REPLACEMENT_CHAR),
+            drop_subs=options.get("drop_subs", False),
-            bad_chars=options.get("bad_chars", DEFAULT_BAD_CHARS),
+            number_tracks=options.get("number_tracks", False),
-            skip_existing=options.get("skip_existing", DEFAULT_SKIP_EXISTING),
+            replace_bad_chars=options.get("replace_bad_chars", False),
-            output_template=options.get("output_template", DEFAULT_OUTPUT_TEMPLATE),
+            replacement_char=options.get("replacement_char", "_"),
-            album=options.get("album", DEFAULT_ALBUM),
+            bad_chars=options.get("bad_chars", r'!@#№$;:%^&?*(){}[]\/<>+=~`\' '),
-            comment=options.get("comment", DEFAULT_COMMENT),
+            skip_existing=options.get("skip_existing", False),
-            no_comment=options.get("no_comment", DEFAULT_NO_COMMENT),
+            output_template=options.get("output_template", "%an-%tn.%ext"),
-            comment_stream=options.get("comment_stream", DEFAULT_COMMENT_STREAM),
+            album=options.get("album", None),
-            merge_comments=options.get("merge_comments", DEFAULT_MERGE_COMMENTS),
+            comment=options.get("comment", None),
-            comment_separator=options.get("comment_separator", DEFAULT_COMMENT_SEPARATOR),
+            no_comment=options.get("no_comment", False),
-            delete_original=DEFAULT_DELETE_ORIGINAL,  # never delete in web
+            comment_stream=options.get("comment_stream", None),
+            merge_comments=options.get("merge_comments", False),
+            comment_separator=options.get("comment_separator", "; "),
+            delete_original=False,
         )
 
         project_root = Path(__file__).parent.parent.parent.parent
@@ -85,7 +70,13 @@ def run_split_task(task_id: str, tracklist: List[TracklistEntry], options: Dict[
 
         from audio_splitter.core import split_audio
 
-        task_manager.update_task_with_progress(task_id, progress=10, message="Starting split...")
+        # Cover image handling is now done internally by split_audio()
+        # via the handler system (opustags for Opus, ffmpeg for others)
+        args.cover_image = None
+
+        task_manager.update_task_with_progress(
+            task_id, progress=10, message="Starting split..."
+        )
 
         split_audio(str(input_path), str(output_dir), tracks, args)
 

web/frontend/src/App.tsx

@@ -68,16 +68,15 @@ const App: React.FC = () => {
     reset()
   }
 
-  const isSplitDisabled = !taskId || !isValid || entries.length === 0 || isProcessing || !!formatError
+  const isSplitDisabled =
+    !taskId ||
+    !isValid ||
+    entries.length === 0 ||
+    isProcessing ||
+    !!formatError
 
   return (
-    <ThemeProvider
+    <ThemeProvider theme={createTheme({ palette: { mode: theme } })}>
-      theme={createTheme({
-        palette: {
-          mode: theme,
-        },
-      })}
-    >
       <CssBaseline />
       <Layout>
         <Grid container spacing={3}>

web/frontend/src/api/client.ts

@@ -1,5 +1,12 @@
 import axios from 'axios'
-import { TracklistEntry, SplitOptions, TaskStatus } from '../types'
+import {
+  TracklistEntry,
+  SplitOptions,
+  TaskStatus,
+  FormatsResponse,
+  UploadResponse,
+  SplitResponse,
+} from '../types'
 
 export const api = axios.create({
   baseURL: '/api',
@@ -8,16 +15,14 @@ export const api = axios.create({
   },
 })
 
-export const uploadFile = async (file: File): Promise<{ task_id: string; filename: string; size: number }> => {
+export const uploadFile = async (file: File): Promise<UploadResponse> => {
   const formData = new FormData()
   formData.append('file', file)
-
   const response = await api.post('/upload', formData, {
     headers: {
       'Content-Type': 'multipart/form-data',
     },
   })
-
   return response.data
 }
 
@@ -25,12 +30,32 @@ export const startSplit = async (
   task_id: string,
   tracklist: TracklistEntry[],
   options: SplitOptions
-): Promise<{ task_id: string; status: string }> => {
+): Promise<SplitResponse> => {
-  const response = await api.post('/split', {
+  // Build request payload (only send fields that are not undefined)
+  const payload: any = {
     task_id,
     tracklist,
-    options,
+    container: options.container, // null means auto-detect
-  })
+    audio_codec: options.audio_codec,
+    video_codec: options.video_codec,
+    subtitle_codec: options.subtitle_codec,
+    video_quality: options.video_quality,
+    drop_video: options.drop_video,
+    drop_subs: options.drop_subs,
+    number_tracks: options.number_tracks,
+    replace_bad_chars: options.replace_bad_chars,
+    replacement_char: options.replacement_char,
+    bad_chars: options.bad_chars,
+    skip_existing: options.skip_existing,
+    output_template: options.output_template,
+    album: options.album || null,
+    comment: options.comment || null,
+    no_comment: options.no_comment,
+    comment_stream: options.comment_stream,
+    merge_comments: options.merge_comments,
+    comment_separator: options.comment_separator,
+  }
+  const response = await api.post('/split', payload)
   return response.data
 }
 
@@ -47,8 +72,7 @@ export const getDownloadZipUrl = (task_id: string): string => {
   return `/api/download/${task_id}/splits.zip`
 }
 
-// New functions for format validation feature
+export const getFormats = async (): Promise<FormatsResponse> => {
-export const getFormatInfo = async (): Promise<{ formats: Array<{ name: string; audio_only: boolean }> }> => {
   const response = await api.get('/formats')
   return response.data
 }

web/frontend/src/components/OptionsPanel.tsx

@@ -1,4 +1,4 @@
-import React, { useEffect } from 'react'
+import React, { useEffect, useMemo } from 'react'
 import {
   Box,
   Paper,
@@ -16,7 +16,14 @@ import { ExpandMore, ExpandLess } from '@mui/icons-material'
 import { useOptionsStore } from '../stores/optionsStore'
 import { useUploadStore } from '../stores/uploadStore'
 import { useValidationStore } from '../stores/validationStore'
+import { getFormats } from '../api/client'
+import { SplitOptions } from '../types'
+import { useFilterCodecs } from '../hooks/useFilterCodecs'
+import { useFormatValidation } from '../hooks/useFormatValidation'
 
+// ------------------------------------------------------------------------------
+// Section component (collapsible)
+// ------------------------------------------------------------------------------
 interface SectionProps {
   title: string
   children: React.ReactNode
@@ -25,7 +32,6 @@ interface SectionProps {
 
 const Section: React.FC<SectionProps> = ({ title, children, defaultExpanded = false }) => {
   const [expanded, setExpanded] = React.useState(defaultExpanded)
-
   return (
     <Box sx={{ mb: 2 }}>
       <Box
@@ -51,54 +57,64 @@ const Section: React.FC<SectionProps> = ({ title, children, defaultExpanded = fa
   )
 }
 
+// ------------------------------------------------------------------------------
+// Main OptionsPanel
+// ------------------------------------------------------------------------------
 export const OptionsPanel: React.FC = () => {
-  const { options, setOptions } = useOptionsStore()
+  const {
+    options,
+    setOptions,
+    containers,
+    codecs,
+    compatibility,
+    setContainers,
+    setCodecs,
+    setCompatibility,
+  } = useOptionsStore()
+
   const { hasVideo } = useUploadStore()
   const { formatError, setFormatError } = useValidationStore()
 
-  // Audio-only formats from backend constants (hardcoded for now)
+  // Fetch formats on mount
-  const audioOnlyFormats = ['mp3', 'm4a', 'ogg', 'opus', 'flac', 'wav', 'aac']
-
-  const handleFormatChange = (e: React.ChangeEvent<HTMLInputElement>) => {
-    const newFormat = e.target.value
-    setOptions({ format: newFormat })
-
-    // Validate format
-    if (audioOnlyFormats.includes(newFormat) && hasVideo && !options.drop_video) {
-      setFormatError(
-        `Format '${newFormat}' does not support video streams. Please enable "Drop video" or choose a container that supports video (e.g., MKV, MP4).`
-      )
-    } else {
-      setFormatError(null)
-    }
-  }
-
-  const handleDropVideoChange = (e: React.ChangeEvent<HTMLInputElement>) => {
-    const checked = e.target.checked
-    setOptions({ drop_video: checked })
-    // Re-validate format
-    if (audioOnlyFormats.includes(options.format) && hasVideo && !checked) {
-      setFormatError(
-        `Format '${options.format}' does not support video streams. Please enable "Drop video" or choose a container that supports video (e.g., MKV, MP4).`
-      )
-    } else {
-      setFormatError(null)
-    }
-  }
-
-  // Re-validate when hasVideo changes (e.g., after upload)
   useEffect(() => {
-    const shouldShowError = audioOnlyFormats.includes(options.format) && hasVideo && !options.drop_video
+    const fetchFormats = async () => {
-    const newError = shouldShowError
+      try {
-      ? `Format '${options.format}' does not support video streams. Please enable "Drop video" or choose a container that supports video (e.g., MKV, MP4).`
+        const data = await getFormats()
-      : null
+        setContainers(data.containers || [])
-
+        setCodecs(data.codecs || [])
-    // Only update if the error state actually changes
+        setCompatibility(data.compatibility || {})
-    if (newError !== formatError) {
+      } catch (err) {
-      setFormatError(newError)
+        console.error('Failed to fetch formats:', err)
       }
-  }, [hasVideo, options.format, options.drop_video, formatError, setFormatError])
+    }
+    fetchFormats()
+  }, [setContainers, setCodecs, setCompatibility])
 
+  // --------------------------------------------------------------
+  // Filter codec options based on selected container
+  // --------------------------------------------------------------
+  const { filteredAudioCodecs, filteredVideoCodecs } = useFilterCodecs(compatibility, options.container, codecs)
+
+  // --------------------------------------------------------------
+  // Validate compatibility
+  // --------------------------------------------------------------
+  useFormatValidation(options, hasVideo, compatibility, containers, setFormatError)
+
+  // --------------------------------------------------------------
+  // Handlers
+  // --------------------------------------------------------------
+  const handleChange = (field: keyof SplitOptions, value: any) => {
+    setOptions({ [field]: value })
+  }
+
+  const handleContainerChange = (e: React.ChangeEvent<HTMLInputElement>) => {
+    const value = e.target.value === '' ? null : e.target.value
+    handleChange('container', value)
+  }
+
+  // --------------------------------------------------------------
+  // Render
+  // --------------------------------------------------------------
   return (
     <Paper sx={{ p: 3 }}>
       <Typography variant="h6" sx={{ mb: 2 }}>
@@ -111,60 +127,101 @@ export const OptionsPanel: React.FC = () => {
         </Alert>
       )}
 
-      {/* Output Settings */}
+      {/* ------------------------------------------------------------------------
+          Output Settings
+      ------------------------------------------------------------------------ */}
       <Section title="Output Settings" defaultExpanded>
         <Box sx={{ display: 'flex', flexDirection: 'column', gap: 2 }}>
+          {/* Container dropdown */}
           <TextField
             label="Container"
             select
-            value={options.format}
+            value={options.container ?? ''}
-            onChange={handleFormatChange}
+            onChange={handleContainerChange}
             fullWidth
             size="small"
             error={!!formatError}
             helperText={
-              formatError || "Determines the output file extension and container structure."
+              formatError || "Select a container (auto-detect if empty)."
             }
           >
-            <MenuItem value="mp3">MP3 (.mp3)</MenuItem>
+            <MenuItem value="">Auto-detect</MenuItem>
-            <MenuItem value="m4a">M4A (.m4a)</MenuItem>
+            {containers.map((c) => (
-            <MenuItem value="mkv">MKV (.mkv)</MenuItem>
+              <MenuItem key={c.name} value={c.name}>
-            <MenuItem value="mp4">MP4 (.mp4)</MenuItem>
+                {c.name.toUpperCase()} ({c.extension})
-            <MenuItem value="ogg">OGG (.ogg)</MenuItem>
+              </MenuItem>
-            <MenuItem value="opus">OPUS (.opus)</MenuItem>
+            ))}
-            <MenuItem value="flac">FLAC (.flac)</MenuItem>
-            <MenuItem value="wav">WAV (.wav)</MenuItem>
-            <MenuItem value="aac">AAC (.aac)</MenuItem>
           </TextField>
 
-          {/* Transcode option – remains unchanged but clearly labeled */}
+          {/* Audio Codec dropdown */}
           <TextField
-            label="Audio Codec (Transcode)"
+            label="Audio Codec"
             select
-            value={options.transcode_to || ''}
+            value={options.audio_codec}
-            onChange={(e) => handleChange('transcode_to', e.target.value || undefined)}
+            onChange={(e) => handleChange('audio_codec', e.target.value)}
             fullWidth
             size="small"
-            helperText="Select an audio codec to re-encode, or keep 'Copy' to preserve the original."
+            helperText="Audio codec (copy = keep original)"
           >
-            <MenuItem value="">Copy (no transcoding)</MenuItem>
+            <MenuItem value="copy">Copy (original)</MenuItem>
-            <MenuItem value="libmp3lame">MP3 (LAME)</MenuItem>
+            {filteredAudioCodecs.map((c) => (
-            <MenuItem value="aac">AAC</MenuItem>
+              <MenuItem key={c.name} value={c.name}>
-            <MenuItem value="libopus">OPUS</MenuItem>
+                {c.name.toUpperCase()}
+              </MenuItem>
+            ))}
           </TextField>
 
+          {/* Video Codec dropdown */}
+          <TextField
+            label="Video Codec"
+            select
+            value={options.video_codec}
+            onChange={(e) => handleChange('video_codec', e.target.value)}
+            fullWidth
+            size="small"
+            helperText="Video codec (copy = keep original)"
+            disabled={!hasVideo || options.drop_video}
+          >
+            <MenuItem value="copy">Copy (original)</MenuItem>
+            {filteredVideoCodecs.map((c) => (
+              <MenuItem key={c.name} value={c.name}>
+                {c.name.toUpperCase()}
+              </MenuItem>
+            ))}
+          </TextField>
+
+          {/* Video Quality */}
+          <TextField
+            label="Video Quality"
+            type="number"
+            value={options.video_quality ?? ''}
+            onChange={(e) => {
+              const val = e.target.value === '' ? null : parseInt(e.target.value, 10)
+              handleChange('video_quality', val)
+            }}
+            fullWidth
+            size="small"
+            disabled={!hasVideo || options.drop_video}
+            helperText="Optional quality value (encoder-specific; e.g., 1-31 for libx264, 0-10 for Theora)"
+            InputProps={{
+              inputProps: { min: 0, max: 51, step: 1 },
+            }}
+          />
+
+          {/* Drop video (if video present) */}
           {hasVideo && (
             <FormControlLabel
               control={
                 <Switch
                   checked={options.drop_video}
-                  onChange={handleDropVideoChange}
+                  onChange={(e) => handleChange('drop_video', e.target.checked)}
                 />
               }
               label="Drop video streams"
             />
           )}
 
+          {/* Drop subtitles */}
           <FormControlLabel
             control={
               <Switch
@@ -177,7 +234,9 @@ export const OptionsPanel: React.FC = () => {
         </Box>
       </Section>
 
-      {/* Filename Settings */}
+      {/* ------------------------------------------------------------------------
+          Filename Settings
+      ------------------------------------------------------------------------ */}
       <Section title="Filename Settings">
         <Box sx={{ display: 'flex', flexDirection: 'column', gap: 2 }}>
           <TextField
@@ -233,7 +292,9 @@ export const OptionsPanel: React.FC = () => {
         </Box>
       </Section>
 
-      {/* Metadata Settings */}
+      {/* ------------------------------------------------------------------------
+          Metadata Settings
+      ------------------------------------------------------------------------ */}
       <Section title="Metadata Settings">
         <Box sx={{ display: 'flex', flexDirection: 'column', gap: 2 }}>
           <TextField
@@ -264,7 +325,7 @@ export const OptionsPanel: React.FC = () => {
             type="number"
             value={options.comment_stream ?? ''}
             onChange={(e) =>
-              handleChange('comment_stream', e.target.value === '' ? null : parseInt(e.target.value))
+              handleChange('comment_stream', e.target.value === '' ? null : parseInt(e.target.value, 10))
             }
             size="small"
             disabled={options.no_comment}
@@ -289,7 +350,9 @@ export const OptionsPanel: React.FC = () => {
         </Box>
       </Section>
 
-      {/* Tracklist Settings */}
+      {/* ------------------------------------------------------------------------
+          Tracklist Settings
+      ------------------------------------------------------------------------ */}
       <Section title="Tracklist Settings" defaultExpanded>
         <Box sx={{ display: 'flex', flexDirection: 'column', gap: 2 }}>
           <TextField
@@ -304,9 +367,4 @@ export const OptionsPanel: React.FC = () => {
       </Section>
     </Paper>
   )
-
-  // Helper function for option updates
-  function handleChange(field: string, value: any) {
-    setOptions({ [field]: value })
-  }
 }

web/frontend/src/components/UploadZone.tsx

@@ -7,7 +7,7 @@ import { useOptionsStore } from '../stores/optionsStore'  // NEW
 import { uploadFile, getTaskInfo, getRecommendedFormat } from '../api/client'  // NEW
 import { useTaskStore } from '../stores/taskStore'
 
-const ALLOWED_EXTENSIONS = ['.mp3', '.flac', '.wav', '.m4a', '.ogg', '.opus', '.aac', '.wma', '.aiff', '.alac', '.ac3']
+const ALLOWED_EXTENSIONS = ['.mp3', '.flac', '.wav', '.m4a', '.ogg', '.opus', '.aac', '.wma', '.aiff', '.alac', '.ac3', '.mp4', '.mkv', '.webm']
 
 export const UploadZone: React.FC = () => {
   const {
@@ -70,9 +70,10 @@ export const UploadZone: React.FC = () => {
 
           // Fetch recommended format and update options
           try {
+            // Inside UploadZone.tsx, after fetching recommended format:
             const rec = await getRecommendedFormat(taskId)
-            // Update only the format; keep other options (e.g., transcode_to) as defaults
+            // Update options store with container (not format)
-            setOptions({ format: rec.format })
+            setOptions({ container: rec.format })
           } catch (err) {
             console.warn('Failed to fetch recommended format, using default', err)
           }
@@ -95,7 +96,7 @@ export const UploadZone: React.FC = () => {
   const { getRootProps, getInputProps, isDragActive } = useDropzone({
     onDrop,
     accept: {
-      'audio/*': ALLOWED_EXTENSIONS,
+      'media/*': ALLOWED_EXTENSIONS
     },
     multiple: false,
     disabled: isUploading,

web/frontend/src/hooks/useFilterCodecs.ts

@@ -0,0 +1,31 @@
+import { useMemo } from 'react'
+import { CodecInfo } from '../types'
+
+export interface CompatibilityEntry {
+  audio: string[] | null
+  video: string[] | null
+}
+
+export function useFilterCodecs(
+  compatibility: Record<string, CompatibilityEntry>,
+  container: string | null,
+  codecs: CodecInfo[]
+) {
+  const filteredAudioCodecs = useMemo(() => {
+    const entry = compatibility?.[container || '']
+    if (!entry) return codecs.filter(c => c.codec_type === 'audio')
+    const audioList = entry.audio
+    if (audioList === null) return codecs.filter(c => c.codec_type === 'audio')
+    return codecs.filter(c => c.codec_type === 'audio' && audioList.includes(c.name))
+  }, [compatibility, container, codecs])
+
+  const filteredVideoCodecs = useMemo(() => {
+    const entry = compatibility?.[container || '']
+    if (!entry) return codecs.filter(c => c.codec_type === 'video')
+    const videoList = entry.video
+    if (videoList === null) return codecs.filter(c => c.codec_type === 'video')
+    return codecs.filter(c => c.codec_type === 'video' && videoList.includes(c.name))
+  }, [compatibility, container, codecs])
+
+  return { filteredAudioCodecs, filteredVideoCodecs }
+}

web/frontend/src/hooks/useFormatValidation.ts

@@ -0,0 +1,56 @@
+import { useEffect } from 'react'
+import { ContainerInfo } from '../types'
+import { CompatibilityEntry } from './useFilterCodecs'
+
+export function useFormatValidation(
+  options: {
+    container: string | null
+    audio_codec: string
+    video_codec: string
+    drop_video: boolean
+  },
+  hasVideo: boolean,
+  compatibility: Record<string, CompatibilityEntry>,
+  containers: ContainerInfo[],
+  setFormatError: (error: string | null) => void
+) {
+  useEffect(() => {
+    const selectedContainer = containers.find(c => c.name === options.container)
+    if (!selectedContainer?.supports_video && hasVideo && !options.drop_video) {
+      setFormatError(
+        `Container '${options.container}' does not support video streams. Please enable "Drop video" or choose a container that supports video.`
+      )
+      return
+    }
+
+    // Check audio codec compatibility
+    if (options.audio_codec && options.audio_codec !== 'copy' && options.container) {
+      const entry = compatibility?.[options.container]
+      if (entry) {
+        const audioList = entry.audio
+        if (audioList !== null && !audioList.includes(options.audio_codec)) {
+          setFormatError(
+            `Audio codec '${options.audio_codec}' is not supported by container '${options.container}'.`
+          )
+          return
+        }
+      }
+    }
+
+    // Check video codec compatibility
+    if (options.video_codec && options.video_codec !== 'copy' && options.container && hasVideo && !options.drop_video) {
+      const entry = compatibility?.[options.container]
+      if (entry) {
+        const videoList = entry.video
+        if (videoList !== null && !videoList.includes(options.video_codec)) {
+          setFormatError(
+            `Video codec '${options.video_codec}' is not supported by container '${options.container}'.`
+          )
+          return
+        }
+      }
+    }
+
+    setFormatError(null)
+  }, [options.container, options.audio_codec, options.video_codec, options.drop_video, hasVideo, compatibility, containers, setFormatError])
+}

web/frontend/src/stores/optionsStore.ts

@@ -1,6 +1,5 @@
-// web/frontend/src/stores/optionsStore.ts
 import { create } from 'zustand'
-import { SplitOptions } from '../types'
+import { SplitOptions, ContainerInfo, CodecInfo } from '../types'
 import {
   DEFAULT_FORMAT,
   DEFAULT_OUTPUT_TEMPLATE,
@@ -17,13 +16,16 @@ import {
   DEFAULT_NUMBER_TRACKS,
   DEFAULT_REPLACE_BAD_CHARS,
   DEFAULT_SKIP_EXISTING,
-  DEFAULT_TRANSCODE_TO,
   DEFAULT_TRACKLIST_FORMAT,
 } from '../constants/generated'
 
+// We use DEFAULT_FORMAT only as a fallback; container default is null (auto-detect)
 const DEFAULT_OPTIONS: SplitOptions = {
-  format: DEFAULT_FORMAT,
+  container: null,
-  transcode_to: DEFAULT_TRANSCODE_TO ?? '',
+  audio_codec: 'copy',
+  video_codec: 'copy',
+  subtitle_codec: 'copy',
+  video_quality: null,
   drop_video: DEFAULT_DROP_VIDEO,
   drop_subs: DEFAULT_DROP_SUBS,
   number_tracks: DEFAULT_NUMBER_TRACKS,
@@ -43,15 +45,33 @@ const DEFAULT_OPTIONS: SplitOptions = {
 
 interface OptionsState {
   options: SplitOptions
-  setOptions: (options: Partial<SplitOptions>) => void
+  containers: ContainerInfo[]
+  codecs: CodecInfo[]
+  compatibility: Record<string, { audio: string[] | null; video: string[] | null }>
+  setOptions: (newOptions: Partial<SplitOptions>) => void
+  setContainers: (containers: ContainerInfo[]) => void
+  setCodecs: (codecs: CodecInfo[]) => void
+  setCompatibility: (compat: Record<string, { audio: string[] | null; video: string[] | null }>) => void
   reset: () => void
 }
 
 export const useOptionsStore = create<OptionsState>((set) => ({
   options: { ...DEFAULT_OPTIONS },
+  containers: [],
+  codecs: [],
+  compatibility: {},
   setOptions: (newOptions) =>
     set((state) => ({
       options: { ...state.options, ...newOptions },
     })),
-  reset: () => set({ options: { ...DEFAULT_OPTIONS } }),
+  setContainers: (containers) => set({ containers }),
+  setCodecs: (codecs) => set({ codecs }),
+  setCompatibility: (compatibility) => set({ compatibility }),
+  reset: () =>
+    set({
+      options: { ...DEFAULT_OPTIONS },
+      containers: [],
+      codecs: [],
+      compatibility: {},
+    }),
 }))

web/frontend/src/types/index.ts

@@ -22,8 +22,11 @@ export interface TaskStatus {
 }
 
 export interface SplitOptions {
-  format: string
+  container: string | null          // null = auto-detect
-  transcode_to?: string
+  audio_codec: string               // 'copy' or encoder name
+  video_codec: string               // 'copy' or encoder name
+  subtitle_codec: string            // 'copy' or encoder name
+  video_quality: number | null      // encoder-specific integer
   drop_video: boolean
   drop_subs: boolean
   number_tracks: boolean
@@ -38,7 +41,34 @@ export interface SplitOptions {
   comment_stream: number | null
   merge_comments: boolean
   comment_separator: string
-  tracklist_format: string
+  tracklist_format: string          // for frontend parsing
+}
+
+export interface ContainerInfo {
+  name: string
+  ffmpeg: string
+  extension: string
+  supports_video: boolean
+  supports_subs: boolean
+}
+
+export interface CodecInfo {
+  name: string
+  ffmpeg: string
+  recommended_container: string
+  recommended_extension: string
+  codec_type: 'audio' | 'video' | 'subtitle'
+}
+
+export interface CompatibilityEntry {
+  audio: string[] | null
+  video: string[] | null
+}
+
+export interface FormatsResponse {
+  containers: ContainerInfo[]
+  codecs: CodecInfo[]
+  compatibility: Record<string, CompatibilityEntry>
 }
 
 export interface UploadResponse {