Initial commit. Basic featues are implemented

formats.py

@@ -0,0 +1,55 @@
+"""Container format decision and validation."""
+
+from .constants import FORMAT_INFO
+
+
+def determine_output_format(stream_info, user_format, transcode_audio):
+    """
+    Decide which container format to use.
+
+    Args:
+        stream_info: Dict from get_stream_info().
+        user_format: User‑requested format (or None).
+        transcode_audio: Audio codec to transcode to (or None).
+
+    Returns:
+        A format name that exists in FORMAT_INFO.
+    """
+    if user_format:
+        return user_format
+
+    # If video or subtitles exist, use MKV (which supports everything).
+    if stream_info['has_video'] or stream_info['has_subtitle']:
+        return 'matroska'
+
+    # Audio‑only: choose based on the current audio codec.
+    audio_codec = stream_info.get('audio_codec', '')
+    if audio_codec == 'mp3':
+        return 'mp3'
+    else:
+        return 'mp4'  # .m4a
+
+
+def validate_format_compatibility(format_name, stream_info, drop_video, drop_subs):
+    """
+    Ensure the chosen container can accommodate the streams we intend to keep.
+
+    Raises:
+        ValueError: If the format is incompatible with the intended streams.
+    """
+    info = FORMAT_INFO.get(format_name)
+    if not info:
+        print(f"Warning: Unknown format '{format_name}'. Proceeding, but may fail.")
+        return
+
+    if info['audio_only']:
+        if stream_info['has_video'] and not drop_video:
+            raise ValueError(
+                f"Format '{format_name}' does not support video streams. "
+                "Please use --drop-video or choose a container that supports video."
+            )
+        if stream_info['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."
+            )