Determine merge container better (See desc) (#1482)

* Determine the container early. Closes #4069
* Use codecs instead of just file extensions
* Obey `--prefer-free-formats`
* Allow fallbacks in `--merge-output`

Authored by: pukkandan, selfisekai

README.md

@@ -858,10 +858,10 @@ ## Video Format Options:
                                     downloadable
     -F, --list-formats              List available formats of each video.
                                     Simulate unless --no-simulate is used
-    --merge-output-format FORMAT    Container to use when merging formats (e.g.
-                                    bestvideo+bestaudio). Ignored if no merge is
-                                    required. (currently supported: avi, flv,
-                                    mkv, mov, mp4, webm)
+    --merge-output-format FORMAT    Containers that may be used when merging
+                                    formats, separated by "/" (Eg: "mp4/mkv").
+                                    Ignored if no merge is required. (currently
+                                    supported: avi, flv, mkv, mov, mp4, webm)
 
 ## Subtitle Options:
     --write-subs                    Write subtitle file

test/test_utils.py

@@ -53,6 +53,7 @@
     fix_xml_ampersands,
     float_or_none,
     format_bytes,
+    get_compatible_ext,
     get_element_by_attribute,
     get_element_by_class,
     get_element_html_by_attribute,
@@ -1843,6 +1844,31 @@ def test_determine_file_encoding(self):
         self.assertEqual(determine_file_encoding('# coding: utf-32-be'.encode('utf-32-be')), ('utf-32-be', 0))
         self.assertEqual(determine_file_encoding('# coding: utf-16-le'.encode('utf-16-le')), ('utf-16-le', 0))
 
+    def test_get_compatible_ext(self):
+        self.assertEqual(get_compatible_ext(
+            vcodecs=[None], acodecs=[None, None], vexts=['mp4'], aexts=['m4a', 'm4a']), 'mkv')
+        self.assertEqual(get_compatible_ext(
+            vcodecs=[None], acodecs=[None], vexts=['flv'], aexts=['flv']), 'flv')
+
+        self.assertEqual(get_compatible_ext(
+            vcodecs=[None], acodecs=[None], vexts=['mp4'], aexts=['m4a']), 'mp4')
+        self.assertEqual(get_compatible_ext(
+            vcodecs=[None], acodecs=[None], vexts=['mp4'], aexts=['webm']), 'mkv')
+        self.assertEqual(get_compatible_ext(
+            vcodecs=[None], acodecs=[None], vexts=['webm'], aexts=['m4a']), 'mkv')
+        self.assertEqual(get_compatible_ext(
+            vcodecs=[None], acodecs=[None], vexts=['webm'], aexts=['webm']), 'webm')
+
+        self.assertEqual(get_compatible_ext(
+            vcodecs=['h264'], acodecs=['mp4a'], vexts=['mov'], aexts=['m4a']), 'mp4')
+        self.assertEqual(get_compatible_ext(
+            vcodecs=['av01.0.12M.08'], acodecs=['opus'], vexts=['mp4'], aexts=['webm']), 'webm')
+
+        self.assertEqual(get_compatible_ext(
+            vcodecs=['vp9'], acodecs=['opus'], vexts=['webm'], aexts=['webm'], preferences=['flv', 'mp4']), 'mp4')
+        self.assertEqual(get_compatible_ext(
+            vcodecs=['av1'], acodecs=['mp4a'], vexts=['webm'], aexts=['m4a'], preferences=('webm', 'mkv')), 'mkv')
+
 
 if __name__ == '__main__':
     unittest.main()

yt_dlp/YoutubeDL.py

@@ -102,6 +102,7 @@
     format_decimal_suffix,
     format_field,
     formatSeconds,
+    get_compatible_ext,
     get_domain,
     int_or_none,
     iri_to_uri,
@@ -134,6 +135,7 @@
     timetuple_from_msec,
     to_high_limit_path,
     traverse_obj,
+    try_call,
     try_get,
     url_basename,
     variadic,
@@ -372,7 +374,7 @@ class YoutubeDL:
 
                        Progress hooks are guaranteed to be called at least twice
                        (with status "started" and "finished") if the processing is successful.
-    merge_output_format: Extension to use when merging formats.
+    merge_output_format: "/" separated list of extensions to use when merging formats.
     final_ext:         Expected final extension; used to detect when the file was
                        already downloaded and converted
     fixup:             Automatically correct known faults of the file.
@@ -2088,14 +2090,13 @@ def _merge(formats_pair):
             the_only_video = video_fmts[0] if len(video_fmts) == 1 else None
             the_only_audio = audio_fmts[0] if len(audio_fmts) == 1 else None
 
-            output_ext = self.params.get('merge_output_format')
-            if not output_ext:
-                if the_only_video:
-                    output_ext = the_only_video['ext']
-                elif the_only_audio and not video_fmts:
-                    output_ext = the_only_audio['ext']
-                else:
-                    output_ext = 'mkv'
+            output_ext = get_compatible_ext(
+                vcodecs=[f.get('vcodec') for f in video_fmts],
+                acodecs=[f.get('acodec') for f in audio_fmts],
+                vexts=[f['ext'] for f in video_fmts],
+                aexts=[f['ext'] for f in audio_fmts],
+                preferences=(try_call(lambda: self.params['merge_output_format'].split('/'))
+                             or self.params.get('prefer_free_formats') and ('webm', 'mkv')))
 
             filtered = lambda *keys: filter(None, (traverse_obj(fmt, *keys) for fmt in formats_info))
 
@@ -3067,33 +3068,9 @@ def existing_video_file(*filepaths):
                         return
 
                 if info_dict.get('requested_formats') is not None:
-
-                    def compatible_formats(formats):
-                        # TODO: some formats actually allow this (mkv, webm, ogg, mp4), but not all of them.
-                        video_formats = [format for format in formats if format.get('vcodec') != 'none']
-                        audio_formats = [format for format in formats if format.get('acodec') != 'none']
-                        if len(video_formats) > 2 or len(audio_formats) > 2:
-                            return False
-
-                        # Check extension
-                        exts = {format.get('ext') for format in formats}
-                        COMPATIBLE_EXTS = (
-                            {'mp3', 'mp4', 'm4a', 'm4p', 'm4b', 'm4r', 'm4v', 'ismv', 'isma'},
-                            {'webm'},
-                        )
-                        for ext_sets in COMPATIBLE_EXTS:
-                            if ext_sets.issuperset(exts):
-                                return True
-                        # TODO: Check acodec/vcodec
-                        return False
-
                     requested_formats = info_dict['requested_formats']
                     old_ext = info_dict['ext']
                     if self.params.get('merge_output_format') is None:
-                        if not compatible_formats(requested_formats):
-                            info_dict['ext'] = 'mkv'
-                            self.report_warning(
-                                'Requested formats are incompatible for merge and will be merged into mkv')
                         if (info_dict['ext'] == 'webm'
                                 and info_dict.get('thumbnails')
                                 # check with type instead of pp_key, __name__, or isinstance

yt_dlp/__init__.py

@@ -228,7 +228,8 @@ def validate_minmax(min_val, max_val, min_name, max_name=None):
         validate_regex('format sorting', f, InfoExtractor.FormatSort.regex)
 
     # Postprocessor formats
-    validate_in('merge output format', opts.merge_output_format, FFmpegMergerPP.SUPPORTED_EXTS)
+    validate_regex('merge output format', opts.merge_output_format,
+                   r'({0})(/({0}))*'.format('|'.join(map(re.escape, FFmpegMergerPP.SUPPORTED_EXTS))))
     validate_regex('audio format', opts.audioformat, FFmpegExtractAudioPP.FORMAT_RE)
     validate_in('subtitle format', opts.convertsubtitles, FFmpegSubtitlesConvertorPP.SUPPORTED_EXTS)
     validate_regex('thumbnail format', opts.convertthumbnails, FFmpegThumbnailsConvertorPP.FORMAT_RE)

yt_dlp/options.py

@@ -782,7 +782,8 @@ def _alias_callback(option, opt_str, value, parser, opts, nargs):
         '--merge-output-format',
         action='store', dest='merge_output_format', metavar='FORMAT', default=None,
         help=(
-            'Container to use when merging formats (e.g. bestvideo+bestaudio). Ignored if no merge is required. '
+            'Containers that may be used when merging formats, separated by "/" (Eg: "mp4/mkv"). '
+            'Ignored if no merge is required. '
             f'(currently supported: {", ".join(sorted(FFmpegMergerPP.SUPPORTED_EXTS))})'))
     video_format.add_option(
         '--allow-unplayable-formats',

yt_dlp/utils.py

@@ -3456,6 +3456,46 @@ def parse_codecs(codecs_str):
     return {}
 
 
+def get_compatible_ext(*, vcodecs, acodecs, vexts, aexts, preferences=None):
+    assert len(vcodecs) == len(vexts) and len(acodecs) == len(aexts)
+
+    allow_mkv = not preferences or 'mkv' in preferences
+
+    if allow_mkv and max(len(acodecs), len(vcodecs)) > 1:
+        return 'mkv'  # TODO: any other format allows this?
+
+    # TODO: All codecs supported by parse_codecs isn't handled here
+    COMPATIBLE_CODECS = {
+        'mp4': {
+            'av1', 'hevc', 'avc1', 'mp4a',  # fourcc (m3u8, mpd)
+            'h264', 'aacl',  # Set in ISM
+        },
+        'webm': {
+            'av1', 'vp9', 'vp8', 'opus', 'vrbs',
+            'vp9x', 'vp8x',  # in the webm spec
+        },
+    }
+
+    sanitize_codec = functools.partial(try_get, getter=lambda x: x.split('.')[0].replace('0', ''))
+    vcodec, acodec = sanitize_codec(vcodecs[0]), sanitize_codec(acodecs[0])
+
+    for ext in preferences or COMPATIBLE_CODECS.keys():
+        codec_set = COMPATIBLE_CODECS.get(ext, set())
+        if ext == 'mkv' or codec_set.issuperset((vcodec, acodec)):
+            return ext
+
+    COMPATIBLE_EXTS = (
+        {'mp3', 'mp4', 'm4a', 'm4p', 'm4b', 'm4r', 'm4v', 'ismv', 'isma', 'mov'},
+        {'webm'},
+    )
+    for ext in preferences or vexts:
+        current_exts = {ext, *vexts, *aexts}
+        if ext == 'mkv' or current_exts == {ext} or any(
+                ext_sets.issuperset(current_exts) for ext_sets in COMPATIBLE_EXTS):
+            return ext
+    return 'mkv' if allow_mkv else preferences[-1]
+
+
 def urlhandle_detect_ext(url_handle):
     getheader = url_handle.headers.get