Subtitle extraction from streaming media manifests #247

Authored by fstirlitz
Modified from: https://github.com/ytdl-org/youtube-dl/pull/6144

Closes: #73
Fixes:
https://github.com/ytdl-org/youtube-dl/issues/6106
https://github.com/ytdl-org/youtube-dl/issues/14977
https://github.com/ytdl-org/youtube-dl/issues/21438
https://github.com/ytdl-org/youtube-dl/issues/23609
https://github.com/ytdl-org/youtube-dl/issues/28132

Might also fix (untested):
https://github.com/ytdl-org/youtube-dl/issues/15424
https://github.com/ytdl-org/youtube-dl/issues/18267
https://github.com/ytdl-org/youtube-dl/issues/23899
https://github.com/ytdl-org/youtube-dl/issues/24375
https://github.com/ytdl-org/youtube-dl/issues/24595
https://github.com/ytdl-org/youtube-dl/issues/27899

Related:
https://github.com/ytdl-org/youtube-dl/issues/22379
https://github.com/ytdl-org/youtube-dl/pull/24517
https://github.com/ytdl-org/youtube-dl/pull/24886
https://github.com/ytdl-org/youtube-dl/pull/27215

Notes:
* The functions `extractor.common._extract_..._formats` are still kept for compatibility
* Only some extractors have currently been moved to using `_extract_..._formats_and_subtitles`
* Direct subtitle manifests (without a master) are not supported and are wrongly identified as containing video formats
* AES support is untested
* The fragmented TTML subtitles extracted from DASH/ISM are valid, but are unsupported by `ffmpeg` and most video players
    * Their XML fragments can be dumped using `ffmpeg -i in.mp4 -f data -map 0 -c copy out.ttml`.
        Once the unnecessary headers are stripped out of this, it becomes a valid self-contained ttml file
    * The ttml subs downloaded from DASH manifests can also be directly opened with <https://github.com/SubtitleEdit>
* Fragmented WebVTT files extracted from DASH/ISM are also unsupported by most tools
    * Unlike the ttml files, the XML fragments of these cannot be dumped using `ffmpeg`
    * The webtt subs extracted from DASH can be parsed by <https://github.com/gpac/gpac>
    * But validity of the those extracted from ISM are untested

1 files changed, 6 insertions, 1 deletions

diff --git a/yt_dlp/downloader/fragment.py b/yt_dlp/downloader/fragment.py
index a0c1d13ac..fadd0dfc5 100644
--- a/yt_dlp/downloader/fragment.py
+++ b/yt_dlp/downloader/fragment.py
@@ -77,7 +77,10 @@ class FragmentFD(FileDownloader):
         assert 'ytdl_corrupt' not in ctx
         stream, _ = sanitize_open(self.ytdl_filename(ctx['filename']), 'r')
         try:
-            ctx['fragment_index'] = json.loads(stream.read())['downloader']['current_fragment']['index']
+            ytdl_data = json.loads(stream.read())
+            ctx['fragment_index'] = ytdl_data['downloader']['current_fragment']['index']
+            if 'extra_state' in ytdl_data['downloader']:
+                ctx['extra_state'] = ytdl_data['downloader']['extra_state']
         except Exception:
             ctx['ytdl_corrupt'] = True
         finally:
@@ -90,6 +93,8 @@ class FragmentFD(FileDownloader):
                 'index': ctx['fragment_index'],
             },
         }
+        if 'extra_state' in ctx:
+            downloader['extra_state'] = ctx['extra_state']
         if ctx.get('fragment_count') is not None:
             downloader['fragment_count'] = ctx['fragment_count']
         frag_index_stream.write(json.dumps({'downloader': downloader}))