[FFmpeg-devel] Late SEI is not implemented (providing a sample)

[FFmpeg-devel] Late SEI is not implemented (providing a sample)

[Miguel Borges de Freitas]

Dear all,

While updating Kodi to use the ffmpeg provided A53 side data for
closed captions instead of our custom (old) demuxer (c.f.
https://github.com/xbmc/xbmc/pull/22333) and running it against a
battery of test samples I've found the following messages in the log
for one particular sample:

[ffmpeg/video] h264: Late SEI is not implemented. Update your FFmpeg
version to the newest one from Git. If the problem still occurs, it
means that your file has a feature which has not been implemented.
[ffmpeg/video] h264: If you want to help, upload a sample of this file
to https://streams.videolan.org/upload/ and contact the ffmpeg-devel
mailing list. (ffmpeg-devel@ffmpeg.org)

This happens with ffmpeg version 5.1.2 and current master.
To reproduce the problem you can simply open it with ffplay:

ffplay https://livesim.dashif.org/dash/vod/testpic_2s/cea608.mpd

The sample in question has two closed caption streams, although in
ffmpeg none is detected/demuxed (a53 side data is empty). You can
validate the proper behavior using dash.js for example:

https://players.akamai.com/players/dashjs?streamUrl=https%3A%2F%2Flivesim.dashif.org%2Fdash%2Fvod%2Ftestpic_2s%2Fcea608.mpd

Hope you find this helpful,

Best regards,

Miguel
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Re: [FFmpeg-devel] Late SEI is not implemented (providing a sample)

[Miguel Borges de Freitas]

Answering my own question here in case someone else stumbles into this, it turns out those streams were completely broken:

- The CC data SEI NAL units were defined after the primary coded picture which violates the H264 standard
- The user data part of SEI was lacking the marker_bits (0xFF) at the end

Both issues were fixed upstream by the Dash industry forum and the public samples regenerated after the report, they work correctly now in ffmpeg.
Cross-reference: https://github.com/Dash-Industry-Forum/dash-live-source-simulator/issues/115

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