-10 seconds audio delay on some FranceTV videos with yt-dlp

Important Information

Information:

• mpv version : 0.34.0
• Debian GNU/Linux Buster (10.11)
• Source of the mpv binary : own compilation (backport) from Debian/unstable package source
• which version of mpv introduced the problem: before 0.33.0 (may possibly be related to changes in yt-dlp)
• yt-dlp version : a109acbf8 (last commit from master on 2021-11-08 (includes tag/version 2021.10.22))
• youtube-dl was not used

Reproduction steps

• Go to https://www.france.tv/france-5/vu/
• Take any recent video (now I use https://www.france.tv/france-5/vu/2916059-emission-du-lundi-8-novembre-2021.html)
• launch with URL like: mpv --no-config 'https://www.france.tv/france-5/vu/2916059-emission-du-lundi-8-novembre-2021.html'

Note: many other (but not all) videos on france.tv can be used to reproduce the problem.

Expected behavior

The video & audio plays smoothly, in sync, and the video plays to the end.

Actual behavior

• The video appears, but the sound is exactly 10 seconds in advance compared to the images.
• Also, when the playback actually starts, the OSD indicates that we are at 00:00:10

It looks like the chunk(s) for the first 10 seconds of sound is simply missing, and that creates the desync. It is possible to compensate with manually adjusting A-V delay, but that then creates glitches sometimes when seeking (and still, the first 10 seconds are missing).

Additional comment about yt-dlp

When downloading the video file with yt-dlp, and then playing the resulting local file with mpv, everything works smoothly.

In other words, doing this works as expected:

• yt-dlp 'https://www.france.tv/france-5/vu/2916059-emission-du-lundi-8-novembre-2021.html'
• mpv "VU - Emission du lundi 8 novembre 2021 [65f29c10-db4a-4c9b-9819-a8eea7bc7588].mp4"

Log file

Here is the log file (gzip compressed): francetv-yt-dlp-bug.txt.gz

Here is an interesting extract, just before the first  [statusline] is shown:

[cplayer] first video frame after restart shown
[osc] osc_init 
[cplayer] audio ready
[cplayer] starting video playback
[cplayer] starting audio playback
[vo/gpu/x11] Disabling screensaver.
[cplayer] playback restart complete @ 10.000000, audio=playing, video=playing
[ao/pulse] starting AO
[vd] Allocating new DR image...
[statusline] AV: 00:00:10 / 00:06:11 (3%) A-V: -0.000 Cache: 1.6s/348KB

Start by reproducing the FranceTV URL with mpv --no-config and inspect the linked compressed log, especially the playback restart at 10 seconds. Compare direct playback with the yt-dlp-downloaded local file. Done means the stream starts at 00:00:00 with audio and video synchronized, plays to the end, and does not lose the initial audio.