Audio is dropped when bitstreaming ATMOS on some movies

[danbezerra]

Important Information

Provide following Information:

• mpv version: mpv 0.34.0-116-gd92cf77be5
• Windows Version : 10.0.19043 Build 19043
• Source of the mpv binary: https://sourceforge.net/projects/mpv-player-windows/files/
• If known which version of mpv introduced the problem: N/A

Reproduction steps

1. Choose a video file with Atmos enabled track. For example, a 1:1 rip of Thor Ragnarok UHD Disk with Atmos track.
2. Use a receiver that supports Dolby Atmos - mine is a Denon x3200
3. Make sure that audio-spdif is defined as following: audio-spdif=ac3,dts,dts-hd,eac3,truehd in the config file
4. Play the MKV sample file shared below.

Wait for the audio to drop. The log file will have the following message:
[ 270.588][w][ffmpeg] spdif: Unusual frame timing: 34080 => 35807, 40 samples/frame 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.

Note: This is NOT happening with every Atmos track. So far I noticed it with Spiderman Homecoming and Thor Ragnarok.

Expected behavior

No audio issues. The same MKV works perfectly on MPC-HC with the latest LAV filters (0.75.1).

Log file

https://0x0.st/osB2.txt

Sample files

https://0x0.st/osB6.mkv
(1 minute sample from the movie, including the frame where the audio drop happens)

[LaserEyess]

That line in the log is pretty unambiguous, this is an ffmpeg bug/unimplemented feature. Can you do what it suggests and compile mpv against ffmpeg git master?

[LaserEyess]

That's great but mpv doesn't use LAV filter.

[danbezerra]

Not that it matters for MPV, but Nev just released another version of LAV filters with extra protection/fixes against ATMOS drop outs. Not sure how to get this issue addressed on the MPV/FFMPEG side. I have a sample shared in the original post though.

[LaserEyess]

If it's an issue with an audio codec, it's an ffmpeg issue. From the OP:

[ 270.588][w][ffmpeg] spdif: Unusual frame timing: 34080 => 35807, 40 samples/frame 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.

So, if you're looking to get this fixed, you must report it there. It couldn't be more explicit.

[mitzsch]

It´s already opened on the FFmpeg bug reporter site. Hopefully, someone is able to fix this! (also present on Linux)
https://trac.ffmpeg.org/ticket/9569

[acedogblast]

@mitzsch I have a hacky fix posted on the ffmpeg bug tracker.

[JJenkx]

I vibe coded a portable mpv for windows and linux that includes a linked patched ffmpeg atmos fix https://github.com/JJenkx/mpv-atmos-patched

Edit: I switched the Atmos patch over to these merge requests https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/23542/commits from Nathan Lucas and it is working great. Claude Fable 5 said it was better than the Kodi MAT packer version I had

[nathanlucas]

A potential fix for these issues has an open PR at:
https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/23542

Related changes to mpv to avoid spdifenc/truehd issues when seeking is open at:
#18241

The ffmpeg fix addresses the previously unhandled IEC 61937/MAT frame timing at bluray seamless branches. I have been using these or similar changes for the past month with good results in Windows with my Yamaha RX-A4A and I have also tested on a Samsung S95F TV with mpv in linux. Movies with reproducible audio dropouts at bluray branches, like the Martian (Extended Edition), play through with no drops with these changes.

@mitzsch has a windows build for testing that can be found in the AVSForum mpv thread:
https://www.avsforum.com/posts/64696673/ (check for newer builds in the thread)

[danbezerra]

I tested this implementation provided by Nathan and I can confirm it solves all audio issues I had with Atmos Audio drops before. Challenging titles like Martian extended edition, Dead Men Chest, GoG2, Megan 2.0 extended, etc. All working perfectly with this new fix.

[netExtra]

I tested this implementation provided by Nathan and I can confirm it solves all audio issues I had with Atmos Audio drops before. Challenging titles like Martian extended edition, Dead Men Chest, GoG2, Megan 2.0 extended, etc. All working perfectly with this new fix.

It's not new. Just to you.

[kasper93]

Fixed by: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/23542