Audio dropouts with Dolby Atmos tracks when seeks or chapter skips are used

[Vern Dias]

I believe this may be a possible regression as a similar issues was reported (and fixed) several years ago.

It's a little different, because this case only occurs when a chapter seek or a skip is used during playback.

The end result is the same with the following message being logged:

[ffmpeg] spdif: Unusual frame timing: 21840 => 31612, 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.
[ 70.863][w][ffmpeg] spdif: 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)
[

Unfortunately the occurrence of the audio skips appears to be random, so it would be almost impossible to provide a file.

ENVIRONMENT:

mpv 0.35.0-513-gfc3e28f1 Copyright © 2000-2023 mpv/MPlayer/mplayer2 projects
built on Sun Jul 09 12:29:05 2023
libplacebo version: v6.292.0-1-gb959cab-dirty
FFmpeg version: N-111383-g20b868809
FFmpeg library versions:
libavutil 58.14.100
libavcodec 60.22.100
libavformat 60.10.100
libswscale 7.3.100
libavfilter 9.8.102
libswresample 4.11.100

Audio is being bit streamed via HDMI

DESCRIPTION OF THE ISSUE:

When playing a BD or UHD disc with a Dolby ATMOS audio track selected and using bit-streaming, any seeks or chapter skips will cause intermittent audio dropouts. These usually do not occur immediately after the chapter skip or seek, but begin several minutes later and with varying frequency.

Playing the same disk without any seeks or chapter skips does not show this issue. I also don't believe that this occurs when bit-streaming is disabled.

The movie used for the attached log files was "Mamma Mia, Here We Go Again" (UHD 4K), although I have seen the same issues occur on a number of different Dolby ATMOS titles, but only after I have performed a chapter skip or timed seek.

Expected behavior: Normal playback

Actual behavior: Intermittent audio dropouts when bit-streaming Dolby ATMOS tracks.
I have attached two log files

Atmos_no_audio_drops_with_no_seeks_chapters.txt

was created by doing a complete showing of the movie with no user intervention.

Atmos_audio_drops_seeks_chapters.txt

was created by starting the movie, then performing several chapter skips and also several timed seeks just after starting playback. Playback was ended after a few occurrences of the audio dropouts.

One other oddity I see is that the refresh rate which should be 23.976 is incorrect starting here in the TrueHD_audio_drop_seeks_chapters.txt log file:
71.253][v][vo/gpu-next/libplacebo] Estimated source FPS: 23.953, display FPS: 23.953

I wonder if this may be the actual cause of the audio dropouts.

[Vern Dias]

Failure Scenario

[Vern Dias]

Normal operation (No user intervention, no chapter skips or seeks)

[Balling]

Dup of #9569?

Estimated source FPS: 23.953, display FPS: 23.953

Update mpv. This is a bug, that was fixed when I complained about it.

[Vern Dias]

Apparently not fixed, at least in the scenario I have described.

Also referenced here:
​https://patchwork.ffmpeg.org/project/ffmpeg/patch/20200412195626.9090-1-anssi.hannula@iki.fi/

When will we see a final fix that also covers the seek / chapter skip scenario merged into the released code that others like MPV are using?

Until then, Directshow remains the only viable solution for playing these titles.

[Vern Dias]

* Update mpv. This is a bug, that was fixed when I complained about it.

Running the latest daily build of MPV. Nothing to update.

[danbez]

This one is a less impactful variation of #9569 as it is only present when you skip forward/backwards a video with Atmos audio track. I also confirm this is still present with the latest MPV build from Shinchiro (20230712).

[Vern Dias]

FWIW, in the process of troubleshooting this issue, I used a different media player (Zoom Player + MadVR), which had been dropout free on Atmos up to to now.

Surprise, the dropouts were now present on this player as well.

The only recent change was updating LAV Filters to 77.1. Reverting to 76.1 solved the issue on this player. To me this points to an issue with the LAV Filter code.

[Balling]

Until then, Directshow remains the only viable solution for playing these titles.

What?? You mean Lavfilters.

I am talking about wrong fps of display that corrupts the video fps.

FPS: 23.953, display FPS: 23.953

That IS a bug.

[Balling]

Also referenced here:

​​https://patchwork.ffmpeg.org/project/ffmpeg/patch/20200412195626.9090-1-anssi.hannula@iki.fi/

That patch is unrelated really. It is a fix for specific sample. This one sample: ​https://web.archive.org/web/20210419182732/https://files.1f0.de/samples/incredibles2-truehd-bitstreaming.thd

[Balling]

This one is a less impactful variation of #9569 as it is only present when you skip forward/backwards a video

That bug also happens because of seek.

[danbez]

Replying to Balling:

This one is a less impactful variation of #9569 as it is only present when you skip forward/backwards a video

That bug also happens because of seek.

#9569 could also be triggered by seamless branching as described in the original post. I actually provided a sample using a 1:1 rip of Blue Brothers 4K UHD where the sound would always disappear in the same spot (branching). But this part seems to be resolved, leaving us with only but still annoying skip forward/backwards issue.

[Vern Dias]

"But this part seems to be resolved, leaving us with only but still annoying skip forward/backwards issue."

This is, unfortunately, not actually true.

Further testing has shown me that it's also showing up in normal playback as well.

It's present both on MPV and also on multiple Directshow players using LAVFilters 77.x and is not dependent on using chapter seeks or skips.

'Significantly, reverting to LAVFilters to 76.1 results in dropouts no longer occurring using Directshow based players, even with chapter skips or seeks.

However, when not doing any chapter skips or seeks symptoms are different in that the dropouts are less frequent, but longer.

Since they are random and not repeatable, this indicates the issue is not related to seamless branching.

I understand that there is a fix coming for JRiver for this issue, hopefully that will also fix the issues on other platforms.