DiscardPadding in Matroska had glitched playback

[fenlaz]

Summary of the bug: Popping / Cracking sound on videos with .MKV format played on MPV and other video players.

How to reproduce: Playing .MKV format videos on MPV. Here is a sample that I have uploaded on my Google Drive: ​https://drive.google.com/drive/folders/1S108QeTOSg1ieo7uFyoqWIYjvPIgNIeO?usp=sharing

Here is a discussion that I have on MPV github page. The devs pointed that this is an FFMPEG issue. ​https://github.com/mpv-player/mpv/issues/15775

I am not good with computers, so I am just merely reporting this bug.

[MasterQuestionable]

͏    Direct link:
͏    ​https://drive.usercontent.google.com/download?confirm=t&export=download&id=1MJQyr0yAnjil2TZzzzyR4sB1zGoUBBau
͏    (~ 774.43 KiB; "Clipped video.mkv")
͏    ​https://drive.usercontent.google.com/download?confirm=t&export=download&id=1kXrCaKq8uNxj7h7fG_LM0shpYnZUeP-N
͏    (~ 919.3 MiB; "Shangri-La Frontier - 20 [BD 1080p x265 OPUS][DUAL][Anipakku].mkv")

͏    Pin-point comments:
͏    ​https://github.com/mpv-player/mpv/issues/15775#issuecomment-2625226381
͏    ​https://github.com/mpv-player/mpv/issues/15775#issuecomment-2624878758

͏    Summary:
͏    Glitched only in Matroska but not otherwise. (raw Opus, MP4 etc.)
͏    [ ^ Also reported bad for CAF. But unsure what's happening. ]

[mkver]

The Opus track contains lots of DiscardPadding elements in the middle of the stream:

mkvinfo -a "/tmp/Shangri-La Frontier - 20 [BD 1080p x265 OPUS][DUAL][Anipakku].mkv" | grep -B 3 -A 1 'Discard padding'

| + Block group
|  + Block: track number 2, 1 frame(s), timestamp 00:00:03.000000000
|   + Frame with size 691
|  + Discard padding: 666666
|  + Block duration: 00:00:00.019000000
--
| + Block group
|  + Block: track number 2, 1 frame(s), timestamp 00:00:05.020000000
|   + Frame with size 522
|  + Discard padding: 333334
|  + Block duration: 00:00:00.020000000
--
| + Block group
|  + Block: track number 2, 1 frame(s), timestamp 00:00:08.040000000
|   + Frame with size 432
|  + Discard padding: 666666
|  + Block duration: 00:00:00.019000000
--
| + Block group
|  + Block: track number 2, 1 frame(s), timestamp 00:00:13.060000000
|   + Frame with size 442
|  + Discard padding: 333333
|  + Block duration: 00:00:00.020000000
...

In a normal file, only the last Block contains a DiscardPadding element. There probably is a bug in the tools/the workflow used to create this file, but that can't be investigated with only the output file and would be a different bug anyway. So I am closing this as invalid.

[MasterQuestionable]

͏    What's the purpose of "DiscardPadding" after all..?
͏    Is the input file precisely broken/invalid?

​https://www.matroska.org/technical/elements.html#DiscardPadding
͏    "The duration of DiscardPadding is not calculated in the duration of the TrackEntry and **SHOULD** be discarded during playback."