[3.0.11] One second silence of mkv with opus audio merged by MKVToolNix

[shaodan1997]

VLC version: 3.0.11
FFmpeg version: 4.3.1
MKVToolNix version: 49.0.0
Windows version: Windows10 1909
hardware: Surface Go Intel 4415Y/8GB/128GB/WiFi

Steps to reproduce:
1. Using FFmpeg to mix a mkv file with opus audio. I use a segment of Big Buck Bunny as an example.

Code: Select all

ffmpeg -i 'Big Buck Bunny.mp4' -c:a libopus a.mkv

2. Using MKVToolNix to remix a.mkv to b.mkv.
3. VLC can play a.mkv smoothly. But when playing b.mkv, there is about one second silence on the begin of video. And every time I drag progress bar, the silence appears too.

Other information:
1. I'm not sure whether this is caused by VLC or MKVToolNix. But VLC for Android also meet same issue, and it seems that other player(I tested Windows Media Player on PC and MX player on Android) can play b.mkv smoothly.
2. The choice of video encoding seems to be irrelevant. Both vp9+opus and hevc+opus meet same issue (I provide some samples).
3. Those mkv files merged by MKVToolNix with other audio encoding seems to not have this issue.

A sample package including logs can be downloaded from: https://1drv.ms/u/s!AngeRT2RKe4xgYBkIBi ... Q?e=iKfOWY