I extracted a DTS track (DTS, 6 chan, 1536 kbps) from a video to add it again as secondary track as AC3 (lav) set to 640 kbps. Now this newly generated ac3 track is out of sync - any ideas how to fix that or why that is the case since it is the same video i extracted the track from.
Is it possible to achieve sync by shifting the audio track? If so, please use it.
If A/V offset is growing like when some packets are dropped because they are e.g. damaged, there is nothing we can do about it. Operating with raw compressed audio streams means that there are no guard rails of timestamps otherwise provided by the container.
If video has a high resolution or video display in Avidemux uses a slow unaccelerated fallback path (the "Qt" renderer) and video gets behind audio, this may be a performance issue which won't affect a proper video player once the audio track gets muxed into the container.