Audio track going out of sync when converting

[carlmart]

As I do all video library using AC3 5.1 as audio codec, sometimes I extract DTS tracks with Audacity, and then export it as Dolby AC3.

But today I found a video that has a DTS XLL audio track. After converting it and putting the AC3 audio track back with MKVmerge (the way I always do), I found audio had gone out of sync.

And it was not the same out of sync on two different videos I tried. One was just 400mS and the other several seconds apart.

Then I made a complete (video/audio) conversion with Vidcoder, and there was no out of sync.

Can someone tell me what holds the sync together with that type of DTS codec? I say that because that never happened to me before, and I probably made hundreds of conversions like that, as they save a lot of time.

[hello_hello]

There could be gaps in the audio that aren't accounted for when it's extracted (eac3to is the only program I know of that accounts for gaps when extracting).