Audio out of sync and the desync keeps increasing as the movie continues

Help
1

Okay, so I had a movie in 1080p in english audio (mp4 format). I was like 1:25:17 in length.

I recently got a 4k TV and wanted to watch the movie in 4K (MKV format). I downloaded it but it wasn’t in english and also, the length was 1:25:25. I watched where the other 8 secs are and its in the end after credits so the audio is the same time length as the movie.

However, I used MKVToolNix to put the 1080p’s audio on the 4k one. It started off as synced and all good. But then it got a little out of sync and the desync kept increasing as the movie went on.

Can anyone help me out here? I played the movie side by side and the audio just gets out of sync idky.

thanks

2

This is unrelated to MKVToolNix.

Anyway, your issue is you’re applying audio that doesn’t match the length of video, so yes, of course it gets out of sync pretty quickly. You have to edit the audio first in something like Audacity changing its tempo to match the video runtime.