Synced audio track on MKV eventually becomes out off sync

[brent1a]

I'm using MKVmerge to add an audio track to a video file. They were out of sync so I delayed the video track by 3600ms or so and the beginning of the video is now in sync with the audio but by the end of the video the audio is out of sync again.
Do I need to 'stretch' the audio or 'stretch' the video?
.......or is there another solution?

[redwudz]

Most times you need to stretch or shrink the audio length to match the video length. I use Audacity for that. (Change Tempo).

[brent1a]

I just realized that while I had converted (detelcined) the video to 23.976fps from 25fps that I did not to the same with the audio. So I have been trying to mux audio that plays at 25fps with video that plays at 23.976fps....I assume that might cause some issues for proper muxing.
I'm converting the audio right now so we'll see what happens then.