Synced audio track 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?

[johns0]

Please do not cross post,one thread is enough for one subject,this thread is closed