(Studio 12 mp4 640x480, 29.97fps)

Earlier this week I uploaded a 40 minute SD piece (640x480 resolution, 29.97fps). I noticed that AV sync is good towards the beginning but became increasingly off with time. Near the end, the LipSync was off by seconds.

My initial compression was mp4, but seeing the problem, I reencoded the piece into Divx (640x480) and replaced the clip. Same LipSync problem.

Having posted similar SD clips of 40 minutes or longer, I know that this works with Divx (320x240 res). So I reencoded the clip again into this lower resolution and replaced the file. Sure enough, at this resolution, LipSync is dead on.

This test clip consists of a talking head (of Clive Thompson) for 13 seconds followed by black for 47 seconds. The sequence is repeated 40 times to get near the 40 minute mark. There is burn-in timecode so during the black out, you can see that it is still playing.

This version is mp4 640x480 resolution. The same clip with Divx 320x240 resolution can be found here:
vimeo.com/2412636

The forum discussion on this is:
vimeo.com/forums/topic:9128