Help! audio sync question

[lakedude]

I use FU for divx video, graph edit for mp3 sound, and Virtual Dub to mix the sound and video together. About half the time the sound and video files are the same lenght time wise and can easily mixed. About 40% of the time the audio frame rate and the video rate are off and in these cases the video rate needs to be adjusted from 23.976 to 23.978 (usually) or 23.977. Sometime the rates are way off and one time the first half was at 23.976 and the second was beteween 23.974 and 23.975 with neither hitting right on the money.

My question is what causes the rates to be off? Is it Lame MP3? Is it dropped video frames? What is going on? It is not really a big deal cause 90% of the time a simple rate correction will fix the problem but sometime a whole bunch of manual tweeking is needed and is a real pain in the butt. Even if I can't fix the problem I would like to know what causes it.

Remember if you ain't Muslim you ain't Shiite.

 

[lakedude]

I just did a capture to Mpeg2 using a ATI AIW Radeon. The Mpeg2 turned out fine so I wanted to convert to Divx using Nandub for the video and lame mp3/graphedit for sound. The two files were way off and I could not get them to sync manually. If the beginning and end were in sync then the middle would be off.

The way I fixed the problem was to use Flask at the highest quality setting for divx slow. The results were in sync but the file was still too big. Lastly I ran the Flask results through Nandub selecting avi audio and recompressed to my desired file size. This works but is a pain is the ass. Anybody know a better way?

Remember if you ain't Muslim you ain't Shiite.

 

[Guest]

You can try to capture using a device called TBC (Time Base Corrector).
This will fix errors in the video stream that are often known to create ausio sync problems on final material.

This is valid if you are capturing from VHS or other not professional analog source.