Trouble with audio sync

[Ryo94]

What cause the damned sync audio problem, all is ok in the first 20 or 30 minutes but after that begins the problem, This happens to me in Ulead MSP6, Premiere & VirtualDub using divx 3.11;4.12, MS Mpeg4 V1 & V2 and audio codecs Mpeg Layer III; MS ADPCM; PCM....anyone knows how solve this?
Greetings & Thanks for any help

[Airw0lf]

What is your exact process? Some hacked mp3 codecs can cause all sorts of bugs. Also, if you're splicing files you need to know whether you need aligned or unaligned splicing. Virtualdub can only do unaligned splicing, this caused me a lot of trouble initially, until i got around it somewhat with avisynth...

[Guest]

Also, if you're splicing files you need to know whether you need aligned or unaligned splicing. Virtualdub can only do unaligned splicing, this caused me a lot of trouble initially, until i got around it somewhat with avisynth...
How do I know if I need aligned or unaligned splicing? What is getting around it "somewhat", and how did you do it?

thank you,

[Airw0lf]

Here is my experience, and my interpretation, which may or may not be right. But it seems to work.

When you capture avis you get files where the audio track is slightly longer than the video track and vice-versa. This is not a problem when virtualdub is auto-segmenting avi files during capture because you know that all you need to do is add the segments together and everything will work out fine. (Since all the audio and video tracks run into each other in a logical way) This is essentially *unaligned splicing*.
However, say if you have a bunch of unrelated capture files (like me, most of the time) and you want to do some splicing/editing, the variation in the audio/video track lengths can cause trouble. You do not want to append these files together in an unaligned way, cos they are unrelated and soon you will lose sync because of this. So the best way to join these is by using *Aligned* Splicing, where BEFORE joining files, you trim/extend the audio stream to match the video stream. This way you don't get incorrect audio running into or out of other segments.

See this thread for more on this
http://forum.doom9.org/showthread.php?s=&threadid=18620

Previously I wasn't aware of this problem and kept getting massive sync problems 20/30 mins into my SVCD encodes. Doing Aligned editing with AviSynth solved my problems.
I have also had some good success by following this advice in the virtualdub help:

"If you are clipping the audio stream in any way through the video clipping options, it is strongly recommended that you uncompress the audio stream first, and use the Wav Audio… option to serve audio from the external, uncompressed file instead of the compressed stream. This gives you the cleanest and most accurate clipping."

So here are two possible solutions, hopefully this helps.