Why does changing fps of BOTH video and audio fix synch prob

[LisaB]

This is NOT an easy question, it is directed at experts who know something of AVI structure, interleave parameters, and maybe even divx structure.

I have a 25fps avi which plays perfectly on the computer, but on the standalone divx player (phillips 624) the audio slowly drifts out of synch.

I tried numerous approaches to fixing this problem. First I extracted the audio to wave file, then re-encoded to cbr mp3 using GoldWave, then remuxed with vdubmod...this didn't work.

Interestingly, I also tried re-encoding the video to xvid, then remuxing with the original audio...this worked! What this told me is that there was nothing wrong with the original audio.

Even more interesting, I converted the original mp3 to ntsc mp3 using BeSweet, then remuxed with the original video (changing framerate to 23.976 of course) using vdubmod...this worked!

I am stumped! Since I found a solution using the original audio, and a solution using the original video, I feel that it must just be some kind of muxing issue. How does one choose preload, and why is 1-frame the standard interleave? And is there some way that I could choose parameters so that the audio frames are not split across interleaves?

[Capmaster]

Moved to DVD Authoring forum

[LisaB]

This has to be a joke. My post doesn't concern DVD video, nor DVD audio.

[petar]

Just a wild guess. Maybe your standalone doesn't "like" divx at 25fps. Have you tried your original avi in another standalone apart from your pc?

[mats.hogberg]

My guess (forgive me, but I couldn't resist even if you're calling AVI experts only, and I'm not) is that your player plays the AVI in 23.973 fps even if it's a 25 fps AVI. The audio has no fps, so gets played in sync with the video if it was played at 25 fps. If I'm thinking this thru right, the audio ought to be ahead of the video after a while. Right?

/Mats

[Baldrick]

capmaster:dvd authoring?????

[LisaB]

Thanks for the stabs guys, but my standalone plays 25 fps divx just fine...lots of other 25fps divx/xvid have played without problem.

Also, the kind of drifting synch you'd get by playing 25fps divx at 24fps would be quite extreme, you'd be off by a full second after only 25 seconds of playing! No, the kind of synch problem I'm seeing is like a quarter of a second after about 6 minutes of playing.

Next things to try will be stripping and rebuilding the index (although I thought VDub did that every time you saved out an avi), interleaving every 2 frames instead of every 1 frame, and muxing with nandub instead of vdubmod, and maybe even resampling the audio from 48k to 44.1k

Also of interest is that the FourCC Description Code and FourCC Used Codec were both set to DX50. I changed the FourCC Description Code to divx, so that the avi would open in vdubmod. But this does make me question whether the FourCC code is right...maybe this is actually an xvid! I suppose there is no way of *really* knowing whether something is divx or xvid.
In the extended open options of vdubmod there is option called "re-derive keyframe flags" -- I'd love to know what that does.

Basically, I'd like to completely rebuild the avi as much as possible, without actually re-encoding the video...

Hey, maybe this post can keep on getting moved to different forums until someone comes up with a brilliant solution!

[Capmaster]

capmaster:dvd authoring?????

Saw this:

Even more interesting, I converted the original mp3 to ntsc mp3 using BeSweet, then remuxed with the original video (changing framerate to 23.976 of course) using vdubmod...this worked!

Missed this:

I changed the FourCC Description Code to divx, so that the avi would open in vdubmod.

Moving to Newbie Conversion