The VideoLAN Forums

Hi there,

I have been trying to pull back an audio to sync it up with the video in a .Avi file I've been watching. Unfortunately it isn't doing anything.

I have also tried the file in Windows Media Player Classic and had the same problem. Has anyone else come accross this?

Is there a solution?

It sounds like you may be trying to add a negative delay to the audio.

Obviously this is limited by the length of the internal buffer (cache) which is being used.
ie. if the buffer is say 300ms (VLC file default) then you can't add a negative delay longer than that (as the video would have already left the cache by the time the audio was due to be added).

You could try playing with the caching time under Preferences (Show All) - Input/Codecs - Access Modules - File Access (I assume you're dealing with file input).
This worked for me with limitations.

I found it difficult to get recorded AVI files to sync correctly if there are any discontinuities in the recording.

AVI stores the video and audio seperately.
If you have a discontinuous source (eg. converting a VHS home video to digital using a retail device) you will find that the audio continues to record (via the PC audio card) even when the video suffers a break (and stops recording due to lack of frame-sync).
The resulting AVI will have longer audio than video.
This leads to incorrect framerate information (as this is based on total video frames over the total recording time).
Even if you fix this you will need to re-adjust the audio delay at each break.
Eventually this delay will become unmanageably long.