Audio drifts out of sync

[Kalash109]

I am trying to edit an avi file in which the audio gradually shifts out of sync. Its fine at
the start then using mpclassic I offset +440ms after 45mins and its in sync but then the start
is out of sync. I have downloaded virtualdub/virtualdubmod and pgcdemux but am not familiar
with these programs. Any idea how to get this lot to gradually add an offset. I have searched and tried
various suggestions without success. Any help appreciated.

K109

[redwudz]

Usually when the sync error gradually changes during the playback of the file, this means the audio and video are different lengths. Offsetting won't help, you need to change the length of one or the other.

[Kalash109]

redwudz

Thanks for the quick reply. How would I change the length of the video
or audio and how would I determine by how much ?

K109

[redwudz]

You could check it with VirtualDub, File>File Information'. Or Gspot may show the difference between the video and audio lengths.

I usually save out the audio as a WAV file with Full audio processing with VirtualDub Mod. The drop the WAV into Audacity and modify it to match the video length. Then you can convert to MP3 CBR and add it back in, or just add the modified WAV back in if you are going to encode it to MPEG.

Or you can change the framerate of the video, but that can cause other problems.

And it depends on why and how it's out of sync. Sync problems can be caused by MP3 VBR audio, bad cuts and joins, bad framerate conversions such as PAL<>NTSC, or a corrupted video or audio file. Or, worst case, a combination of the above.

[Kalash109]

Thanks I'll try what you said and see if that helps

K109