Re: [SoX-users] wav speed up to match inverse telecine

[Doug C. <idi...@us...>]

>
> i am in need a means to 'correct audio' for  video that has been inverse
> telecine.(ivtc)
> basically i capure video at 29.97 - i can sucessfuly remove the 3 2 pull
> down making it the or (film) 24 fps ( 23.98 fps)
> but now the audio is out of sync.
>
> the video ( after some time like 10 min ) is ahead of the audio. I think
> this is because the ivtc basically throus away frames
>

How did you perform the ivtc operation? What kind of file are you working
with?

Adjusting the audio data is not the correct solution. ivtc should not affect
the length or playback speed of the media, so the audio data should not need
to change.

The correct solution is to adjust the video data to properly account for the
altered frame rate. If you remove frames but keep the frame rate at 29.97
fps, the video will play back too quickly and the audio will be out-of-sync.
This doesn't mean that the audio track needs to be corrected. Instead, it
means that the video track needs to be corrected so that the video player
uses a frame rate of 23.98 fps.

That said, there may be some other problem. Audio/video sync is easy to
screw up, especially with AVI files. You may want to look at a tool like
VirtualDub that can adjust the media file's frame rate to make the length of
the video track match the length of the audio track.