How do i speed up audio?

Question

I need to fix up a video file. The video length is suspected to be 10:01.645. The audio length is 10:20.931. When i use virtual dub to combine the audio and video i can see its very far from sync. How do i speed up the audio so it matches the video length? I know it wont be perfect but its better then being +2 second off every minute. (at the 9minute mark its noticeable something is 15+ seconds behind)

Answer 1

If you can break the audio out into its own file, you can use Audacity to change the speed. It may take a little bit of trial and error, but for a starting point, +3% is pretty close to what you need.

1. Open the file in Audacity
2. Ctrl+A to select the entire file
3. Select Effect -> Change Speed... and enter the desired difference.
4. Click OK

Note that Change Tempo performs a similar function, and tries not to change the pitch. However, because it tries to keep the pitch the same, there will be some distortion, which may be undesirable.

Answer 2

Could you reduce the framerate of the video instead? Stretching audio often sounds strange, but altering the video framerate should come out the same.

Subtract 3% from the frame rate and it will match the audio.