How do i sync video and audio with different lengths?

[PanMarSag]

Hello, can anyone tell me how do i sync video that it's length is 10:54, while the audio length is 10:36? This really bugs me out.

[ProWo]

are video and audio from different sources?

[jagabo]

First, to be in sync the audio and video don't need to be the same length in an AV file. They don't need to start or end at the same time either. On top of that, if you don't know the provenance of two recordings you may find that they are different in other ways. For example a movie released in one country may have scenes cut or added compared to the same movie released in another country. So simply knowing the length of the audio and video is not enough.

But lets take the case of a simple stretch or squish. The audio and video start at the same time and are initially in sync, but drift apart linearly as time progresses. In that case you can simply un-stretch/un-squish the audio. The 10:54 video is 654 seconds long, The 10:36 audio is 636 seconds long. So make the audio longer by a factor of 654/636, or ~1.028302. The audio and video will now be the same length. Most audio editors can stretch audio like this. Audacity, for example.

It's also possible to change the audio duration at the container level (no re-encoding required). MkvToonix for example:


[Attachment 62759 - Click to enlarge]

This tells the player to stretch/squish the audio during playback. Unfortunately, not all players respect this setting.