Delay or advance (shift/sync) individual tracks (+- seconds)

[zaza42]

Please add an option for setting audio delay, a.k.a. changing a/v sync!

Edit by @mifi :

Seems this can be done with -itsoffset:

• https://superuser.com/questions/982342/in-ffmpeg-how-to-delay-only-the-audio-of-a-mp4-video-without-converting-the-au
• https://trac.ffmpeg.org/wiki/UnderstandingItsoffset
• https://wjwoodrow.wordpress.com/2013/02/04/correcting-for-audiovideo-sync-issues-with-the-ffmpeg-programs-itsoffset-switch/

[mifi]

Then we need to -ss differently for audio vs video. Not sure if this is easy. Maybe something like this:
https://stackoverflow.com/questions/55147398/how-to-specify-an-offset-and-a-seek-position-for-a-video-stream-of-a-mp4-contain

Update: https://wjwoodrow.wordpress.com/2013/02/04/correcting-for-audiovideo-sync-issues-with-the-ffmpeg-programs-itsoffset-switch/

[zaza42]

@mifi : Yes, this is what i exactly use.

Another solution with small tempfile: https://superuser.com/a/1307386/607525

[chasylexus]

Searched exactly the same.
My use case:
I have screencast without audio and audio corresponded to screencast. Audio begins with several seconds of silence and should be synced with video before merging. It will be super-nice to have this feature.
Sometimes audio also have a little bit high speed that video (several seconds after several hours) and should be scaled but this is not so common case I think.

[mifi]

https://wjwoodrow.wordpress.com/2013/02/04/correcting-for-audiovideo-sync-issues-with-the-ffmpeg-programs-itsoffset-switch/

[Binger-cn]

I need this option very much !
I often shot badminton matches, each time result in mp4 files usually 40GB+ per file. However, I used bluetooth audio devices, so that audio is 200ms later than video. And I need to cut each file into 200+ segments for later use.
I used LosslessCut to cut the original file, but in each segment the audio is still delayed 200ms. The solution I'm now using is that first I use mkvtoolnix to create a temp file, also 40GB+, and cut the mkv file in LosslessCut. This procedure really costs too much time and disk space.
So I wish LosslessCut could provide an option to delay an audio track some miliseconds, with a positive or negative number.

[mifi]

FYI @gyarmish posted a manual workaround for adjusting individual tracks, see #929 (comment)

[gyarmish]

Thanks for that mention mifi.

In addition to its usefulness - part of the reason for the post was to show how it can be implemented in a new release - its quite tedious manually but it can be automate this behind the scenes using the standard lossless functions.

Imagine having to do that for multiple short videos. It will get done but but if those steps can be programmed in it would be very useful.

[mifi]

Yes if I cannot find a way for ffmpeg to shift the offsets, then extracting, cutting and re-importing individual tracks like you outlined could be a workaround however I would imagine that it's much slower (more CPU/resources) than letting ffmpeg do it internally