Synchronizing audio/video with FFMPEG

[beyondthegrave]

Hi,

I was given separate audio/video files in AC3 and M3V formats and need to merge them into one FLV file. I already know how to merge audio/video to FLV, I just need to synchronize them.

The audio file is for some reason is shorter than its matched video file. The audio file is 5:38 and the video is something like 6:30, so essentially I want to:
(a) stretch the sound so it is 6:30, or
(b) squish the video so it's 5:38

I saw the vsync and async parameters, but can't figure out exactly how to do it right.

Anyone know how to do this?

Thanks for any help you can offer.

[guns1inger]

Unless they originally came form the same source and one has been stretched or compressed, I doubt you will ever syn the two.

Simplest option is to convert the audio to wav, load it into audacity and stretch it to match the running time of the video. Then use the pitch shift function to make it sound right. Save it as a new wav file, convert it with ffmpeggui or aften to get AC3 again, then convert (or just use the wav file - if you are converting to flv anyway, you don't need AC3 audio)

[beyondthegrave]

That's a good idea. But when I tried it, I realized that the sound is the right speed, it's the video that is stretched out. When I stretched the sound to match the video, it sounded painfully slow.

So can I use ffmpeg (vsync option) to squish the video? Or is there another video tool I can use?

Thanks a lot.