Audio syncing

[lordretsudo]

Does anyone know of a good guide that explains how to sync an audio track to a video stream? I've done this in a basic sense in the past, adding a small delay or cut to sync things up, but would like to learn how to sync a film where the audio gradually goes out of sync as the film progresses.

I would really hope that there is some tool out there that allow you to see the video and edit the audio at the same time, rather than just editing the audio and guessing at delays, etc.

Any help would be most appreciated :-)

[poisondeathray]

What format is your video?

If it's a constant delay scenario (audio & video are the same length), you can try avidemux, and shift the audio on the fly, press preview, shift it some more etc...save it when it's fixed. Just check the audio shift and enter the +/- delay.

If it's a progressive sync issue, you generally have to shrink/expand the audio or video to match, then adjust for the offset. You can get a ballpark number by looking at the length (duration), then using the fraction of v/a or a/v . So either change the video fps, or re-encode the audio. You can often just put it into a mkv container and use the stretch function (for either video or audio) +/- the delay offset, this way there is no re-encoding or quality loss

The 3rd case is where there are discontinunities or desync points. These "blips" often bump the audio, and you have to process in segments, adjusting the delay for each individual segment (very tedious!)

[lordretsudo]

Thanks for replying :-)

The video source is a DVD, but I have demuxed the video segment, so it's a .m2v file.

I have an audio file that is about 11 seconds shorter than the video, though it doesn't look like anything is actually missing from the audio. It just gradually goes out of snyc as the film progresses. I was hoping to correct this by inserting a few small delays throughout the audio file.

[poisondeathray]

Is it in sync at the beginning (no offset) ?

Often its as simple as not properly decrypted, so try dvdfab hd decrypter or anydvd

Does the vob play correctly?

What are you trying to do with this? Encode to other format?

[Yobbo]

If you load both the original audio and the new audio into Reaper, you can line up the start and then stretch the new audio with alt-click to line it up with the end of the original audio (it's a high quality stretch, preserving pitch etc). Very simple - but invariably you will still find sync issues in the audio (even though the start and end are synced up). Like poisondeathray says, in this situation the only hope is to cut the new audio up into segments and adjust each segmentm which is a PITA. I haven't used tools like Hypercube Time Stretcher or SyncView, which may help in this process?