Any Tricks for Getting AV Sync Exact?

[4evrplan]

I've got a captured/edited/filtered video ready for it's final encode, but the sync seems juust slightly off somehow. It's not a framerate issue, because it doesn't get worse toward the end of the movie, rather the offset seems constant, so if I could figure out what delay (plus or minus) to use it'd be easy to fix. The trouble is I can't seem to get it just right. Does anyone know any good tricks for this? I thought maybe I'd load it into a subtitle authoring tool that shows both the video and wave-form, but I'd have to know exactly how the waveform should line up with the position of peoples lips on certain sounds. Anyone have any tips?

[4evrplan]

Maybe it's my imagination that it's slightly off. I've decided to live with it.

[redwudz]

If at some point you want to play with the audio/video sync, you could try playback with a player like Media Player Classic and use the sync adjustment to get it right. (View>Options>Internal Filters>Audio Switcher>Audio time shift) Then make note of the amount of offset in milliseconds shown there and add that to an offset for the file, plus or minus. Most video editors will let you put in an audio offset. I use VirtualDub most times. (Audio skew correction.)

There may be other ways to do it, other than by ear, but this is the method I've used. I try to find any sharp sound in the video, like a gun shot or a door slamming to adjust the sync to. Adjusting for lip sync isn't easy.

[jagabo]

If at some point you want to play with the audio/video sync, you could try playback with a player like Media Player Classic and use the sync adjustment to get it right. (View>Options>Internal Filters>Audio Switcher>Audio time shift)

You can also use + and - on the numeric keypad to shift the audio in 10 ms increments. Be sure to have the Status bar enabled so you can see the amount of shift there (View -> Status). For either of these to work you must be using the internal audio switcher (View -> Options -> Internal Filters -> Audio Switcher -> Enable...

[4evrplan]

I was doing basically the same thing with VLC, but MPC may be better if it uses 10ms increments. The increments in VLC are 50ms. Also, good idea looking for a sharp noise instead of watching lips.

[jagabo]

I was doing basically the same thing with VLC, but MPC may be better if it uses 10ms increments. The increments in VLC are 50ms. Also, good idea looking for a sharp noise instead of watching lips.

Sometimes sound effects are added in post so they might be out of sync in the original movie.

Another way is use an editor that shows the audio waveform along with the video. Then watch for an obvious sound like a gunshot. VirtualDub can show the audio.

Keep in mind that with 24 fps film every frame is ~42 ms.

[smrpix]

Keep in mind that with 24 fps film every frame is ~42 ms.

True, but in 35mm it can be slipped to the perf, so back to ~ 10.something. And with a sharp noise like a clapboard it's pretty easy to tell if the hit should be early or late within the frame.

[Budman1]

If there is a sharp noise as mentioned above something like below should work. I'm not quite done perfecting it yet but soon.



Sound approximately 10 ms into 35th frame 43ms in length


The upper part with the timings is complete but the lower part has not been incorporated yet. Would something like this work?

[hello_hello]

I use the MPC-HC/numeric keypad method, but without the source video for comparison (assuming you're correcting the audio sync of an encoded version) it's basically guesswork. My method:
I adjust the audio sync by +100ms and then by -100ms. One of them will probably make the audio sync look a lot worse than the other (assuming it's not actually correct), and will at least give you an idea regarding the direction in which the audio needs to be adjusted. Or sometimes it might be +/-200ms etc to be sure.

If you have the original, unedited file and you know it's correct....
I run the original in one instance of MPC-HC and the encode in another. I run them together, stopping and starting one until the audio of each is in sync. You can tell when it's pretty much synced as you won't hear any audio delay while playing both files and it'll produce a "phasing" effect. Once the audio is synced it's a simply matter of watching scene changes to see if they happen at the same time. If they do, the audio/video sync is the same, if they don't I stop both, adjust the audio delay of one, restart them, sync the audio up again....... it can be a bit of trial and error but you can get the audio/video sync of each to match within around 10ms that way.

By default, MPC-HC is set to pause/restart video using a left single click and switch in and out of fullscreen with a left double click.... a nightmare if you want to be stopping and starting videos very quickly by clicking on it to sync the audio. I change the fullscreen setting to middle click so a left click can only stop or restart the video.

If memory serves me correctly, after you adjust the audio sync using the numeric keypad, the adjustment happens slowly, so either wait several seconds before trying to re-sync the audio in the two video files or stop them both, adjust the audio delay of one, then restart them both and resync the audio again.