syncing audio and video

[ande1718]

Hey, super newbie question...my friend recorded our drum teacher at 30 fps qvga with his digital camera and I recorded the audio with my Zoom H4 recorder at 16bit/44.1. After importing both to Pro Tools LE 7.4 the audio is slower than the video and after 65 minutes or so they are off by about 2 seconds. I tried the TC/E trimmer tool and was able to sync them up but the audio had to be squished too much and it sounded like (insert negatively connotated noun). I tried to lower the frames rate in the setup>session window but it didn't change the video at all.

For more loveliness my setup>session window does have options for pull up/down like the PT reference guide said it would. Anyway....help!

thanks a lot

[7161]

whats the frame rate? did you check that?

[georgia]

did you record the audio on the video camera video at 48Khz or 32 Khz... Is the protools session at 44.1k or 48K? How was the picture imported and crated. I doubt it was shot at 30fps probably 29.97 or 23.976. Is the video black&white or color, HD or SD? What was the frame rate of the editing station used to create the final video ( if there was one). And have you checked the audio from camera vs your H4?

Cheers
geo

[seanmccoy]

Isn't it most likely that he's just experiencing clock drift from using separate digital clocks? 2 seconds over 65 minutes isn't that much. I'll bet he can just varispeed the Zoom track up a fraction and it will sync up, and the amount will be so small as to be imperceptible.

[ande1718]

The Frames rate in the session and (according to my friend) of the camera was 30fps. There was no audio imported from the camera. I don't think there was any recorded with the original video, since he needed all the memory space for video (our teacher finished a few second before the memory card filled up).

The PT session is 24bit/48Khz. I imported the video with the import>video command in PT (I don't know what crating is unfortunately) and it came straight from the original file from the camera, no editing. The video is color. I doubt it was HD. I don't know what SD is. It was shot in QVGA if that is useful info. My friend described his camera as a "bridge camera," like a high end consumer digital camera, for taking stills and video as well. I wish I knew more details about it. All this was done in India while we were studying music so we just tried to put it together with what we had.

I could try varispeeding the audio, although if that has the same effect as using the TC/E trimmer tool (which shortens/lengthens the audio region while speeding/slowing the audio) the adjustment is too much and the audio sounds pretty bad.

Thanks for all your help, it will be a big relief to finish this project.

[seanmccoy]

If I'm doing the math right, the varispeed would be about five hundredths of one percent—far less than even a normal pull-down amount. Anyone who can hear that must be bionic.

[philper]

try SRCing your audio to 48k and try again. Over 65 min there would definitely be some clock drift between two devices w/ as flaky clocks as a Zoom recorder and a inexpensive video camera. The no-clock sync thing can work for sync sound up to 8 or 9 min, but for something as long as 65 min you need a more stable time-base for either or both devices (I have found). I know you wanted to save storage space for picture, but with any video shoot I recommend recording some scratch audio on the camera--even just thru the camera mic--to have as a reference in post.

Philip Perkins

[rhumphries]

Originally Posted by ande1718

The Frames rate in the session and (according to my friend) of the camera was 30fps. There was no audio imported from the camera. I don't think there was any recorded with the original video, since he needed all the memory space for video (our teacher finished a few second before the memory card filled up).

The PT session is 24bit/48Khz. I imported the video with the import>video command in PT (I don't know what crating is unfortunately) and it came straight from the original file from the camera, no editing. The video is color. I doubt it was HD. I don't know what SD is. It was shot in QVGA if that is useful info. My friend described his camera as a "bridge camera," like a high end consumer digital camera, for taking stills and video as well. I wish I knew more details about it. All this was done in India while we were studying music so we just tried to put it together with what we had.

I could try varispeeding the audio, although if that has the same effect as using the TC/E trimmer tool (which shortens/lengthens the audio region while speeding/slowing the audio) the adjustment is too much and the audio sounds pretty bad.

Thanks for all your help, it will be a big relief to finish this project.

The frame rate shouldn't matter. It started on video and ended on video-- there was no 2/3 pullup or down involved. It sounds like the amount of drift with a pullup/down; that would be 3 seconds 18 frames(29.97) over an hour, but I really doubt this. I think it's just crappy crystals running at slightly different speeds.

TC/E or varispeed at this small amount shouldn't make the audio sound _that_ bad.

I probably would use the time shift plugin. Find a sync point at the top and cut the audio region there. Find another sync point near the end and cut the audio region there too. Now in the time shift window either adjust the the duration or the end point so that it matches the length of the same sync points in your video. Write down the % of time shift, but don't process it yet. Now go back and extend the top and tail of your clip to the ends. Now type in that percentage that you found earlier and do the process. this should adjust the whole clip by the correct amount. Varispeed will probably sound a little better, and you are only changing the speed by about .05%, so you will never know the difference.

I hope that's clear enough-- it's a bit complicated if you've never done it.

-Richard


(this was actually much easier in the AMS Audiofile, believe it or not)

[danijel]

Originally Posted by rhumphries

Find a sync point at the top and cut the audio region there. Find another sync point near the end and cut the audio region there too.

extend this principle and add several (or 20-30) sync points throughout the performance (lock on strong, clearly visible drum hits). with as much speed variation, i doubt two points will be enough.

[jahtao]

You have two recordings done at the same time so you thought they'd be the same when you played them back.

BUT

In fact, based on the 2 seconds discrepency over 65mins you've described, it seems the two recording devices were running at 0.05128205128% different speeds.

This is normal.

(48kHz is never EXACTLY 48kHz in as much as your watch might have to be reset every once in a while, (ever hear of atomic clocks?)

In a professional environment digital devices are 'locked' together to avoid the problem you are facing.

But not to worry. You are lucky in that your Zoom audio is slower than your video. Just do a little edit every minute or so to keep the waveforms synced up. And then bounce it out or whatever.

If it was faster I'd recommend slowing it down with a non-timestretch algorythm (you know just resampling it) but the trouble is most processes don't let you put in more than 3 decimal places. And even those that do are sometimes lying to you, you get the same output with a +/-0.001 change.

Is he drumming in the video? Obviously make sure your edits don't ruin his groove. Try and get them in passages between him playing.

If its drifting by 2 seconds thats 60 frames. 1 frame is noticeable to the eye. Thus you need a minimum of 60 edits. Where drumming is concerned a 1 frame jump could be very noticeable to ear. 120 edits? : ) 1/2hr work max I'd say

Enjoy!
Matt

[ande1718]

Thanks y'all for your help, I sorted it out with the Time Compression/Expansion plug in. Another problem solved by the Slutz (trying to make it sound like the end of a sitcom mystery)