Drifting or out of sync ?

fosko wrote on 9/11/2014, 12:01 PM

I used the wrong setting on my camera and it spit the one hour video into 4 seperate files. At first I just bumped them together and it looked fine. But then...when I added the audio (which is one file) recorded seperately I noticed it was slightly out of sync and,,,it seems there are 3 frames missing between clips. A bit of a pain...but I can go to the MP3 file and cut that area out. It's not noticable visually and barely in the audio. But, even within the clip the audo seems to drift just a little. I'll study my camera a little more and not use that setting again...but can I expect to get drift even when working with one file ?

Comments

richard-amirault wrote on 9/11/2014, 12:05 PM

If the audio was recorded on a separate device (other than your camcorder) then YES you are very likely to have drift.

This all depends on how long your "take" is (a one hour video is more likely to drift than a ten minute one) and the accuracy of your two recording devices. Not every device, despite being 'computer' (or 'crystal') controlled, run at the *exact* same speed.

fosko wrote on 9/11/2014, 12:05 PM

OK I just double checked. Contrary to my prior beleif the audio from the camera was taken at 48kHz and the .mp3 was 44kHz. Could that be a factor ?

fosko wrote on 9/11/2014, 12:09 PM

Interesting. I was once told that since it's all digital it was all rock solid and would be the same speed.

The camera audio is using the onboard mic (this is just as reference). I'm using audio from the digital mixing board for the final product. From what I understand it records directly from the board onto a USB thumb drive. That file is then burned to CD and uploaded to our webpage...where I download it for the video.

richard-amirault wrote on 9/11/2014, 12:17 PM

From what I understand it records directly from the board onto a USB thumb drive. That file is then burned to CD and uploaded to our webpage...where I download it for the video.

So you are NOT working with the original file. That could also be a problem. It is goes thru, by my count, THREE variations/conversions before you drop it on your timeline.

richard-amirault wrote on 9/11/2014, 12:24 PM

In any case, I've had a similar problem and found it very easy to cut audio to re-sync with the video (that is if your audio is 'slower' than your video) You just find a good spot (no music or speech) and expand the timeline sufficiently to see the waveform and cut ... overlap just a bit to prevent obvious clicks or glitches.

If you have the camcorder waveform as well just match up the peaks and you are set ('till the falls out of sync anyway)

vtxrocketeer wrote on 9/11/2014, 12:25 PM

Interesting. I was once told that since it's all digital it was all rock solid and would be the same speed.

Nope. Not even in pro-level gear recording in the wild.

I often shoot long stage productions and capture to a high end audio recorder. I always have to adjust for a few frames of drift in post. My camera, a Sony FS700, is wonderful for video but lacks the ability to sync to an external timecode generator; neither does it output any timecode for sync purposes. Frustrating, but nothing that few minutes in post won't take care of.

fosko wrote on 9/11/2014, 2:19 PM

I guess this is another reason to, when I can, shoot shorter clips. These are sermons so I really can't have a gap. I have plural eyes3 but not very happy with it's results. Another option could be to run an audio feed directly to the camera (was trying to avoid the cables).

rraud wrote on 9/11/2014, 2:42 PM

You can also quickly divide a long event into shorter ones right in Vegas (keyboard 'S' key), and re-sync when drift is noticeable.

musicvid10 wrote on 9/11/2014, 2:45 PM

Every device, unless slaved by a sync cable, runs off its own internal clock.
Of course there is drift.

OldSmoke wrote on 9/11/2014, 2:57 PM

Fosko

I would first start by importing the files properly or "stitch" them together into one file. Depending on your camera, Vegas own "Device Explorer" might be able to import the files as one continuous file.

After you have it on the timeline, without any gap" add the MP3 file.

fosko wrote on 9/11/2014, 3:56 PM

I will try that. I've never used Device Explorer. Always moved files to my PC and used Project Media (import), but it is a Sony Camera,