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I need some help or tips in the area of video and audio sync. Think a music videoclip, where the audio is recorded independently to create a master audio track and then the video will follow along. Not interested at all in the audio recorded with the videocamera.

I'm experienced with the audio part, but have done only one video project of this nature with iMovie (absolute noob and not willing to invest much in video editing software at the moment). While editing, it was an absolute pain to get everything in sync, lips motion with lyrics, ... I had to do it by hand drag and dropping frames around the audio track. Waste of time.

I was wondering if there's anything I can do while recording either the audio or the video that would easy this process. I do have semi-pro audio equipment with timing signals like SMPTE and things like that but I've never used them, not sure if they would be of any help for this.

Thanks!

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Haha! In movies about movies you always see this clap in the beginning of a shot. The one where the take number and everything is written on with chalk. And they hold it in front of the cam and make one loud clapping noise with it.

Well, if you have ever wondered what this ritual is for, congrats! You have found the problem to the solution ;-))

You get a video frame on which you see the clap closing and at the same time you can see the noise level peeking in the audio recording.

The poor mans version of this is to tell one of your actors to do the clap with her hands.

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  • Oh, and don't feel bad if you didn't now. They never tell you this in the documentaries. I didn't find this out either, until I started hanging out with film crews.
    – Paul Hänsch
    Oct 19, 2013 at 18:07
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There is a very expensive piece of highly specialized gear that can easily fix this problem....

It's called a boom box. :) The secret to doing any kind of sync like this is to finish either the audio or video first and then play one while you work on the other. You can insert a quick beep just before the beginning so that it can be easily matched in post. This is the point of that clapper thing they use at the beginning of film clips.

Simply lip sync to the audio that is playing and/or dub over the mouth movements using a script (depending if you are doing video after audio or audio after video.

Cheaper audio gear will sometime have problems with bad timing that will cause drift, but decent quality semi-pro or pro gear should hold sync well even with hour or more run times. If you do find that drift is a problem, try using a clapper or beep before the beginning and the end and then do a speed correction, which should work well as long as you don't have dropped frames.

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  • Thanks AJ. Yes, I work with the audio already finished and in a single track, then start cut and pasting my pieces of video one after the other, adding transitions, etc... When the scene is short, then doing this manually is not that bad, since there's not time for the audio and video to go very out of sync, but for longer scenes, it's incredibly hard to start the video scene at the precise millisecond so that after 30 seconds or more you start noticing a slight out of sync in the lip movement. Where can I read more about the technique you describe? Thanks again!
    – palako
    Aug 15, 2013 at 18:21
  • @palako If your audio is drifting out of sync that rapidly, something is seriously wrong in your process. Even fairly poor, old gear should only drift noticeably after a few minutes. Have you tried aligning the audio and video without editing and then using that as a nested sequence? Do you still end up with problems in sync even if you use a constant rolling clip with the audio rolling constantly as well? Are you sure you are not getting dropped frames? What kind of gear are you using for the audio and video?
    – AJ Henderson ♦
    Aug 15, 2013 at 19:11
  • By the way, if you want to be able to search for more details as well, the term for what we are discussing is dubbing because the effort is to sync a performance to an existing media.
    – AJ Henderson ♦
    Aug 15, 2013 at 19:18
  • Thanks, I'll find more info on dubbing. My sync problem is very simple and the root very obvious, I have a video track and an audio track, I manually try to get them to start at the same moment, but this is a drag and drop action on a very intuitive, yet non sophisticated interface, remember I'm using iMovie, so even if both sources run at their right pace with no gear or software problems, if they didn't start exactly when they should, they get out of sync.
    – palako
    Aug 16, 2013 at 7:12
  • @palako - that isn't correct. If you start off with, say a 30ms offset, that offset should not grow. The video and audio should run at the same rate and the offset should remain a constant 30ms throughout the entire video. If the amount of offset is changing (which it seemed like you were indicating is the case), then you have a much more serious problem.
    – AJ Henderson ♦
    Aug 16, 2013 at 14:17

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