Audio going out of sync

lumi-b wrote on 3/12/2019, 5:17 PM

Hi! First time video editor here and just hobby-level, really, and I got a copy of Vegas Pro 14. I have two cameras (GoPros) and a Sony recorder for audio. I do the "3 clap" thing and sync my two videos and audio with this clap sequence and everything is fine but several minutes later, I notice that my audio is out of sync with my video. Why does this happen? Do I have to do a "3 clap" procedure every now and again?

I am recording in-cockpit flights so the audio from the GoPros are useless once the engine is running and the Sony records from the aircraft's intercom so I don't know if an in-flight "3 clap" will even be picked up by the GoPros over the engine. My videos are usually over an hour long (no edits).

Any assistance would be great! Thanks!

Comments

klt wrote on 3/14/2019, 5:57 PM

Some of your devices are inaccurate. The longest thing I ever recorded using multiple devices was a Matthew passion, almost 3 hours long in one run. The cameras we used were pro or prosumer cameras, and there was no noticeable audio drift.

However cheap devices can have varying speed. At the moment I would blame your audio recorder, but both device may have very small inaccuracy which at the end sum up.

Can you do some dry-run tests in a silent room for as long as your usual flights?

Just clap around every 10 minutes.

Then sync that as usual, and see if the drift is constant?

If it is not constant I'm afraid there's not much help.

If it is constant, so the first claps are in sync, the second differs 10ms, the 3rd differs 20ms, 4th differs 30ms, etc, then you can do this:

Sync the first claps.

Then sync the last clap with ctrl-drag, so that length of your audio will change.

I'd expect this a very low percent change, say 99.997% or 100.002%. So you could ignore the pitch change, and just allow Vegas to pitch change locked to stretch.

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Just one more thing, before you start the procedure above:

I'm not sure what option you have on your recorder/gopro, but if the audio sampling rate don't match, try to set them to match. So both to 48000, or both to 44100.

Avoid having one set to 48000 and the other to 44100.

If you can't do that, you can still try what I already suggested. ;)