How to sync audio?

SpiritSharD wrote on 1/14/2015, 9:32 AM
I'm a complete novice and am struggling to sync audio tracks for my videos.

I record gameplay which is going to be uploaded to Youtube after editing/rendering. I've dabbled in it before and usually have been okay.

For this particular video I am having difficulties. The video of the game alongside the accompanying video are synced correctly as they were both recorded together using the same program (MSI-Afterburner). However, audio from Skype which I recorded using a separate program (Evaer) is what I'm having difficulty with.

In short, some times the Skype audio seems perfectly in-sync with the game video/audio, but other times (later on in the video) it doesn't. For example, one of my video clips is of a game called Counter Strike. At one point I kill an enemy and my friends react to it; I have this sync'd pretty well. However, very late in the video there is a shoot-out, however gunshots playing through someone else's speakers which you can hear in the background does not align correctly with what the gameplay video/audio is displaying. I'm probably explaining this pretty bad.

This is without rendering, it's all during editing. Anyone have any suggestions?

Comments

c3hammer wrote on 1/14/2015, 10:21 AM
There are a couple of options for syncing audio. I'm guessing the problem is due to ever so slightly different clocks in your different devices, or a difference in latency of the streams across the internet. This issue often comes up when recording with multiple cams on long presentations as well. The cams just aren't perfectly matched clocks vs their encoding and their playback rate is not exact and can be clearly seen after an hour and even less some times.

1. Cut up the Skype track and match wave forms. Just put the peaks of the gun shots on top each other. This is the only option if this audio goes in and out of sync.

2. Lengthen or shorten the Skype track until the later action matches with your other captured video. This will be some trial and error to get it close. Opposite click => Properties => Time Stretch on the audio track and/or Play Back Rate if it's both video and audio out of sync.

Cheers,
Pete
D7K wrote on 1/14/2015, 11:14 AM
You could try the trial of PluralEyes and see if that works for you. Great program, but fairly expensive program if you don't do a lot of syncing.
richard-amirault wrote on 1/14/2015, 2:51 PM
When tracks are in-sync at the beginning and out-of-sync later on it is usually because of different clock speeds. Not every device records at the exact same speed.

If you have some reference point to match in both audio tracks it should be fairly easy to sync. With audio from a video game it would be harder than a 'live' video but it does seem to be doable. When one track is synced at the beginning but not later on ... you can edit the lagging track by cutting out a small segment. (I usually overlap the cut out segment slightly as it makes it less obvious there is an edit there) This is much easier on an audio track than the video track. It is also less obvious to do many small edits rather than one or two big edits.
musicvid10 wrote on 1/14/2015, 3:49 PM
Cut into 10 min chunks, always in quiet zero-crossings.
Line up the chunks using peak waveforms.
Chienworks wrote on 1/15/2015, 6:43 AM
If both tracks are running at a constant speed, just different speeds from each other, then there should be no need to do any cutting into chunks. In fact this would be a very bad thing to do, as well as a huge waste of editing time. Align the beginning, then Ctrl-drag the end of the skype audio track to the left to speed it up or right to slow it down to match the other audio. With a little practice this can take a few seconds. I have this situation whenever capturing from VHS tapes. The audio encoder in my A/V->DV converter fried so i record the audio through another device who's clock speed is slightly different. I end up with audio that is about 12 seconds per hour slower than the video. Aligning the beginning and Ctrl-dragging the audio track back to the left 12 seconds per hour aligns them perfectly.

Ideally you should also go into properties for the audio clip and set the pitch change method to "lock to stretch" so that the pitch changes proportionally with the speed change.
bsprague wrote on 1/15/2015, 10:16 AM
I ran into a creative approach using the free Audacity program. The demo involves using the "other brand" of software, but the method should apply here.



musicvid10 wrote on 1/15/2015, 10:54 AM
"If both tracks are running at a constant speed, just different speeds from each other,"

In all my years syncing audio from live shows, I've never seen that.
Any two clocks not synced by a wire or telemetry will drift. The rate of drift is not a constant.
Identical camera models or h4n and you "may" be able to get around cutting, but done intelligently, chunks are still preferable to any form of stretch for critical listening.
Any Q-noise and flanging are absolutely intolerable to me while listening to music.
Chienworks wrote on 1/15/2015, 12:42 PM
Well, i've never had a problem with the speeds not being constant.

Just keep in mind that if you go with the chunking method you won't be correcting the pitch, so that too will be an audio defect to be dealt with.
musicvid10 wrote on 1/15/2015, 12:56 PM
I've never found that to be a problem, either.
;?)