How to line up 4 separate video camera audio-tracks to a pair of sync claps ?

[studer58]

I have 4 camera video streams, all covering the same concert. A simple hand-clap was used at both the beginning and end of the concert (approx 1 hour 20 mins) to assist in lining them up later. I will strip the audio soundtracks out from each camera and line up the 4 audio files vertically in a Reaper project….aligning the beginning handclap precisely.

Due to there being no sync device or connection cable linking the cameras during filming, I’m expecting there will be drift between the audio streams, and the ‘end of concert clap’ probably won’t line all 4 up exactly. I don’t want to break the concert up into its component songs…I want to retain them as 4 long audio streams, for editing purposes.

Please note that I’m only working with wav audio files, which have been extracted from the 4 camera’s SD cards, not from their associated 4K video files (too big to work with and not necessary !)

How do I achieve the alignment of all 4 streams with the end-of-concert sync handclap ?

Thanks very much for your help !

[Philbo King]

I would start by verifying that there is drift. With the start claps lined up, how well the end claps match up? And do they line up with the end clap audio?

If not, you could assume the drift is linear (a fairly good bet), and alt-drag the right end of each Clip to match the video-clap to the audio-clap for each of the four video tracks. Then listen/watch the start and end of each song to see if they stay in sync throughout.

If they do not, you might have to add stretch makers at the start and end of each song so you can 'warp time' to slide video events to match audio events.

[vitalker]

Perhaps these will be helpful: https://forum.cockos.com/showthread.php?t=179544
https://forum.cockos.com/showthread.php?t=232672

[ashcat_lt]

Make sure that “Preserve pitch” (the one in Item/Take Properties) is OFF for each item when you stretch the things.

IME, this can be fiddly and annoying and iterative. You line up the beginning, then stretch the end, but then that causes the beginning to shift, so you go back and line it back up and then the end isn’t lined up anymore, so you keep going back and forth until you decide it’s close enough and give up.

In the end, you really need to listen to the result because that’s what actually matters and your eyes will only tell you so much. If I’m honest, I wouldn’t expect 4 different cameras at the same concert to add up to sound very good. You’ll probably end up picking the one that sucks least and maybe fill in with a little bit from another one, but I suppose you can’t know how it works til they’re somewhere close to synced.

[studer58]

Thanks for your helpful ideas everyone...unexpectedly it turned out that the files did sync up accurately enough with the beginning and end claps, without any stretching being necessary ! I found it hard to believe there was negligible drift, but such was the case.

I hope this issue-resolution process proves useful to other Reaper users in future...who may indeed experience the expected drift out of sync with multiple cameras that I was fearing.