Old 11-14-2018, 07:45 AM   #1
mschnell
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Default Synchonizing Video to audio

As we now have this sub-forum....

Recently I needed to do a video of a concert. I used a hobby video camera and decent audio equipment. Then in Reaper I replaced the video sound by the much better (and processed) stereo audio. This did work decently, but needed quite a lot of time.

Later a friend told me that Magix can do this by pressing a button, automatically syncing the audio of the two sources and creating an appropriate video file.

Does Reaper or some script provide such automation, too ?

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Old 11-14-2018, 08:37 AM   #2
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This usually works with a clapping at the beginning of both the video and the audio record which then could be synchronized. But as you mostly have the audio source from the video file and the clean audio file from the PA recording, you could watch out for sudden peaks to find marked similarities on both audio tracks. Then its more easy to align both files.

I'm pretty sure there is no script for such cases but it could be done per peak matching. Maybe its possible to find a certain sequence of peaks in two different audio files. But I have no idea. Kawa, mpl, 2beat etc. could answer this.
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Old 11-14-2018, 09:31 AM   #3
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ReaPack/mpl_AlignTakes.lua is probably best "native" option here. But it works not so good for most people.
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Old 11-14-2018, 09:55 AM   #4
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would also multicam editing possible?
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Old 11-14-2018, 10:17 AM   #5
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It's usually not bad to do it by hand, even without a clap, especially if you enable spectral peaks
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Old 11-14-2018, 11:03 AM   #6
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It’s good to realize that as long as the audio is synched to within one frame, it will for all intents be lined up.

This is going to vary, based on the frame rate of the project. 24fps (cinema), as well as 30fps (most video cams) and 60fps can be encountered.

I usually sync my video and audio in a video editing program. Zoom in on the timeline to the frame level, and make sure the peaks match within the same frame.

Most videocams record audio at 48khz, so when recording audio for that purpose, I use the same sample rate.
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Old 11-15-2018, 12:33 AM   #7
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Quote:
Originally Posted by mpl View Post
ReaPack/mpl_AlignTakes.lua is probably best "native" option here. But it works not so good for most people.
No, this works fantastic. Didn't know about. Many thanks.
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Old 11-15-2018, 02:53 AM   #8
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In terms of sync there are thresholds to what humans find acceptable. It's based in our everyday experience.

Sound early, up to 1 frame or about 40 ms.
Sound late, up to three frames or about 100-120 ms.

This is due to us basically never hearing sound directly at the source, but slightly delayed. It's about 0.34 meters(bit over one foot) per millisecond of travel time through 20 degress Celsius air. Speed of sound is 343 meters/second at 20 C.

A person stands 3-4 meters away and talks to you. that's a 10 millisecond delay already. So we're used to that and can deal with it.

Never have your sound come too early, unless you really wanna fuck with people .
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Old 11-15-2018, 04:10 AM   #9
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Quote:
Originally Posted by airon View Post
In terms of sync there are thresholds to what humans find acceptable. It's based in our everyday experience.

Sound early, up to 1 frame or about 40 ms.
Sound late, up to three frames or about 100-120 ms.

This is due to us basically never hearing sound directly at the source, but slightly delayed. It's about 0.34 meters(bit over one foot) per millisecond of travel time through 20 degress Celsius air. Speed of sound is 343 meters/second at 20 C.

A person stands 3-4 meters away and talks to you. that's a 10 millisecond delay already. So we're used to that and can deal with it.

Never have your sound come too early, unless you really wanna fuck with people .
Sounds logical. Thanks for the info.
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