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Tech: How can I synchronize concert videos?

GUEST,Grishka 22 May 13 - 06:26 AM
GUEST,Stim 22 May 13 - 09:47 PM
GUEST,Guest 23 May 13 - 03:44 AM
GUEST,Grishka 23 May 13 - 11:09 AM
GUEST,David, previously guest,guest 23 May 13 - 01:26 PM
GUEST,Grishka 23 May 13 - 06:05 PM
Tootler 23 May 13 - 07:50 PM
Bill D 23 May 13 - 08:32 PM
Tootler 24 May 13 - 05:07 PM
GUEST,Grishka 25 May 13 - 11:18 AM
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Subject: Tech: How can I synchronize concert videos?
From: GUEST,Grishka
Date: 22 May 13 - 06:26 AM

The following problem must be familiar to many Mudcatters: I have a professional sound recording and an amateur video - with camera sound - of the same concert; now we want to use the recording as the video soundtrack. A quick Google research, including Mudcat and some self-declared experts, showed advice such as "clap your hands once before the concert, or look for singers pronouncing consonants ..." - very tedious and imprecise. Software should do it automatically, searching the two sound tracks for matching frequencies etc., and skipping or doubling single frames whenever necessary. I guess thousands of YouTubers do it like that, whereas tens of thousands do it the tedious way.

How do the real experts proceed? What video software does it best, and cheaply? (Unfortunately I have never used such software at all, and none of my friends is an expert. The software descriptions I have read are not helpful either.)

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Subject: RE: Tech: How can I synchronize concert videos?
From: GUEST,Stim
Date: 22 May 13 - 09:47 PM

The way that the audio and video are synchronized for film, TV and the like is that each is recorded using a marking system called
SMPTE Time Code which basically puts a mark on each video frame that corresponds with on mark on the tape, allowing each to be connected during editing.

It is helpful to understand that much of the music we see on film and television is recorded either beforehand, in the case of musical numbers, and lip-synced, or afterwards, as in the case of background music. Also helpful to understand that when events are filmed, there generally is a camera shooting silent, asynchronous footage that can be edited into the master footage.

As to your project, there are ways to do it without having recorded using SMPTE, but there will be a lot of tedious, imprecise, cut and paste.

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Subject: RE: Tech: How can I synchronize concert videos?
From: GUEST,Guest
Date: 23 May 13 - 03:44 AM

I've done this sort of thing in an amateur way on avi files using virtualdub and audacity - not perfect but not as tedious perhaps as your post suggests.

Clapperboard markers would help, but this is what I did:
(Recordings need to be digital to have a chance of timings matching and should have the same sampling rate.)

Make an avi of the section of video I'm dealing with.
Extract the audio from the avi using virtualdub.
Load the resulting wav file into audacity.
Load the good quality audio as a new stereo track into audacity alongside the camera audio.
Using the waveform graphics as a guide, position the good audio to match the camera audio - in audacity I can zoom in to help get it as close as possible. (How easy this is will depend somewhat on how good the camera audio is - the less extraneous noise the better.)
Silence the camera audio track(or edit it to mix in some ambient noise if desired).
Export the result. I now have an audio file to match the video.

Now I run virtualdub using the new audio file as the audio source (go to the audio menu to load it) rather than the audio from original video.

Make sure I've set my compression options (for video and audio), in virtualdub you can create processing settings files so I can effectively create my own presets.

Use the output play button and window to preview the result. Make sure I check at a point near the end as well as the beginning - sync issues can be incremental. If necessary, fine tune using the interleaving option in the audio menu. I found getting the mouth movements of vocalist looking right is the more important thing to use as a guide with this - you notice this more than you do other stuff.)
Now I save the new avi.

Without using expensive equipment, software and expertise I don't think you'll find an easy way to do it. This way is free and I'd imagine about as easy as it will get.

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Subject: RE: Tech: How can I synchronize concert videos?
From: GUEST,Grishka
Date: 23 May 13 - 11:09 AM

Thanks, Stim and Guest. I should have mentioned that the video material is digital, presumably in avi format (I cannot check that at the moment).

I have just downloaded and tried VirtualDub (the first time ever I operated a video editor!) and found that it can export the audio and import new one alright, even of differing sample rates, and stereo for mono. I created a short test video with my own (photo) camera and home recorder and proceded principally as Guest suggests, with a perfect result.

Two problems remain, in my eyes:
  1. "Position the good audio to match the camera audio" initially - works OK by staring at the wave forms, not too tedious, but may well be supported by some VST plugin (who knows of any?). Converting sample rates should be available in most software including Audacity.
  2. Much more importantly: if the timing of the two devices differs, the two audio files may lose their initial synchronousness. I don't know to what extent that applies to the material I am speaking of; I guess it will not be as bad as with former mechanical stuff for which SMPTE was invented, but it may well become noticable if the material measures in hours. As I wrote, ideally the video should be adapted automatically, which of course means that the video software should do it. If the user must do it manually, it will be very tedious, even if we assume just a linear factor (- I wonder if I will manage). To adapt the audio would be a shame.
Anyone more ideas and recommendations?

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Subject: RE: Tech: How can I synchronize concert videos?
From: GUEST,David, previously guest,guest
Date: 23 May 13 - 01:26 PM

I found that my method only worked doing one song at a time - through a whole set timing discrepancies build up. But then if you're uploading to youtube etc. that's probably what you'd want anyway.

Video tends to use 48000khz as it's the dvd standard Computers set 44100khz, the cd standard, as their default usually. I've always tried to make sure sampling rates are the same when the recordings are made in the first place. I did a quick experiment and found that Steinberg Wavelab LE will convert the sample rate and seems to do it cleanly. I think you can get it for free - I got it bundled with some hardware I bought. I don't think audacity does it.

My trick with audacity was to place the "good" sound on the early side initially and find a single point I could match on both audio files. Then select a section matching the length of the difference between that point on each track. Zoom in, to get that as accurate as possible. Copy that and paste it in at the start of the track. Before it's deselected, silence the bit you added. This will push the good sound into place fairly precisely. It's a rather sticky tape and scissors technique but it does work.

I don't know anything about VST plugins.

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Subject: RE: Tech: How can I synchronize concert videos?
From: GUEST,Grishka
Date: 23 May 13 - 06:05 PM

I think all software can convert sample formats, though usually with some additional loss of quality. This should not matter if I do not use the old soundtrack at all: My new soundtrack will be bit by bit equal to the sound recording, suitably truncated at both ends.

On reading more of the users' manual for VirtualDub, I realize that this software actually can resynchronize the visual material according to some time marks similar to SMPTE, as I hoped it would. I don't know yet how to trigger this behaviour from my sound recording, and how to recover the corresponding information from the original video, but I hope to find out.

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Subject: RE: Tech: How can I synchronize concert videos?
From: Tootler
Date: 23 May 13 - 07:50 PM

I use a similar approach to Guest, David (aka Guest, Guest) but with different tools. I am a Linux user, so the tools I use reflect that but the principles are the same.

I use ffmpeg to extract the camera audio. This is a command line tool and will convert just about anything to anything else. It is available for Windows as well as Linux. There is a GUI called WinFF which basically works as a front end to ffmpeg and enables you to drag and drop the files you wish to convert. I had a quick look at the ffmpeg manual and it looks as if it will convert audio sample rates.

I generally use this for You Tube videos, typically 2 - 4 minutes long, nothing as long as a whole concert. I find a specific point on both the audio recording and the camera audio which I can clearly identify then line those up in Audacity, zooming in as necessary to the get the alignment as accurate as I can. I then play back both together. If the two tracks are accurately aligned, they should sound "as one". If they start to drift apart you will get an echo effect. If you can identify where that starts, you should be able to realign. I've not had that problem with the short videos I make so have never needed to deal with it.

Once I have the camera and actual audio accurately aligned, I then either trim the audio so it starts at exactly the same point as the camera audio or (most commonly as I always start the audio recorder after the camera), I add a short section of silence to the start of the audio track to align its start with the start of the camera audio. Once I've done this I either remove or mute the camera audio and export the audio from Audacity. It's important to export to a lossless format so there is no loss of quality (I normally use Flac, but Wav will do just as well).

My video editor (Open Shot, a Linux tool, though they have plans to port it to Windows and Mac in the near future) allows me to silence the audio in a video track, so I can then add in the separately recorded audio track and line the start of the two tracks up. If you have lined the start of the video and audio tracks up accurately, the two should be in sync. I find it usually works fine but occasionally, they go out of sync when I export the final video, in which case it may be a matter of shifting the audio track very slightly so they are in sync.

Even worse, sometimes they go out of sync when uploaded to You Tube, but there doesn't seem much you can do about that, though deleting your uploaded video and re-uploading it seems to work.

I can't comment on audiodub but I reckon it will largely work in much the same way.

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Subject: RE: Tech: How can I synchronize concert videos?
From: Bill D
Date: 23 May 13 - 08:32 PM

Avidemux may help with some of the editing

and Avanti may be another useful front end for ffmeg.

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Subject: RE: Tech: How can I synchronize concert videos?
From: Tootler
Date: 24 May 13 - 05:07 PM

I know there are some who like avidemux. I tried it and found it buggy, but that was some time ago and it is probably much improved now.

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Subject: RE: Tech: How can I synchronize concert videos?
From: GUEST,Grishka
Date: 25 May 13 - 11:18 AM

Thanks, Tootler and Bill. The idea of the project mentioned in my OP is to keep the sound recording of about 1 hour completely untouched, quasi documentary, and to adjust the video if necessary. (We currently don't plan to upload it anywhere, just burn it to DVD-Roms.) I will research about the synchronization tags in the AVI format. Further hints are welcome.

I have downloaded Avidemux as well, but not tried it yet. Its emphasis seems to be on the variety of video formats. Has it more to offer than VirtualDub for our project?

Typical YouTubists, and those who perform a sequence of short songs and edit their sound anyway (e.g. shorten the pauses), will probably not run into any synchronousness problem; of course they have to synch each song separately.

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