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Offline techgui

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A/V sync problems
« on: December 20, 2013, 01:07:40 PM »
Earlier this year I recorded a show with one stationary canon Vixia HF R10 camcorder and a Tascam Dr-2d audio recorder patched into the board.   The recording is one hour long.  When I place both the camcorder footage with audio and the tascam audio onto the Sony Vegas time line I'm having problems with sync.  For instance at the beginning of the track, I sync the canon track with the tascam track.  After several minutes into the recording the tracks begin to loose sync.  I had to split the canon track several times over the hour long track to keep it in sync.  Anyone know if this is a Tascam problem or a Canon problem?  Any fixes? 

Offline Gutbucket

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Re: A/V sync problems
« Reply #1 on: December 20, 2013, 01:36:18 PM »
Not a problem with the equipment. It's simply that the two recordings were made with different clocks which were not sync'd.  When they are played back using the same clock, those differences make the two recordings run at slightly different speeds.*

You'll need to manually sync the two recordings.  That can be done in a few different ways.  You can do it like you've done, cutting up one recording into shorter segments which are not long enough to notice the drift, and aligning each. Or you can do some calulations and change the sample rate of one slightly to compensate for the timing drift.  Or you can use an editor with a 'shrink/stretch' type function which is the easist way to do it. I use Samplitude and it's pretty straight forward to shrink the longer file to match the shorter one by aligning a transient at the begining and very end of the file.  I don't use Wavelab but I think has a similar function, I'm sure other editors do as well, not sure if Vegas does, but look into that.  Someone will probably chime in who knows if it does.

*Not that it helps you with this, but if you were to play the two recordings on the devices with which they were recorded, manually sync'ing the two at the start, they would stay in very close sync for the entire hour.  That's because the files would be played back using the same clocks with which they were recorded and the differences between them wouldn't matter, only the consistency of each clock with itself from recording to playback would matter.
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Offline techgui

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Re: A/V sync problems
« Reply #2 on: December 20, 2013, 02:15:29 PM »
Vegas does have a shrink/stretch function, but I haven't verified the the sync problem is linear.  I don't have the original files, so I will have to set up an experiment.  I'm concerned because I've been asked to do that production again this March.  Last March I wasted several hours syncing the 3 cameras for this production.

Offline 2manyrocks

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Re: A/V sync problems
« Reply #3 on: December 20, 2013, 02:36:35 PM »
Look at Cyberlink Powerdirector 12.  the $99 version and up will sync one audio source and up to four cameras automatically.

I used it last night to sync 38 minutes of camera video with audio from my 2d. It worked so well that I have no idea whether there was actually any drift between the camera video and the audio before processing the video. 

  I stopped using Sony Movie Studio Platinum 12 once I got the Powerdirector software.   

Offline techgui

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Re: A/V sync problems
« Reply #4 on: December 20, 2013, 07:47:45 PM »
I don't believe the problem is Vegas 11 Pro. 

Offline techgui

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Re: A/V sync problems
« Reply #5 on: December 21, 2013, 03:05:00 PM »
I did an experiment.   Turned both the camcorder and the Tascan Dr2d on for 47 minutes.  Every five minutes of so I used the clapboard to record a sync mark.  The files were then imported to Vegas 11 Pro.  At this point I manually synced them on the first clapboard mark.  I then measured the time between the last clapboard mark on the camcorder file to the last clapboard mark on the tascam file.  The Tascam audio file was 3.4 seconds longer.  As Gut bucket suggested, I split the longer audio file at the clap board mark and used the shrink function to line them up.  The good news is it lined them up pretty well, but not perfect.  Unfortunately as I scroll thru the tracks the drift problem is not perfectly linear. 

Offline 2manyrocks

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Re: A/V sync problems
« Reply #6 on: December 22, 2013, 12:08:09 AM »
A while back, I did about the same test of a DR2d and a Canon HF M500.  About 60-75 minutes, there was enough drift to create an echo effect, but I don't recall there being 3.4 seconds worth of drift. 

The audio sample rate is set the same on your 2d and your camcorder?

Wonder if you could video an atomic clock countdown on your computer screen as a reference to both units? 

Offline techgui

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Re: A/V sync problems
« Reply #7 on: December 22, 2013, 09:24:16 AM »
Not sure about the sample rate.  The Dr2d is set for 48khz, not sure what the Canon uses.  I'll try running "MediaInfo" on the files later to verify.   

I will also try setting my camcorder to record smaller files to see how well they sync.  When I do this, I will also record the world clock along with the clapboard marks to see which device is drifting. 

I was really hoping PluralEyes would do all this drudge work.....

Offline techgui

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Re: A/V sync problems
« Reply #8 on: December 22, 2013, 10:23:07 AM »
Sample Rates per MediaInfo

Canon Vixia hf-r10  256KBPS 48KHZ 16bits ac-3
Tascam Dr2d  1536KBPS 48KHZ 16bits PCM

Offline 2manyrocks

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Re: A/V sync problems
« Reply #9 on: December 22, 2013, 03:11:29 PM »
Here is a screenshot of my Canon m500 v. DR2d test.  The click on the Canon appears at 1:05:47:14 and then appears on the 2d at 1:05:47:17, only a few hundredth's of a second later after running for over an hour.

I'm curious to see what your testing shows. 

runonce

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Re: A/V sync problems
« Reply #10 on: December 22, 2013, 03:43:46 PM »
So it's a classic case of sample rate drift between two devices set at the same rate....minor differences add up.

Since - I assume the camera audio and video are already synced - just shrink the DR2d source to match...

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Re: A/V sync problems
« Reply #11 on: December 22, 2013, 05:16:56 PM »
A few posts back, the OP mentioned that his files were 3.4 seconds out of sync in a 47 minute recording.  That seems abnormally high.

runonce

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Re: A/V sync problems
« Reply #12 on: December 22, 2013, 06:28:32 PM »
A few posts back, the OP mentioned that his files were 3.4 seconds out of sync in a 47 minute recording.  That seems abnormally high.


True  - Your independent tests seem a little more like one would expect...

Offline Gutbucket

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Re: A/V sync problems
« Reply #13 on: December 23, 2013, 09:38:06 AM »
Sample Rates per MediaInfo

Canon Vixia hf-r10  256KBPS 48KHZ 16bits ac-3
Tascam Dr2d  1536KBPS 48KHZ 16bits PCM

Not saying this is necessarily the case here, but I've seen similar problems involving files where the header information indicates one sample rate, yet the file was actually recorded at a different rate.  The file then plays back at the incorrect rate indicated in it's header, which changes it's run time.  Just a possibility to be aware of. 

You might try adjusting the playback rate of the shorter file down to 44.1.  Actually you'd probably do it the other way around- indicate to the software that the file rate of the longer file is 44.1 but have it play back as a 48kHz file, and see if that syncs closer.

But that's mostly an academic exercise if you still need to strech one to match the other anyway.  You might as well just stretch it, as long as the non-linearities within the stretch points are acceptable.  Maybe the practical thing is to simply determine how long you can go before needing new sync points.
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Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<< (note: This is a 1st draft, now several years old and in need of revision!  Stay tuned)

Offline Teen Wolf Blitzer

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Re: A/V sync problems
« Reply #14 on: December 23, 2013, 10:12:21 AM »
2 words..  Plurel Eyes.  Get it.   ;D

Offline beatkilla

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Re: A/V sync problems
« Reply #15 on: December 23, 2013, 10:39:55 AM »
2 words..  Plurel Eyes.  Get it.   ;D

Last i checked plural eyes did only synch at one point and not take into account for drift has this changed now?

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Re: A/V sync problems
« Reply #16 on: December 23, 2013, 10:55:48 AM »
2 words..  Plurel Eyes.  Get it.   ;D

Last i checked plural eyes did only synch at one point and not take into account for drift has this changed now?
same wih fcp I believe
I just got fpcx recently and when I used the built in synch/mutli mix it was on at the beginning but not the end
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Offline yousef

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Re: A/V sync problems
« Reply #17 on: December 23, 2013, 11:35:48 AM »
Last i checked plural eyes did only synch at one point and not take into account for drift has this changed now?

Really??? I just assumed it was one-stop solution. That's a shame - finding a single sync point seems to be easy enough, it's the stretching and checking that sync is maintained that takes all the time...

I guess you could just chop all your video clips into 10min chunks and let Plural Eyes sync them up to work around this.
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runonce

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Re: A/V sync problems
« Reply #18 on: December 23, 2013, 02:11:31 PM »
Last i checked plural eyes did only synch at one point and not take into account for drift has this changed now?

Really??? I just assumed it was one-stop solution. That's a shame - finding a single sync point seems to be easy enough, it's the stretching and checking that sync is maintained that takes all the time...

I guess you could just chop all your video clips into 10min chunks and let Plural Eyes sync them up to work around this.

I think  the problem with the "chop and sync" is - you are syncing 2 sources that aren't in tune with each other...(if drift is the issue)

Offline yousef

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Re: A/V sync problems
« Reply #19 on: December 23, 2013, 02:14:45 PM »
I think  the problem with the "chop and sync" is - you are syncing 2 sources that aren't in tune with each other...(if drift is the issue)

But I generally only have one audio track running in the final video - I use the audio from each cam as a means to sync and then mute all but the separately recorded audio when everything is lined up.
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runonce

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Re: A/V sync problems
« Reply #20 on: December 23, 2013, 02:31:22 PM »
I think  the problem with the "chop and sync" is - you are syncing 2 sources that aren't in tune with each other...(if drift is the issue)

But I generally only have one audio track running in the final video - I use the audio from each cam as a means to sync and then mute all but the separately recorded audio when everything is lined up.

Ah...10-4

Offline Gutbucket

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Re: A/V sync problems
« Reply #21 on: December 23, 2013, 03:32:32 PM »
I think  the problem with the "chop and sync" is - you are syncing 2 sources that aren't in tune with each other...(if drift is the issue)

But I generally only have one audio track running in the final video - I use the audio from each cam as a means to sync and then mute all but the separately recorded audio when everything is lined up.

In that case any minor non-linearities which remain between the files after one global sync-stretch (not chopping, but just stretching/shrinking the full length file) shouldn't be of consequence.  Using the video from one source and the audio from the other, you only need the sources synced closely enough to eliminate visible 'lip-sync' problems, rather than needing to get them close enough to avoid phase-related problems when mixing the two audio sources.  The first has a far greater tollerance for mismatch than the second.
« Last Edit: December 23, 2013, 03:38:42 PM by Gutbucket »
musical volition > vibrations > voltages > numeric values > voltages > vibrations> virtual teleportation time-machine experience
Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<< (note: This is a 1st draft, now several years old and in need of revision!  Stay tuned)

Offline yousef

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Re: A/V sync problems
« Reply #22 on: December 23, 2013, 03:46:35 PM »
In that case any minor non-linearities which remain between the files after one global sync-stretch (not chopping, but just stretching/shrinking the full length file) shouldn't be of consequence.  Using the video from one source and the audio from the other, you only need the sources synced closely enough to eliminate visible 'lip-sync' problems, rather than needing to get them close enough to avoid phase-related problems when mixing the two audio sources.  The first has a far greater tollerance for mismatch than the second.

This is true - and reflects my usual workflow. Having said that, the idea of chopping the video into chunks and letting a program line them all up does sound tempting when compared to some of the trickier experiences I've had when trying to stretch files.
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Offline techgui

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Re: A/V sync problems
« Reply #23 on: December 23, 2013, 05:13:23 PM »
OK, I put everything back on the time line today, synced the start points and found that after 47 minutes, the drift is 82ms not 3.4 seconds.  Still large enough to hear two distinct clicks, but nowhere as bad as I originally thought.  Don't know how I screwed up the original numbers. 

Just received my PluralEyes software.  Works great.  I just threw the (3) camcorders and the board audio into vegas and let PluralEyes sync everything up.  Then I went back and used Crtl/drag to adjust the end of the soundboard audio to sync with camera 1. 
« Last Edit: December 26, 2013, 08:24:32 AM by techgui »

 

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