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TOPIC: Problem Synchronizing audio and video

Problem Synchronizing audio and video 26 Apr 2016 17:55 #76085

Hi,

I was recording a 1-1/2 hour panel discussion using two cameras - GH4 with Sennheiser MKE-400 hotshoe mic, and GX8 with inbuilt mic. The panelists had lav mics and their voices were broadcast on speakers on either side of the room. I recorded the audio via a mixer using a Tascam DR-40WL and imported the WAV file to FCP X 10.2.3. The audio on the Tascam was great as the event location had a large audio setup and I just plugged into XLR out and the audiotech adjusted lav mic levels.

For some reason the first 12 minutes sync properly then sporadic syncing on different clips since GH4 breaks up files in 4gb chunks. I attempted to sync each 4gb clip to the master audio file recordby by DR-40WL but not having much luck. Just wondering why the first 12 minutes synced up. The audio recorded by the GH4/GX8 is a little low and tinny but I can make out what they are saying.

I have about 8 clips that need to be synced from the two cameras. Any idea how to do this quicker than lining up audio track to video tracks? Thanks.
Last Edit: 26 Apr 2016 17:57 by filterstuck.
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Problem Synchronizing audio and video 26 Apr 2016 18:31 #76086

  • joema
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The most important step is making sure the clips from each device are labeled in the FCPX metadata (either camera angle or camera name). Below is the camera name procedure, which should include your Tascam audio files. Maybe you already did this but I include it just in case:

1. Import all clips
2. In Event Browser at top left select List View (it's the button above the red X at left)
3. In Event Browser, click on clip name to sort by name. All the clips from each camera should be grouped together.
4. Select a group of clips from one camera/recorder (Click on 1st, go to last and Shift-click).
5. In Inspector at upper right, click on Info button. If Inspector pane is not on, turn it on with Window>Show Inspector
6. At bottom of Inspector Pane, click the drop-down box and select "General". This shows more details.
7. In the Inspector Pane, enter a camera name. When you press Enter it will add that camera name to all the clips you have selected in a single step.
8. Repeat step 4 and 7 for each camera/recorder.
9. In Event Browser, select all clips from all the cameras you added camera name info to.
10. Right-click on the selected group and select "New Multicam Clip", then set checkbox "use audio for synchronization"

Given camera angle or camera name, FCPX does a halfway decent job of syncing by audio. I have sync'd about 40 clips successfully, provided the audio is really good. OTOH I've had cases where the sync fails with 5 clips. Even worse it doesn't give a "can't sync" error it just gives its best shot and places the clips somewhere. If you don't check the sync of each clip you never know if it was successful.

While convenient and built in, it is not remotely as capable as PluralEyes, so if FCPX won't do the trick that is another option. The latest version of PluralEyes 4.0 can automatically detect different cameras and assign them to unique bins: www.redgiant.com/products/pluraleyes/ It also automatically handles sync drift if one camera runs faster than another on a long take. Its audio analysis algorithm is apparently much more sophisticated than FCPX.
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Problem Synchronizing audio and video 26 Apr 2016 18:33 #76087

I synchronized the video clips individually to the master audio but there seems to be an issue with synchronized clip preview as I was only getting black bars and no video showing on the synchronized clip timeline. I scrubbed through the area where the tracks synced and discovered some of the video had synced but there was still no video on parts of the clips.

I have 6 sequential clips named GH4-20160422-1008 to 1013. Camera was not moved and all clips just need to sync to one audio file recorded on Tascam.

Video goes black on certain parts of the beginning and end of each synchronized clip making it impossible to join the clips together. Here is an example of black video around synchronized audio:

imgur.com/7X3fbTb

is there a bulletproof method of syncing audio to video clips that might be broken up in 4gb chunks? If I stop the cameras, audio sync doesn't seem to work on clips where the camera started up again.

I think the issue is with the GH4 splitting the file at 4gb. Didn't think this would be hard for FCPX to do. I'm not sure why some audio syncs to the video and other doesn't.
Last Edit: 26 Apr 2016 18:48 by filterstuck.
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Problem Synchronizing audio and video 26 Apr 2016 19:35 #76090

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filterstuck wrote:
...Here is an example of black video around synchronized audio...
is there a bulletproof method of syncing audio to video clips that might be broken up in 4gb chunks? If I stop the cameras, audio sync doesn't seem to work on clips where the camera started up again...

That showed black thumbnails; that by itself doesn't mean the video track was black. Did you open the project in the Angle Editor and inspect what the sync looked like? If there are black video regions, what does each video track look like at that point in the Angle Editor?

With any sync algorithm there is a possible conflict when using multiple clips per camera (which you usually have). Consider two A/V clips, 1 and 2, and a continuous audio track. If A/V clip 1 is incorrectly synced to the audio track, then it tries to since A/V clip 2, even if that sync is successful it might create an overlap with clip 1. It won't truncate a clip so it just moves clip 2 somewhere else, maybe its 2nd best guess (which is wrong). Thus a single sync failure on one clip can throw off the sync of other clips.

Unfortunately there is no way to override the algorithm or provide a priority. You can use markers which helps when syncing by audio but it requires approximate manual positioning of the markers.

In the Angle Editor if you can identify which clip was incorrectly synced, you can possibly remove that from the multicam sequence and re-sync without it. Then you can possibly add the "difficult" clip manually. Or sometimes you can just "touch up" the sync in the Angle Editor by moving an improperly-synced clip left/right to bring it in sync.

If you have any really short clips where the camera only ran a few seconds, it's usually best to exclude those from the sync, as a single "difficult" clip can throw everything off.

I usually make a quick attempt to sync it in FCPX and if that doesn't work just use PluralEyes.
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Problem Synchronizing audio and video 27 Apr 2016 05:59 #76099

Joema,

Thanks. I think I figured it out through trial and error. It was a combination of what you stated. The black areas did contain some video when I scrubbed through them but not at the beginning and ends. The video clip was also black in the areas where there was no syncing of the video. So this combination of not showing areas of synced video on the clip preview was confusing.
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