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Fixing inaccurate camera sync

User avatar sammuirhead
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Fixing inaccurate camera sync

Tue Dec 15, 2015 10:41 am
One of a series of posts dealing with issues I encountered when trying to edit a long and complex documentary with Kdenlive - the problems I outline cost a lot of time, and require repetitive manual tasks where new features and shortcuts in the software could do the job better.
Other posts:
Independent length adjustment of synched audio.
Export for Sound Mix

Fixing inaccurate camera sync

The Problem:
I shot most of the documentary with the Canon 5D Mk II, a 7-year old camera. Magic Lantern helps a lot, but there are still a few little issues - one is that sound is usually 1.5-2 frames out of sync with the video. Many other cameras have similar issues.
This is a related, though not identical issue to my post on Independent length adjustment of synched audio.

Current Workaround:
To fix this, I would normally do:
Right Click>Split Audio
Right Click>Ungroup Clips
Click on Audio clip
Place cursor at the Start/End of the clip and zoom in (so I can see how many frames I'm moving it)
Drag audio two frames into position with the mouse

Sometimes I would Group the A+V clips again, but I find the Group function so buggy and inconsistent that I'm scared of it and tend to avoid it.
But now the video clip has no audio information which I can use to check the sync difference, or grab other nearby audio later. And if a bunch of the timeline gets knocked out of sync (that damn spacer tool selectively moving certain tracks!) then I have no reference to line it back up to its original position anymore, and have to hunt for the right spot manually.

So I add a couple of extra steps to this workflow:
1. Copy Video clip (includes audio)
2. Paste it somewhere nearby.
3. (on the pasted clip) Right Click>Split Audio
4. Right Click>Ungroup Clips
5. Delete pasted Video
6. Drag audio into line with original clip
7. Place cursor at the Start/End of the clip and zoom in (so I can see how many frames I'm moving it)
8. Drag audio two frames into synched position with the mouse

This is of course a dumb and insanely inefficient workaround, but it retains the audio information with the video clip.

Potential Solutions: (not necessarily all to be used together)
- 'Offset Audio' effect, where I could select a bunch of clips in the timeline or in the bin, or a track in the timeline, and set an audio offset of two frames for all of them. Then the clip can be used as normal, and there's some little visual +2 tag on the clip in the timeline which informs me of the shift.

- 'Shift selection' option - when I have a (A or V) clip selected, there should be an option where I can hold down a modifier key and use the L+R arrow keys to shift it one frame, or the PgUp/PgDwn keys to shift it 10 frames. It would save a lot of unnecessary clicking.

- 'Roll/Slip selection' option - proprietary NLEs have the option to keep a clip's start and end points in their existing position in the timeline, while either sliding the content of the clip forwards or backwards with the mouse, or shifting it frame-by-frame with a keyboard shortcut.

- 'Right Click>Restore Audio' option for Video clips which no longer have associated audio.

- 'Show Clip in original File' - 'Show Clip in Project Bin' is useful, but it only shows me the whole file, not the exact spot within that file, or the subclip which it corresponds to. I would like to be taken to the actual In and Out points of this particular clip I have selected in the timeline. That way I can happily split audio in the timeline, knowing that I have a safety net in that I can always get the audio back from the original.

- 'Match Frame' functionality, familiar to anyone who has worked with proprietary NLEs, would also be useful. This is like 'Show Clip in Original File' except it also positions the playhead in the Clip Monitor at the exact frame it is positioned in the timeline.

Other Ideas?
Is this a problem for other people?
Does anybody have suggestions for other current workarounds?
Thoughts on how potential solutions might be able to be implemented in Kdenlive?
Other relevant or related bugs/problems?


http://www.cameralibre.cc
Free Culture videos made with Free/Libre/Open Source Software about Open Hardware, Open Data, Open Everything

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