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Invert Time Remapping on Another Layer

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Dan Turner
Invert Time Remapping on Another Layer
on Jul 26, 2016 at 8:59:45 pm

Hi all, so I'm trying to do something a bit unusual.

I've got an audio layer, and a video layer above it.

The video layer has Time Remapping applied, and I need to find a way to take that information and use it to stretch the audio in the opposite direction.

Ie, the clip has a ramp (explained in velocity) 100 - 300 - 100, I then need to do the inverse to the audio: 100 - 33.33 - 100.
But involving ramps etc, complicated keyframing.

The reason being is that I'm doing a pre-vis, and I need to record visuals that will sync when remapped with the original track.

Any advice on this much appreciated, hoping there's a quick way or an expression that will do the job.


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Dan Turner
Re: Invert Time Remapping on Another Layer
on Jul 26, 2016 at 10:47:40 pm

Just explain this a little further

The top track is the Time Remapped video track, with the audio underneath:

Expanded graph:

I need to effectively stretch the audio out so if that time remapping was applied to it, it would playback at regular speed, if that makes sense...

I can imagine there may be a way to do it with pre-composing things and applying an expression, but my little brain can't think how it may work...


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Jerry Smith
Re: Invert Time Remapping on Another Layer
on Jul 27, 2016 at 1:41:47 am

You basically need to invert a function. But keyframing in general isn't invertible. In math lingo, the keyframing function isn't 1-1. You can map many points to one. That happens less often with time-remapping than other properties perhaps and it doesn't seem to be the case in your graph. But, I don't think AE has any easy way to invert even some section of keyframing. Now, if you could somehow make all your keyframing linear, then it might be easier. But time remapping, unlike position, doesn't allow very accurate parameterization, ie no subframe positioning. So, you'll have to do a bunch of extra number crunching to get the inverted numbers on the frame boundaries. Ugh.

But I'm just a pleb. Maybe one of the patricians actually has something elegant for you. Good luck.

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Dan Turner
Re: Invert Time Remapping on Another Layer
on Jul 27, 2016 at 6:08:25 am

Hi Jerry, thanks for the reply - I thought this may be the case, as the pesky nature of how time works means there's essentially a logic problem as well, but that's a separate issue to what you're describing.

Hopefully someone can help out!

In the meantime I've experimented with a crude workaround - convert all frames to linear, add correlating TR keyframes on the audio track, and pull both out in the graph editor until velocity is 1/1 on the video track... it's not pretty and it destroys all the elegance of the curves however

Good luck me, help me guardian angels!

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