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Time Stretching and Precomps

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Ryan Hill
Time Stretching and Precomps
on Aug 14, 2012 at 11:26:15 pm

I've had this crop up a couple times recently. I'll have stabilized footage or an animated mask or something, and then I want to time-reverse or time-stretch or time-remap it. So I pre-comp it, moving all the animated masks and motion into the pre-comp, and then change the timing on the pre-comp.

But then, the stabilized footage gets shaky again, or the animated mask doesn't match up anymore. I guess what's happening is it's using the between-frame values for those animated elements.

Is there any sort of setting I can change to make it treat the frames of the pre-comp as indivisible?



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Dave LaRonde
Re: Time Stretching and Precomps
on Aug 15, 2012 at 3:36:16 pm

I know this is more time-consuming, but in a case like this I'd prerender the comp in question. Then the sync of the original work is preserved.

You can't really expect to time remap or time stretch to your heart's desire. There are limits to what you can do with non-still-frame footage like video before things get weird.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Ryan Hill
Re: Time Stretching and Precomps
on Aug 15, 2012 at 7:14:31 pm

I was kind of hoping there was some sort of hidden check-box I could tick that said, "Treat this comp as though it were pre-rendered."

I'll give the examples that inspired the question. I did resort to pre-rendering in these cases, but I was wondering if there was another way:

Suppose I had a stop-motion sequence I wanted to composite into some video footage, and I spent a bunch of time masking out the feet for a clean key before realizing I had let it interpret the stop-motion as 30fps when the video is 24fps?

Suppose I had a Super 8 transfer that was pretty shaky, so I stabilized it based on the sprocket hole, only to realize one piece of footage in the middle had been spliced in backwards, so it's upside-down and time-reversed?



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Dave LaRonde
Re: Time Stretching and Precomps
on Aug 15, 2012 at 8:01:42 pm

[Ryan Hill] "Suppose I had a stop-motion sequence I wanted to composite into some video footage, and I spent a bunch of time masking out the feet for a clean key before realizing I had let it interpret the stop-motion as 30fps when the video is 24fps?"

Start over. No fooling. We all make Homer Simpson-style "Doh!" mistakes, and the more painful they are, the less freauently we make them.



[Ryan Hill] "Suppose I had a Super 8 transfer that was pretty shaky, so I stabilized it based on the sprocket hole, only to realize one piece of footage in the middle had been spliced in backwards, so it's upside-down and time-reversed?"

Render the footage losslessly. Import into AE. Put into a comp. Find the first fame of bad footage and use the Split Layer function. Find the first frame of good footage after it and split the layer. You now have the bad footage isolated. Time Stretch or Time Remap it to run backwards, and turn it upside down any number of ways. The bad video now runs properly.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Chris Nielsen
Re: Time Stretching and Precomps
on Mar 31, 2014 at 3:42:22 am

I realize this is an old topic but I've recently had one of those.... hair pulling moments of frustration.

Anyhow, my workflow always requires multiple levels of revisions, so prerenders don't quite cut it for me. What I've found to solve this issue is rather simple - setting all keyframes to HOLD.

Of course this could open a whole new can of worms for you depending on what exactly you're stretching, but it's always a handy trick for the back pocket. Thinking about what the software is doing - basically remapping the time between keyframes - it's going to assume you want the tweens to operate in kind. Hold keyframes preempt this.


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