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Time Stretch = Jumpy Footage

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Mitch LewisTime Stretch = Jumpy Footage
by on May 28, 2010 at 9:59:19 pm

I'm a long time After Effects user, but I've never run into this problem before....

I'm producing a 30-second tv commercial. There are 6 different scenes and each scene is it's own comp. Those 6 comps are then nested into a final 30 second comp. Each of the 6 individual comps contain a spokesperson shot in green screen and some b-roll video floating beside her. The green screen footage is 30p where as the b-roll footage is 60i. I don't think that contributes to the problem I'm having though.

It starts with the fact that the spokesperson's lines add up to more than 30-seconds. So as a fix, I sped up each of the 6 nested comps to 94% using Time Stretch. (I plan to correct the chipmunk sounding audio later using dedicated audio software).

The problem is that when I render out the final 30-second comp and play it back in Quicktime Player, about every 2 seconds or so, the video "jumps". It looks like it's skipping a couple frames or something. It plays smoothly then skips, then plays smoothly then skips. I tried turning on Frame Blending (high quality) inside the individual comps and re-rendering, but the problem still remains.

I think it has something to do with speeding up the individual comps. But I can't figure out exactly what the issue is. Can any one provide some suggestions?

Thanks in advance.


---------------------------
Sony EX3, Canon 5DM2, Sachtler tripod - 20+ years as a videographer/editor
Experienced with Apple products, Final Cut Studio, Adobe Creative Suite, MOTU Digital Performer, Flip4Mac, etc...


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Mitch LewisRe: Time Stretch = Jumpy Footage
by on May 28, 2010 at 10:05:14 pm

Here's some sample video from the project I'm having problems with.

http://vimeo.com/12121085

---------------------------
Sony EX3, Canon 5DM2, Sachtler tripod - 20+ years as a videographer/editor
Experienced with Apple products, Final Cut Studio, Adobe Creative Suite, MOTU Digital Performer, Flip4Mac, etc...


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Dave LaRondeRe: Time Stretch = Jumpy Footage
by on May 28, 2010 at 10:55:42 pm

Ouch. Speeding up video by a fraction like that pretty much guarantees goofy motion. Rather than doing that, I'd be tempted to cut out a portion of one of the talent's lines.

The alternative: do the speedup in hardware at a post house. It'll look fine, but it won't be cheap. Look for a gizmo called a Terranex box.

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


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Mitch LewisRe: Time Stretch = Jumpy Footage
by on May 28, 2010 at 11:00:22 pm

No kidding? I guess I have used AE to slow down footage frequently and just assumed that speeding it up would look the same. But yeah, you're right, normally I slow down footage to 200% (1/2 speed). 94% is a small fraction of a change.

Hmmm...... I need to figure out a different solution. Thanks!

---------------------------
Sony EX3, Canon 5DM2, Sachtler tripod - 20+ years as a videographer/editor
Experienced with Apple products, Final Cut Studio, Adobe Creative Suite, MOTU Digital Performer, Flip4Mac, etc...


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Dave LaRondeRe: Time Stretch = Jumpy Footage
by on May 28, 2010 at 11:05:27 pm

[Mitch Lewis] "Hmmm...... I need to figure out a different solution. "

Yup. Ain't it hell when you run long? But I bet if you go back and look at all the takes, you can cut together a spot that comes in under :30.

I always do that BEFORE I take the footage into AE.

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


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Jim ArcoRe: Time Stretch = Jumpy Footage
by on May 29, 2010 at 12:10:18 pm

Time-stretch by small amounts seems to work strangely in AE. I have had some luck by first time-warping the video to 200% or 400%, then time-stretch the result (in another comp) by the appropriate amount to get to the speed I need. Make sure pixel-motion is on and add motion shutter blur if needed.

This gives AE more frames to work with and would change your time-stretch to a larger amount, 47% or 23.4% for instance. Time-warp can be messy with interlaced footage, so you might have to do some other work there.



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Jim ArcoRe: Time Stretch = Jumpy Footage
by on May 29, 2010 at 12:18:53 pm

Forgot to mention:

The technique I listed was from an idea provided to me by Chris Wright when I was looking for a better method for frame rate conversions for Super8 film.


Jim


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Jim ArcoCorrection: Time Stretch = Jumpy Footage
by on May 29, 2010 at 12:42:04 pm

Well, I hadn't had my first coffee yet...

With time-warp you want to get more frames to work with / slow the video down. So... you need to time-warp to 50% or 25%, then time-stretch by the same amount.


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Mitch LewisRe: Correction: Time Stretch = Jumpy Footage
by on May 29, 2010 at 2:55:18 pm

Thanks Dave and Jjm. Jim - that's a very interesting idea. But I ended up doing what Dave said. I found an area where the spokesperson wasn't looking at the camera which allowed me to edit her audio and not worry about lip-sync (because you can't see her lips). That allowed me to negate using Time Stretch on any of the footage but still get her audio down to 29:15 seconds. I'm happy.

Thanks again. :)

---------------------------
Sony EX3, Canon 5DM2, Sachtler tripod - 20+ years as a videographer/editor
Experienced with Apple products, Final Cut Studio, Adobe Creative Suite, MOTU Digital Performer, Flip4Mac, etc...


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