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Workflow for Retiming Tracked Content (open discussion)

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jay ingles
Workflow for Retiming Tracked Content (open discussion)
on Aug 27, 2011 at 6:41:45 am

I'm working on "phone demo" videos (think iPhone commercial) that need to be retimed to work with the voice-over and screens animated/replaced. I've tracked one of the videos/screens (and shape layers for hand gestures) in Mocha and have reimported into After Effects.

How can i keep the precomp'd screens customizable and not get lost in keyframes from the tracked content?


Approach #1: Time-remap video & screens together
Problem: The video content on the screens wouldn't be playing at a proper frame rate.

Approach #2: time-remap the master clip in advance, then Track in Mocha.
Problem: Not customizable. (ie: if client asks to extend one area of the video)

***Approach #3:*** somehow timeremap "main video" precomp, but still have "screen" play back at proper frame rate and properly tracked.

Looking for insight.
Thanks!


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ben g unguren
Re: Workflow for Retiming Tracked Content (open discussion)
on Aug 27, 2011 at 2:25:07 pm

The third approach works IF the footage isn't being slowed down, but only sped up. The reason for this is because the tracked footage is kept in place with keyframes, which can interpolate halfway-between positions, whereas the base plate of images doesn't have anything to interpolate:

With SLOWED IMAGE FRAMES, some of them will repeat:
1, 2, 2, 3, 4, 4, 5, 6, 6, 7, 8, 8

With SLOWED KEYFRAME TRACKING DATA, there is interpolation:
1, 1.6, 2.3, 3, 3.6, 4.3, 5, 5.6, 6.3, 7, 7.6, 8.3

We often don't notice the jumpiness of the slowed image frames, but they will become terribly jittery if we superimpose a smooth-moving something-or-other on top of it:

1.0, 1.6, 2.3, 3.0, 3.6, 4.3, 5.0, 5.6
1.0, 2.0, 2.0, 3.0, 4.0, 4.0, 5.0, 6.0

I've tried using TimeWarp to adjust the image, but there isn't nearly enough precision in most cases to match things up properly. You could perhaps change all your tracking keyframes to hold keyframes, which would therefore refuse to interpolate and match the image, but then you'd lose any motion-blur capabilities.


If you're only speeding up, then things should (should!) line up. The trick is getting the keyframes to match the remap. This is pretty straightforward, actually. Here's how I do it:

Time Remap your base layer -- let's name it "MainPlate_Remapped". If you have more than one instance of your base layer going (as a procedural matte, or maybe masking some foreground elements) then apply Time Remapping and use the pick whip to give it this expression:

thisComp.layer("MainPlate_Remapped").timeRemap)

Now it will correspond with your base remapped layer.


For anything else with motion-matching keyframes (which is probably most of the keyframes) you add the following expression:

value_at_time(thisComp.layer("MainPlate_Remapped").timeRemap)

This simple bit of code causes the layer to sample the keyframed values relative to where the time remapped layer is currently looking. So the movements should all match up. (This assumes all your clips start at 0 in the timeline. If they don't you need to precomp things so they do, or add an offset value to your value_at_time expression.)

Once this is all set up you can slide the footage that's being inserted around all you want, independent of the time remapping of the base footage and tracking keyframes.

Ben Unguren
Motion Graphics & Editing
http://www.mostlydocumentary.com


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jay ingles
Re: Workflow for Retiming Tracked Content (open discussion)
on Aug 27, 2011 at 2:36:05 pm

Thanks Ben, that's great insight.

I was considering using expressions to match the remap, but anticipate some undesireable last minute issues.

I'm starting to feel more confident about locking down on some variables and precomposing the screen+video together and time-remapping that as a whole.

Not my ideal approach but i think may be the fastest solution.

Do you have any insight or problems i may be overlooking?
Thanks!


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Tudor "Ted" Jelescu
Re: Workflow for Retiming Tracked Content (open discussion)
on Aug 27, 2011 at 2:28:43 pm

I had a similar issue. What I did was to workout the animation with track data on footage as it was, precomp and then time remap the precomp. I set keyframes for events on the audio track and then worked between the animations inside the precomp and the time remap to make all fit. One thing my client was made aware of was that once he approved the audio there was no going back and changing it without extra budget.

Tudor "Ted" Jelescu
Senior VFX Artist


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jay ingles
Re: Workflow for Retiming Tracked Content (open discussion)
on Aug 27, 2011 at 2:32:21 pm

Thanks guys.

Ted, would you advise this method over time remapping the Main video to time, then render out and use Mocha to track. Followed by bringing back into AE and adding the screens in?

Of course this locks the edit to the VO, but at least then there isn't hte potential issue of keyframe tracking going wrong.

What do you think, Should i lock down some variables?


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Dave LaRonde
Re: Workflow for Retiming Tracked Content (open discussion)
on Aug 27, 2011 at 3:44:37 pm

Clients love to have all their options open until the very end. Effects people like to have everything nailed down at the very beginning to save time and money for the client.

To me, this appears to come down to that old adage of TV production: "You can have it good, you can have it fast, you can have it cheap. Pick any two."

It's time for the client to face reality, and I think it's time for you to explain reality to the client.

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


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jay ingles
Re: Workflow for Retiming Tracked Content (open discussion)
on Aug 27, 2011 at 6:07:40 pm

Hahah, thanks Dave. And yes i've explained the limitations in a high level fashion to the agency. I'm just firming up on the technical possibilities.

I've decided to retime the base/parent video and track from that. Then screens are still editable for content but not for timing.

Thanks everyone for chiming in.
Appreciated.


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Tudor "Ted" Jelescu
Re: Workflow for Retiming Tracked Content (open discussion)
on Aug 27, 2011 at 4:54:59 pm

It's hard to say not really knowing the footage you work with and the kind of animations you need to produce. The workflow I described gave me just enough flexibility to be able to change animations and match them to the audio track. Usually I either ask my clients to lock the audio and tweak the animation later OR to lock the animation and then record the audio on the finished animation. It's hard to tweak both without compromise.

Tudor "Ted" Jelescu
Senior VFX Artist


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