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tracking speed to control frame rate

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Daniel Cantwell
tracking speed to control frame rate
on Apr 25, 2019 at 2:38:23 pm

Howdy Folks

I was wondering does anybody have any experience controlling frame rate with the speed curve of tracking data. I am sure it should be possible to have a linear camera move rendered out at a high frame rate (provided the distance rendered is the same as a live action camera) and have the speed of a live action track control the frame rate to get the appropriate ease in and out. Any help with this would be greatly appreciated.


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Dave LaRonde
Re: tracking speed to control frame rate
on Apr 25, 2019 at 10:46:57 pm

To clarify things........ well, a LOT, could you please describe what you're trying to accomplish.

What are you tracking? Why do you feel this track is crucial to controlling frame rate?

I haven't heard of anyone doing this, and I suspect there's an easier way to get the job done besides what you're thinking.

Dave LaRonde
Promotion Producer
KGAN (CBS) & KFXA (Fox) Cedar Rapids, IA


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Daniel Cantwell
Re: tracking speed to control frame rate
on Apr 26, 2019 at 2:44:03 am

Hi Dave

Thanks for your reply. I have two sources.

1. A live action plate of a subject walking left to right with tracking markers. The track is 28 feet.

2. A scale model at 1-18 scale. The camera is motion controlled, so it can shoot at very precise intervals giving a linear camera move with no ramp up or down in speed and a heavy overlap of frames over the move, say 800 frames. The camera is a stills camera. The distance from the live action can be divided by 18 giving the scale model length so the distance is correct. I am looking for a way to control the frame rate of the 800 frames with the speed curve of the track to give the correct ramp up and down in speed given the distance is accurate.

Yes there are a lot of other ways of doing this. For instance the BG could be stitched and the various BG assets could be put on 2.5d planes with a virtual camera giving parallax or the BG could be photogrammetry and again a virtual camera used. Really this is just to satisfy my curiosity it could be done with an expression. Theoretically it seems like it should be possible.

All the best


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Kalleheikki Kannisto
Re: tracking speed to control frame rate
on Apr 26, 2019 at 6:39:13 am

What I would try is this theory:

- The regular speed is in the middle of the pan. This would be a specific time remapping speed, let's say this is S.
- At the regular speed the tracking markers move X pixels per frame.
- Now you know that X pixels per frame equals S time remapping speed.
- When the motion stops, the time remapping speed is 0, and the tracking speed is 0.
- The question is whether the in-between values are linear or not. I assume they are.

Based on that theory you only need to know what S and X are in the middle of the pan and linearly interpolate the S values from the X values. Apply that to the speed value of time remapping. I don't have AE open, so I don't remember if the built-in time remapping can be done by speed, but at least Twixtor can do so.

Kalleheikki Kannisto
Senior Graphic Designer


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Walter Soyka
Re: tracking speed to control frame rate
on Apr 26, 2019 at 10:19:38 am

I think that if you can apply the tracking data to a null that goes from the start of the track to its finish, and you can identify the times in the clip that correspond to those positions, you should just be able to remap that X position data to the time-remapping duration linearly -- no need to ever calculate the speed. Variation in the tracking speed will then be interpolated proportionally across the frame rate.

So if we know the initial X position is -1000 and the final X position is 1000, and if we know those positions in the corresponding clip are at 2.0 seconds and end at 37.5 seconds, we could enable time-remapping for the layer and apply this expression:

linear(XPOS, -1000, 1000, 2, 37.5);

Just replace XPOS with a reference to the null's X position.

Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive [twitter]   |   RenderBreak [blog]   |   Profile [LinkedIn]


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Daniel Cantwell
Re: tracking speed to control frame rate
on Apr 26, 2019 at 4:18:12 pm

Thanks everyone for your suggestions. Walter, you sir, are a legend! Worked a treat! All the best and many thanks.


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Kalleheikki Kannisto
Re: tracking speed to control frame rate
on Apr 27, 2019 at 11:28:55 am

It would seem this exacerbates the problem by adding extra offset the rather than evening it out. Any offset in position from a linear motion would add the corresponding amount of time remapping offset rather than removing it. At least that's what my brain says.

Kalleheikki Kannisto
Senior Graphic Designer


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Walter Soyka
Re: tracking speed to control frame rate
on Apr 29, 2019 at 3:10:09 pm

As I understand the challenge here, we have a tracked foreground element that moves in X only, and a constant, linear X move on a background that we need to match to the tracked foreground element.

Since the background move is linear and constant, X movement and time are the same thing. We can use time-remapping as a proxy for X position, and a linear interpolation between the two extremes should stick to the track.

Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive [twitter]   |   RenderBreak [blog]   |   Profile [LinkedIn]


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Kalleheikki Kannisto
Re: tracking speed to control frame rate
on Apr 30, 2019 at 8:42:39 am

I guess the long and the short of it is, if it works, it works!

Kalleheikki Kannisto
Senior Graphic Designer


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