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linking rotation of video to ae camera
hey all
i’ve just watched a behind the scenes video on the belief site for their zoom tv package. in it they shot a girl against green screen rotating on the spot. he mentioned they were able to write a simple expression linking the movement of the girl to the camera in after effects. any idea how this would work or where i could find this expression?
thanks for your help ahead of time!
brad goosen -
6 Replies
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Unless I missed something, there isn’t anything to magical about the linking of the shot to a camera move. You would not extract a rotation value directly from the footage. What could be done is an inference of rotation based on time. If the turntable is a constant speed and it takes 4 seconds to go 360 degrees then you can set this change in rotation to the camera and the back ground would appear to move at the same rate. This could be used to give the impression that the camera dolled around the talent in the space.
I’m not sure why you would even create an expression but if you wanted to you would look at the number of frames in the turntable shot and determain a ratio between the rotation and the time (i.e. 360/(4*framerate)). I’m sure Dan Eberts could help with the expession itself.TonyTony
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If I saw the video probably that would help, but as I understand what you say… They probably tracked the rotation of the girl with two trackers (front and behind? left and right shoulders? must see the video) into a null object and then attached the camera to it.
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hey
yeah thanks for the help…
the clip can be found here
https://tinyurl.com/s56n8
just press view movie and it will show you the behind the scenes video… its an element for part 3.
yeah i guess averaging the movement based on rotation makes sense… but i guess its my natural instinct to want to make things harder than they should be!
thanks
brad -
No need for tracking.
Position A is at time q,
Position A is returned to at time p,
Time of rotation is q-p = r
Camera rotation time = r
So long as the girl on the turn-table is rotated at a constant speed you got no problems.Now if you wanted to make it seem as if you dolled around in a natural setting you would have to setup a light rig that would show what the light would look like on the girl from all the different angles and have smooth transitions.
TonyTony
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Yep, you were right. I just thought it was shot from the top and the movement was irregular (that would make a curious effect by the way)
If the movement is (almost) constant, you just have to play with the rotation value until you get it right, it’s easy to make even if you don’t know the original rotation speed.
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thanks for your help… as always the cow comes through!
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