Combine fast and normal speed in the same clip?

A

alekstef

Well-known member
Hello!

I want to film a scene with a girl standing in the middle and people walking past her, both in front of her and behind her. The people have to move fast, like a time lapse, but the girl has to move in normal speed.

I don't know how to do this.. Bluescreen?

What I have disposable:

Sony PD-170
Panasonic DVX-100
I can maybe barrow a Sony Betacam SX camera...
Bluescreen
FCS 2
AE CS3

Anyone who knows how to do this?
 
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I think you guys misunderstood me. I know how to speed up and speed down a clip. What I want is ONE person who moves in NORMAL motion, while the rest of them move in fast motion :) So how do I do this? I've searched for a while now, but couldn't find anything spesific.
 
the lo-tech approach would be to fake the person moving at 'normal speed' by having them move really slowly while everyone else moves normally then speeding up the clip playback. But that depends a lot on what the non-standard-speed person is supposed to be doing - I'd forget it if she's supposed to be talking or walking or anything else where timing is critical.

A more flexible approach would be greenscreen - film your crowd all moving around a small marker obstacle, then film the one person against a greenscreen, and composite her into the space where the obstacle was, with different speeds on the playbacks
 
Thank you! What do you mean with a small marker obstacle? A green object that I replace with the greenscreen-person?
 
ideally, something that will be hidden by the later composite layer on top, could be something as simple as a pole a bit shorter than the person. Or even something out of shot like a box or a big 'don't stand here' red marker on the ground. Depends also on how close the passers-by are supposed to get to the (virtual) person. Whatever method you use, you're just trying to avoid the passers-by walking 'through' the position of the person, otherwise it will look weird when the person is composited in front.

I'm presuming here that none of the passers-by need to walk in front of the person - that would add a whole extra pile of problems
 
Hm.. I did want people to walk in front of the person, but I guess it is not necessary... Thank you :) It helped a lot.

Edit: How would it be if i wanted to dolly around the person....?
 
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I recently worked on some P.S.A.s where we filmed our backgrounds of people walking fast and composited a normal speed person in front of them. We also shot a crowd of people moving fast in front of a large greenscreen for the foreground. I think the final shots looked great, and it was relatively easy to accomplish, but there was no camera movement. Adding camera movement would increase the difficulty exponentially.

To dolly around a person, you would need a motion control rig for the camera, and you would have to calculate the speed of your background and foreground people and slow down the speed of the motion control rig accordingly.
 
yeah, unless you have a whole lot of time/money/equipment, you definitely want to do this as a static camera shot.

as mentioned above, you can have people moving in front of the person too, so long as you're happy to film them against a greenscreen and composite them in as an extra front layer. It very much depends on the relative direction the passers-by are moving in. But do everything you can to avoid the same passer-by moving behind and in front of the person, that's just nasty to do.

The general rule for low-budget greenscreen is to minimise the number of layers - every extra layer increases the chance of doing something wrong and ending up with an unconvincing composite.
 
The more camera movement you incorporate the more difficult it will be to assemble the shot. A static shot will definitely be the easiest way to go.

As for people passing in front of your normal speed person, that shouldn't be an issue..

Here's what I would do:

Shoot your plate.. the "fast moving people" with something in the position the normal speed person will be so they don't occupy that space.

Shoot your normal speed person on a greenscreen at the same distance/camera height, angle, etc.

Import your footage, remap the time on your plate footage.

Pull the key from your GS footage, and place it on a layer above the plate, then use mattes as needed to obscure your GS person if/when someone crosses in front of them. It will take a bit extra time in post, but it will also help sell the shot, because someone could then walk from behind your normal person, around the side, and cross in front rather than having all the people who cross in front come from off screen.
 
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