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Background moving in slower framerate than foreground?


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Hey guys! Trying to pull off a practical effect where the lead singer in a band I'm shooting is lipsyncing the song at normal speed, while things in the backgronud (ie. bottle being throwing against a wall and smashing) happen in slo-motion. Is it really as simple as just having the lead singer sing the song twice as fast and film in 48fps? Thanks!

Edited by Eric Gesualdo
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If you want things like bottle smashes to be really slow and awesome looking 48fps might not cut it. 

Slowmo starts too look cool in the 150 to 200 fps bracket for thinks breaking if you want to see the particles clearly. 

The other problem with the performer learning to lip sync at high speed means her motion will look strange as well - they will look slowed down as well, even with lip sync and a 2X speed up as David said is really hard to do. 4x or 6x to get more slow mo even more impossible. 

The other approach would be shoot it in two passes. Lock the camera off and shoot the background action in slow mo.

Then shoot the shot again at normal speed with the singer in position. You could use a portable green screen to comp the two together or use  the roto brush in after effects to cut round the singer so you can comp him on the slow background. You could shoot the singer in green screen in a studio but its easier on location to match the lighting. 

In terms of light levels you'd want to put ND in for the normal speed, rather then stopping down - so both show happen at the same f stop. 

 

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19 hours ago, Phil Connolly said:

If you want things like bottle smashes to be really slow and awesome looking 48fps might not cut it. 

Slowmo starts too look cool in the 150 to 200 fps bracket for thinks breaking if you want to see the particles clearly. 

The other problem with the performer learning to lip sync at high speed means her motion will look strange as well - they will look slowed down as well, even with lip sync and a 2X speed up as David said is really hard to do. 4x or 6x to get more slow mo even more impossible. 

The other approach would be shoot it in two passes. Lock the camera off and shoot the background action in slow mo.

Then shoot the shot again at normal speed with the singer in position. You could use a portable green screen to comp the two together or use  the roto brush in after effects to cut round the singer so you can comp him on the slow background. You could shoot the singer in green screen in a studio but its easier on location to match the lighting. 

In terms of light levels you'd want to put ND in for the normal speed, rather then stopping down - so both show happen at the same f stop. 

 

Thank you for your thoughtful response! This helped immensely. 

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I've done the opposite.  Background in fast motion, foreground in normal speed.

We did this by lighting the foreground and background, removing the foreground actors and furniture, shooting the background as a plate, and then bringing in a green screen to shoot the foreground against and composited in post.  It worked quite well.

Ours was complicated by the requirement that the lighting change from day to night during the shot, and this required that the lighting changes be designed into the setup in advance...

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