Spike Jonze "Undone" effect, timing help.

[JoeFowler]

I was asked by a friend to make a music video for their local band which has been playing two to three shows a week. I wanted to try a few things, one of them is to do the effect that Spike did for the Weezer Undone (The Sweater Song) video.

In the video, they played the song faster then normal, and had the band play to that speed. Then slowed the footage down so that it plays normal speed, but the video looks slow motion. Cool effect, but here's my question:

What's the formula? How fast should I make the song, to then slow down to match the song at regular speed?

Like, if I speed the song up 20%, do I slow the footage down 20% to match it up again?

Or am I doing the math wrong. What is your experience?

If you are confused by what I'm asking let me know, and I'll try to explain it better.

Thanks!

[CaptainMench]

You are correct

CaptM

[JoeFowler]

Ok, thanks Capt.

But... In Final Cut, I take the song in and modify speed to 120, which makes the song play faster, (and the duration shorter)...

Then after I get the footage shot with the faster song, I then modify speed to 80?

This is where the confusion is, for me.

[bigbossbmb]

no, you can't just +20 and then -20 later...it is just a ratio between video speed and audio speed.

if you want the video to play back at 1/2 (50 in FCP) speed, then you must record them performing at 2x (or 200 in FCP) speed. If you are only slowing the video to say 3/4 speed (75 in FCP)...then you need to speed up the audio for shooting to 1.33x speed.

Shooting Video Speed/Shooting Audio Speed = Playback Video Speed/Playback Audio Speed

But since shooting video speed and playback audio speed are both 100%, the formula works out to:
Playback Video Speed x Shooting Audio Speed = 1

To use FCP numbers, divde by 100 for each (ie 50/100=.5 or 1/2 speed)

[gunleik]

% math... -;)

You have 100 + 20% = 120

the "new" 100% = 120 (FCP @ 100)


to find back too 100 you have to,
(120/100)*x=100
1,2*x=100
X=100/1,2
X=83,333
(replace 100 + x% with any desired number...)

You would make it easier on yourself to speed up to 125% and then go to 80%

Or. If you're on an HVX you'll be best off finding a speed that corresponds to one of the overcrank speeds and adjust correspondingly. That way you can avoid frame-blending.


Gunleik