How do I make a new file that will not have to be rendered again?

Question

This is a little complicated but I've tried everything and still can't find a solution.
Here's what I'm doing:
1. Record footage with my Canon HV 30 in 1080 30p mode.
2. I import it into Final Cut Studio 6. Plays back fine.
3. I add chroma key and garbage matts to get rid of green screen. Now it has to be rendered to play back at all.
4. So, I'm trying to make a new movie out of the footage with the chroma key so that I can then import it and play it back without having to render every time a move something.
I know it has to be exported in the same format as the FC file in order to do this, but when I do that I don't get an alpha channel so the places where the green screen was is now black instead of see through.
I tried saving in animation and "no compression" with the alpha channel but then it won't play back without the rendering again.
Am I asking to do the impossible?
Thanks. And I'm sort of new to this so please keep it simple.

Answer 1

Hey there, wireduck! There are two ways to render out keyed footage.
If you export to animation codec (choose millions of colors + ),
I believe you need to export from an UNrendered FCP sequence.
So make sure your sequence has the little red or orange lines, then export.
This should produce a file with a good alpha channel.
The problem is that the animation codec is big and processor-intensive,
as is your other HDV footage. So it might work, but you'll get bogged down
at some future point.
A cool trick is to convert the entire sequence to the DVCPRO HD codec.
It's really easy for your computer to digest, and it looks great.
Now here's the trick to export the alpha channel as a separate file.
On your keyed clip, after the other effects (color smoothing, key),
add the Channel Swap filter, and set red, blue, and green from alpha.
By doing this, you are making the RGB channels display your alpha channel.
Export this (DVCPRO HD) and name it the same as your clip,
but with something like "-alpha" at the end so you can keep track of it.
Import it.
In your sequence (sequence settings DVCPRO HD, yes?), place the original
footage--with all the keying and channel effects disabled--on V3.
Set its Composite Mode to Travel Matte - Luma.
Directly below that, on V2, perfectly aligned to the original clip,
place your -alpha clip with normal composite mode.
Now put your background on V1.
You should see the composite working, and three tracks of DVCPRO HD
should play on your computer OK without needing to render.
Just keep the original clip (on V3) and its alpha version (on V2)
perfectly in sync, and you can edit and add other effects.
This should work for you. Good luck!