applying basic chroma key in Avid

[sean90291]

So, it's the first time I've tried a keying out a "green screen." But something ain't right.

I imported HDV footage (from an HV20) into a 1080i/59.94 project. (Actually I had to capture it using HDV Split and then import into Avid, but that's another story.)

Then I put my background on V1 and my green screen footage on V2. I apply the chroma key effect to V2 and it "keys out" the green perfectly, with very little tweaking at all. That is, the green screen goes BLACK. The rest of the image is the same and the green screen area is totally blackened. I assume that the black equals transparent. But when I put my background on V1, it doesn't show through. I still have a black green screen, as though it's not transparent at all...just black. I'm missing a step, obviously. But I can't figure out what it is.

Going to Avid Help didn't help. It does suggest that there is an "opacity" parameter, and maybe I have to reduce the opacity somehow. But I don't even see an opacity parameter in my Effect Editor for ChromaKey. Hm. I'm stumped already.

 

[cbrougham]

Check that "Render on the fly" is enabled. I'm not sitting in front of an Avid right now, but it's a menu option. Maybe under "Clip" or "Bin"? If that doesn't work, check your options in the key effect. You should be able to reverse the matte, swap sources, view just the matte channel, and a couple other things. Just flip a few toggles in there, and see if that doesn't help... but after you check for "render on the fly".

 

[grinner]

are you using spectrakey?
I have never found a use for Avid's regualar chroma key. Just too primative.

 

[sean90291]

Aha! I figured out what was wrong. The background has to be on V1! That means it has to be on the real ORIGINAL V1 track. Not a track that was V2 and then I moved down to be the lowest video track. Apparently re-ordering track layers on an Avid timeline just re-orders how you VIEW them, not how they're ordered in terms of rendering. Similarly, re-naming a V2 track as V1 does not make it the "V1" track. I'd like to know how to truly move tracks up or down, because Ctrl+dragging a timeline just changes the viewing of the layer, not how it functions with effects relying on the order of video track layers.

So I got the key to work by starting a new timeline and not moving any video layers: just keeping background on the original V1 and the foreground on the original V2 and not moving them!

 

[milksac]

I'd like to know how to truly move tracks up or down, because Ctrl+dragging a timeline just changes the viewing of the layer, not how it functions with effects relying on the order of video track layers.

Moving the order of tracks around is confusing for the editor as you've discovered. Leave the tracks in their default position. You want to move the clips not the tracks. To move the clips around use segment mode, it's in the help menu (sorry, I don't feel like typing it all out today). In segment mode your cursor turns into a red or yellow arrow and it allows the editor to grab clips and move them around on the timeline.

 

[sean90291]

Thanks. I use the segment mode all the time. It's just a bit clunky for moving "tracks" when you're used to After Effects. Because with segment mode, if you want to switch the order of an upper level/lower level track you have to go through a few extra steps in Avid. Anyhow, good to know I wasn't missing out on some great technique. I'll just use segment mode!