How can I do color keying using the VSE?

Question

I've been playing around with the VSE a lot lately and I was wondering about its tools-- the strip effects-- and what you can do with them. One effect I want to pull off in the VSE is color keying, is there any conceivable way to do this? If I could pull off green screen effects with just strip modifiers and strip effects, it would solve most, if not all of my problems.

I edited together a 3 minute long video with a handful of static shots in front of a green screen, I rendered it out and figured it would be easiest to take care of all at once in the compositor but I also thought input nodes could be animated to accommodate a new background for each shot. That is the real problem I'm trying to solve if the VSE green screen doesn't work out.

Great thanks in advance to anyone who helps out here.

Answer 1

Option 1

The VSE cannot do a chroma key by itself. You can however make a simple key with modifiers. In this example I have:

1. The foreground strip (source A) at the bottom to serve as key source
2. Then I slightly blur it to hide imperfect edges

3. The yellow color effect serves as background
4. Duplicate the foreground source clip to the top (source B)
5. Add a Mask Modifier to it using strip Blur as its input

6. To source A add a Hue Correct modifier and set its Value and increase key colour (blue or green) range to all other colours to 0 . Use the curve to tune colours in or out of key. Switch to the S button for saturation and edit the curve so that all Control Points are at 0 or black and white.
7. Add Curve modifier to source A. Raise the black control point (bottom left to the top and lower the white point control point (top right) to the bottom. Place an extra control point in the middle and drag it right up to the top making a high contrast key image.

Remember to press the refresh Sequencer button while you do these changes to see the result.

Option 2:

Otherwise use the compositor. It has proper keying nodes. You can add your source clip as an input to a compositor in another scene (this is important). Perform the key there but don't add a background, make sure to use the Convert Alpha node to premultiply the output. In the VSE add that scene (with the compositor active) as a scene strip, make sure to use Alpha Over. Then place and trim as you wish over the background strip in the VSE.