How to put animated background to keyed video?

Question

I keyed out a video because it had grass and put in an animated background. How do I get the keying to work?

Before background with keying:

Now with animated background:

What am I doing wrong? Thanks!

It looks like the keying node is not generating a properly associated alpha channel. Try enabling "convert to premultiply" https://i.stack.imgur.com/hidAQ.png — no-can-do, Oct 13 '20 at 07:59
Please write an answer to your own question, so that others with similar issues can learn form you. — no-can-do, Oct 13 '20 at 21:01

score 1 · Answer 1 · answered Nov 05 '20 at 16:46

1

Enable "convert to premultiply" to show the top video/image over video/image.

answered Nov 05 '20 at 16:46

Sandy

59
4

score 1 · Answer 2 · answered Dec 10 '20 at 21:47

This has been fixed on blender version 2.92 You no longer need to set the alpha to premultiply.

As explained here: https://developer.blender.org/rBf68c3d557aa

Compositor: Ensure keying node result is pre-multiplied

Historically the result of the keying node was violating alpha pre-multiplication rules in Blender: it was simply overriding the alpha channel of input.

This change makes it so keying node mixes alpha into the input, which solves the following issues:

The result is properly pre-multiplied, no need in separate alpha-convert node anymore. Allows to more easily stack keying nodes. This usecase was never really investigated, but since previously alpha is always overwritten it was never possible to easily stack nodes. Now it is at something to be tried. Unfortunately, this breaks compatibility with existing files, where alpha-convert node is to be manually removed.

How to put animated background to keyed video?

2 Answers2

Linked