I created a video sequence in Bleder’s VIdeo Sequence Editor and now I want to use it as a background for the camera (my intent is to composite a 3d scene on top of it).
Is this possible or do I have to render my video sequence and THEN use it for compositing?
I don’t think you can use a VSE output in the viewport. I think you’re gonna have to render it out.
You could map the movie onto a plane that is parented to the camera, depending on how complex your camera movements are (i.e. changing focal lengthwill look weird)
I strongly suggest that you approach this as “a compositing problem.” Personally, I would do it using several blend-files.
(1) First, generate the video background, as though nothing were superimposed upon it. (I presume you’ve already got this.)
(1a) If, in your show, this background isn’t “a flat backdrop,” then create another blend-file which, taking the video from step #1 as input, produces a new version that can have the output of step #2 superimposed upon it.
(2) Now, separately, generate the 3D content … without a background, with a black world-color, and in a file-format that supports RGBA. When you look at this file, the characters are performing surrounded by absolute, alpha=0.0, blackness. (Probably, they’re anti-aliased.)
(3) Finally, use VSE or another video-editor to “alpha-over” the 3D content onto the video background. The files generated in steps #1 and #2 are used as inputs.