Mike Ross

I am trying to blend multiple overlapping videos together without blending them into the background. Ultimately the behavior I am going for is that wherever N videos overlap, the resulting pixels are an average of each of the N source pixels. So wherever there is just one video, it should be the pixels from that video without blending with the background. Right now I have the background set to Red, but I would like to ultimately make it a jpg. There will eventually be multiple videos which are moving on screen so their overlapping portions will be constantly changing.

So far I have the test patch below, in which the videos are blending into the background. The idea is that the videos should blend where they overlap, but they should not appear red-tinted. I tried to blend to a jit.gl.node, and then set the node to @color 1. 1. 1. 1. -- but this just passes the 1.0 alpha back up to the source videos so it ruins the initial blend.

I am also questioning whether using jit.gl.videoplane @blend is the right approach. I might be wrong about this. But based on the documentation, it sounds like it wont actually be an average of N videos. Instead, if I have 10 videos with alpha 0.5, then the result will be a 50% blend of the 10-th video with the results of the previous 9 put together. I would prefer a result with 10% of the blend coming from each video so that the order of the layers does not matter.

So far I have the test patch below, in which the videos are blending into the background. The idea is that the videos should blend where they overlap, but they should not appear red-tinted. I tried to blend to a jit.gl.node, and then set the node to @color 1. 1. 1. 1.  -- but this just passes the 1.0 alpha back up to the source videos so it ruins the initial blend.

I am also questioning whether using jit.gl.videoplane @blend is the right approach.  I might be wrong about this. But based on the documentation, it sounds like it wont actually be an average of N videos. Instead, if I have 10 videos with alpha 0.5, then the result will be a 50% blend of the 10-th video with the results of the previous 9 put together. I would prefer a result with 10% of the blend coming from each video so that the order of the layers does not matter.

blend-videos-without-blending-into-background

you have to set the bottom most layer using the @layer attribute and disable blending on that layer using @blend_enable 0:

Thanks so much for your reply. But that patch doesn't quite do what I am looking for. I am trying to have the movies blend with each other (where they overlap), but totally obscure the red background without blending with it. In your patch, it looks like one of the videos will always blend with the background.

I attached a still jpg showing what behavior I am going for.

Eventually instead of a red background, I might want a background video or jpg that does not blend with any of the foreground movies (the foreground movies would still blend with each other). So maybe the background should be a separate video pane? But I still can't get the behavior I am looking for.

third videoplane behind the other two layers with blending disabled, lined up with the layer that has blending enabled:

Ok thanks. This looks like the outcome I am going for. If I am understanding correctly, this solution requires 2*N videoplanes for N videos. I tried to generalize to 3 and it appears to be working. But am I losing efficiency by having 6 videoplanes to show 3 videos? See here:

efficiency gains will be made by removing the pwindows and enabling texture output with jit.movie @output_texture 1

Blend videos without blending into background