Comment 4 for bug 1650372

I need it inside the 3D scene.

My use case: I'm creating a 360°-video-like player, cubic using six faces, similar to a skybox. Each face plays a high resolution video. Around the cube can be another cube, again with video-textures on its faces. To be able to see through the next cube, the foreground videos will have (semi-)transparent areas via their alpha channel.