Your patch works for me with depth_enable 0. Note that we don't want to clip based on depth testing (as demonstrated in the jit.gl.videoplane-xfade.pat example). Using depth testing (which is on by default) will only render one video plane in your patch since the video planes are both at the same distance from the camera.

The other thing worth noting is that right to left order is not maintained necessarily with send recieve, so the other possibility is that your left movie (which looks like the one you are assuming to have alpha) renders first, and that the right movie renders second (with no alpha, overlaying over the image). You will want to use either two instances of send/receive (as demonstrated in jit.gl.videoplane-example.pat) or use one receive with trigger to force sequencing.

Lastly, you'll want to turn automatic off as demonstrated in as demonstrated in jit.gl.videoplane-example.pat.

-Joshua