Thanks for the feature request. The trickiest part is getting both videos to synchronize, and making sure the performance is acceptable. I'll have to do some research and testing to see if it's feasible. Packing the alpha into the same video is much easier and probably more performant, since only one video needs to be decoded. You can also create an hsp file with the correct alpha mask settings and distribute it with the video, and the correct settings will automatically be loaded when the user plays the video.

Hi!

sorry for spamming this post but I can't seem to get my alpha-packed passthrough video to work :( 
From what I understand, I'm supposed to composite an original video with the alpha matte video into the same "canvas" and shift the coordinates to let heresphere know which part of the canvas to sample to produce the transparency?

I have a 3840 x 1920 Equirectangular 180 SBS video composited with a 3840 x 1920 Equirectangular 180 SBS  video matte in a side-by-side configuration ( so it's now 7680 x 1920, aspect ratio of 4 ) and my settings are:

Shift X -0.5, Shift Y 0, Scale X 1.0, Scale Y 1.0

but it shows up a little bit funky, the subject is split down the middle on the left and right side of the viewing space while in Equirectangular 180 FOV;  switching to Equirectangular 360 kinda fixes that but only the left-eye frame is matting properly, the right-eye frame is somehow matting with what looks like an inverted film negative version of the original video 

here's the video (NSFW) 
https://mega.nz/file/InBlAC6Z#Vg92yvA6o1J0AJPGr9-mIfkfFleLGOJTa_-T-x2lbK8

Please let me know if there are any examples I should follow to get it working!

Thanks for the help! :)