I am making a FMV game, so I want to use video encryption prevent player directly play it in media player. I have checked godot PCK do support encryption, I may use it instead of video encryption.
I think the extra bytes of alpha channels should not cause that big impact. I have try to make a video + alpha mask side by side (because I want to use av1 codec but it don't support alpha) and use a modified shader play the alpha channel video without any speed problem.