I received one of my very short clips edited from Unscreen website (which removes background of the vid) but they sent me the mp4 of the video (with the background) and an alpha file which I have no idea how to work with on blender (neither on any other software anyway!) I want to import my video with a transparent background and apparently I have to mix somehow the mp4 and the alpha file.

Does anyone can tell me a simple procedure to do so on VSE?

Thanks in advance



1 Answer 1


As mp4 doesn't support alpha channel, the file you have is a black and white movie that brings the alpha information.

White means matte, while black means transparent.

In Blender compositor (or any other) you can plug it into a color mix node, where black will bring the top input image, white the bottom input.

In VSE you can add a mask modifier to the video strip that needs transparency, targeting the alpha strip.

Alpha strip has to stay under the visible strips.

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  • $\begingroup$ I tried... it is working...tank you so much Josh $\endgroup$ May 6, 2021 at 12:26
  • $\begingroup$ I still had trouble because I had to cut my mp4 into 4 pieces and it was lagging. So I made a proxy, then referenced each part to each alpha created automaticaly, but some parts were lagging like hell...did not manage to render perfectly $\endgroup$ May 6, 2021 at 19:03
  • $\begingroup$ Blender VSE is far from perfection, use free version of DaVinci Resolve instead, where theese tasks are fairly easy. $\endgroup$ May 7, 2021 at 6:53
  • $\begingroup$ yeah, I think I am going to do this...fed up to spend days to try to make that thing work...and it is still not working...Blender is probably very good for animation $\endgroup$ May 8, 2021 at 12:31

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