Why does my transparent footage background have a black screen?

Question

PROBLEM

Hi, I'm using Blender 2.93. I have some video footage I exported with DaVinci Resolve. It has has an alpha channel. When I load it back into DV, it shows it truly has an alpha channel because I can put anything under it, and it acts as you'd expect: like a PNG with transparency in areas I want, but in video form.

Then when I load it into Blender as an image sequence: Add -> Image -> Images As Planes, and make sure the Use alpha and Auto refresh are both on... The video imports with a black background where it should be transparent, but the rest of the video is fine.

WHAT I'VE TREID

• Everything I said above.
• The images as planes docs
• This thread with a similar problem, though with PNG's. Not working either.
• Exporting the alpha with premultiply and straight.
• Ian Hubert's YouTube video. And oddly, none of my video's icons are transparent as his are... Mine show black where they should be transparent, even though the transparency works in DV.
• This youtube video showing his footage having no black screen.
• Going to Properties -> Render properties -> Film -> Transparent on.
• In the Shading tab, the alpha output of the video is connected to the alpha of the Pirncipled BSDF.

I'm wondering if this is some video codec issue?? The video is a .mov file with a DNxHR 444 12-bit codec, which Blender might be incompatible with?

Any ideas?

Answer 1

The issue was a codec issue. In DV I exported with a GoPro CineForm codec RGB-16 bit, and it worked. I read the available codecs in the blender docs, and that one isn't even listed there, but I bet it's probably using one of the others listed, probably open source or something.

UPDATE 2022: if anyone comes across this problem too in Cycles, make sure you turn up the max bounces in Render Properties -> Light Paths -> Max bounces -> Transparent, or else you will still get a black background. Adjust Total bounces accordingly too, in the same area.