Weird alpha behavior on video

Hey everyone, I’m having some doubts regarding how touchdesigner handles alpha in video files. I have a quicktime footage rendered with animation codec with alpha. When I load it into TD, it shows up like this:

No big deal, I just go to the Image tab in the operator’s properties and set it to mutiply color by alpha, which gives me:

Great, problem solved, until I decide to build a feedback loop with the video:

The only way I could solve this was adding a glsl top right after the movie file in, and have it multiplying the color by the alpha, again!

That pretty much solves the issue, but not really. As you can see, the footage keeps a weird white outline at the edge of the alpha. Also, it only works with both the “multiply color by alpha” option set to on and the glsl multiplication. If I remove any of them, the white background shows up again.

For referece, this is how it looks in after effects if I go for the same effect, stacking a bunch of layers and resizing them to simulate the feedback I built in TD. As you can see, the alpha is clear, with no white outline.

Any thoughts or ideas on why it works like that, and if there’s any workaround?

Thanks!

Any chance your input footage is sRGB?

You could also use the display pixel values toggle to see what the value of your alpha channel really is, that might help you narrow down what’s happening there.

Thanks for the suggestions. Setting the input to sRGB left the image really dark, but didn’t change the alpha issues.

When I inspect the pixel values, the only thing I get is that my alpha is never really 0, which makes sense if you look into the after effects screenshot above, in which you can see there’s a kind of “fog” in the footage. Actually, it’s even weirder that I can’t see this fog in TD. It kinda gives me the impression that the feedback loop has an additive like blend going on, which makes this fog go white instead of darker, and may also bring up this white outline. Does it make any sense?