I just took the rotobrush tool for a spin and my mind was blown. Such an amazing, effective tool, feels magical. Major props to Adobe.
Anyway, I tried using it to take the background out of a .jpg, then I dragged the .jpg into a composition to animate around. I noticed, however, that when I tried to do a preview of the animation I'd created, part way through the image regains its background. What have I done to make it do this/how do I keep the background from coming back? I tried re-reading about working with the rotobrush, but I couldn't catch this.
I'm such an idiot, I didn't drag out the slider under the roto work. Solved.