I have a .mov clip in After Effects and I am trying to use the Roto Brush tool on a foreground object. On the first stroke, the segmentation boundary selects the entire frame instead of the foreground object. My questions are: Why does that happen and what to do to fix it?
Without any idea about your footage nobody can tell you much. Some scenarios simply don't work that well with RB due to its internal logic. If cleaning up the selected regions by subtracting strokes doesn't work, then chances are slim that it will ever work in the way you possibly want it to.
Plus, we don't know if you're making Rotobrush mistakes. It's not an intuitive too, you know.
Did you ever solve your Rotobrush issue? Please let us know what happened or if you still need help.