I have a comp that I brought in via XML from FCP and it references the full video file. I wanted to render the footage in FCP as a different type of file to use in AE but I don't want to lose all my work with the rotobrush. Is there a way, maybe keep timecode and reference in AE, to copy or move the rotobrush selection to the new footage? Thanks
Since it is based on analysing the real pixel data, there is no way to just copy&paste it to a new layer and get the exact same result. Of course you can do that with the strokes, which act like any other normal paint stroke, but the analysis result may be different. I therefore recommend you at least render out the result you have now as a matte or footage with Alpha channel so you can use it as a starting point and work incrementally from there (pre-compose the matte with the new layer using a matte mode) or as reference at least. Only then try that copy&paste stuff.
Old topic, but with no answer, so here it is
Just use FREEZE button and than you can just copy/paste. Same goes for moving rotobrush project to another project (especially in case of AE versions mismatch)