Rotobrush rendering starts off fast, then gets slower, then 1 frame per 10 seconds... then hangs.

[Letty2019]

Very frustrated.

I have a real simple clip, 30 seconds of a wall, camera almost still, all I did was mask out one mirror.  The wall is blank, one color.

Very simple mask.

So I mask out the square mirror, using Rotobrush 2.0  (the mirror has small crooked borders, didn't want the pen tool, RB 2.0 is better).   

I do notice there is a lot of fluctuation in the RB 2.0 in the border of the mirror.  The mirror border has a great deal of small jaggy edges so I'm assuming it's slow because it can't find a pattern?  But it starts rendering just fine then slows down.

Then I render it, starts off at about 2 frames per second.  Nice.   Then slowly goes to about 1 frame per second.  livable.  then, gets slower and slower, to the point of hanging.  shot has no effects is a clean .mov file  1080p.  Feels like it's running out of gas.  It goes thru about half the clip before dragging, then pooping out.   

RB 1.0 is horrible.  Can't stay still.  I guess it's back to the dreaded pen tool and lots of feathering.

my system:  32gb, ss drives, gtx 1050 ti,  Ryzen 7. 

I don't think throwing money at this problem is a solution. (buying an overpriced gpu card)  

Please send me your thoughts. 

Thank you!!

Letty

[Mylenium · Accepted solution]

You pretty much answered your own question: RB thrives on detectable changing patterns to synthesize the underlying motion field. No motion, not change in the field, no threshold calculations to draw the border. And with RB 2.0 it gets even worse because it tries to be too smart for its own good and attempts to fix the lack of actual patterns by throwing endless calculations from the AI algorithms at it. Going back to conventional masks seems sensible, though perhaps there may be ways to extract a clean matte using other means. Having a reference frame/ screenshot might help to make a determination on that...

Mylenium

[Letty2019]

You seem to be spot on.

When I do RB with cleaner images, it works like a charm, but throw some moving jagged borders in the mix, and it's hell.

Pen tool to the rescue. 

With all the new AI stuff coming out, I'll bet AE makes a great AI rotobrush 3.0 , but, I know they come out with it AFTER I finish my film.

Thanks for your prior thoughts.

Letty