Forgot to say what I'm working with now--do I need a new computer or just some upgrades?
Intel Core i7 - 3820 CPU @ 3.60GHz
32 GB RAM
64-bit operating system
ATI Radeon HD 5570
What 64 bit operating system? What kind of footage? Have you gone through the tutorials and the FAQ about Rotobrush? Do you know now to set span? What version of AE right down to the last decimal point?
I have no clue what may be causing this problem. It could be anything from the codec used in the original footage to the size of the footage, to the available ram, to your memory settings, to an out of date version of AE.
Windows 7 pro
footage in 1920 1080 AVCHD but mainly I need to work in 600x600 FLV
Yes I know how to set span and it goes really really really slow when I'm trying to see how the shot looks in one frame that is in the span
After Effects CC 18.104.22.168
AVCHD isn't a really good type of footage to use: AE has to do a lot of looking backward & forward to reconstruct the video current frame.
As a test, transcode one of your clips to.... oh, say, a quicktime movie in Photo JPEG codec a lossless Windows codec and see if it speeds up Rotobrush for you.