[PD] pix_multiblob cpu usage

I made a 400x300 motion JPEG-a movie 15 fps with 5 solid blue circles moving on a black background to test pix_mutiblob. I open it up with pix_film, flip it with pix_flip and send it to pix_multiblob. I suddenly notices PD getting very, very slow. When I look at the cpu usage in activity monitor (if you can believe activity monitor) I get 100-104% cpu usage. I cant do anything else in PD because PD gets so slow. I am using a dual 2Ghz G5 with ATI Radeon 9800 XT and 3GB of internal memory. Is this normal? What can I do to lower cpu usage? What else can I use within Gem to get the same results? I eventually want to be able to track 20-30 objects but It looks like it would be imposible at this rate. Thanks, Alain