Depending on how much movement your shot has, will determin how much work will go into this. Again, if someone knows a better way to do this, please speak up….
I’d have 2 layers of the same video, the bottom layer I would apply what ever blur filter I wanted, and the top layer I would apply a mask to. The mask would make the bottom layer visible, while keeping your main subject in tack. Now if you have lots of movements, there’s going to be a great deal of keying involved, but that’s where the “Record” button comes in handy with Motion.
I use a very similar work flow when in FCP, because we don’t have some of the nicer plug-in’s that allow you to have only one layer of video (which keeps your renders faster).
Hope this helps in down the right path. 🙂
“If God could do the tricks we can do, He’d be a happy Man.” – Peter O’Toole – “The Stuntman”
Machine Model: Power Mac G5
CPU Type: PowerPC G5 (3.0)
Number Of CPUs: 2
CPU Speed: 2.5 GHz
L2 Cache (per CPU): 512 KB
Memory: 4.5 GB
Final Cut Studio (Not Universal, yet)