Automate mask feather based on mask movement

[Redsandro]

I was wondering if someone already made something like this.
Rotoscoping motionblurred footage is not the easiest in After Effects. It would be good if there's an expression that takes all the points on a mask, and compares them temporally spatially (the positions to the previous or next frame), generating a value between 0 and 1 where 1 is a lot of difference (and 0 is ofcourse none).

Then you could have a feathered value of say 4 + 20 * theValue.

[Paul Tuersley]

In my experience, rotoscoping motion blurred footage is very easy in After Effects. Just turn on motion blur for the layer and you're done. Am I missing something?

[Redsandro]

Motion blur only works for moving layers.
I mean feathering (not motion-blurring) the right amount for the motion tracked mask to match the motionblur of the footage (the motion blur that is already there), which would obviously increase when the mask moves more (and not the footage so the motion blur option does nothing).

[Paul Tuersley]

Motion blur works on animated masks regardless of whether the layer is moving.

[Redsandro]

Maybe I should feel stupid now.. CS3?
I'll check it out later..

[Redsandro]

What the hell? This is awesome! This is exactly what I want, but better! (Ofcourse after changing blur samples in composition settings to 8+.)
I sooo didn't know this.
Thanks!

[Redsandro]

Now a lot of other animating masks that were perfect mess up the layer though.
I think I know the answer, but I recently learned I am wrong sometimes. But can motion blur be disabled for certain masks only?

[Paul Tuersley]

Yes. Select a mask then choose Layer > Mask > Motion Blur > Same As Layer/ On / Off.

[Redsandro]

OMG, AE is awesome!
Thanks.

Adobe should have put a feature movie on that video DVD that came with though. I like watching movies but the manual is written too explicitly to read 'just for fun'.