Track one face, apply the tracking info to a null object, add another tracker, and repeat.
When you click to track the footage a second time, it should create a second tracker. However, if it doesn’t, you’ve already got your tracking info from the first track saved on your null.
Track as many faces as you need to then use your favorite blur technique using the nulls as your track point info.
One way to do it would be to precomp all those moving nulls, add little feathered shape layers into the precomp (the same size as the faces – see where I’m going with this?), parent them to the nulls, and then use that precomp as a track matte for a blur adjustment layer.
– The Great Szalam
(The ‘Great’ stands for ‘Not So Great, in fact, Extremely Humble’)
No trees were harmed in the creation of this message, but several thousand electrons were mildly inconvenienced.