You do not need 2 tracks.
1 track using mask simple shape, mosaic, mask apply. Replace mosaic with blur if you want to.
To move the blur, key frame the H and V positions of the mask to follow the movement. Not easy, but doable.
You do not need 2 tracks.
1 track using mask simple shape, mosaic, mask apply. Replace mosaic with blur if you want to.
To move the blur, key frame the H and V positions of the mask to follow the movement. Not easy, but doable.