Step 1: Duplicate the video you want to pixelate on an upper track. (You should have the same video on both tracks) Step 2: Add the Pixelate Video FX to the upper track. (the whole upper video should be pixilated). Step 3: Add the Cookie Cutter Video FX to the upper track. Step 4: Select the Preset: Circle Center. Make sure the Method is Cut away all but selection. Step 5: Adjust the Size to fit the area you want to pixelate and move it to the area you want cover.
That’s it.
If the face moves in the video you will need to use the Begin and End keyframes to move the cookie cutter. If you need more keyframes, you need to cut the clips to get more begin and end points.
Actually, I just used JohnnyRoy's instructions VERBATIM (from an earlier post) to do a "COPS" style pixelation on some brief nudity in a piece I worked on last night and it worked perfectly!