That's it the cookie cutter. How do I define the cut out area for the effects to use? How do I get the effect ot recognise the defined area or am I just just being thick?

Thanks for the reply by the way.

The cookie cutter is limited to a few basic shapes such as rectangles, ovals, triangles, etc. but you can stretch and move these around and fade the edges. You can often get something to fit pretty close to the area you want.

In order to combine the cookie cutter with an effect you have to use two tracks. Place identical copies of the video clip on both tracks, synchronised one right above the other. Place the effect on the lower clip and the cookie cutter on the upper clip. Set the cookie cutter to cut away section. You'll now see the unaffected version from the top clip covering most of the frame and the effected version from the lower track in the cut out section.

If you need custom shapes you can always create your own as a black-on-white still image using any photo editor or drawing program. You can then use this still as a custom mask.