The displace effect uses a video, image or theme media item as a displacement map
for the underlying video and effect tracks. It's used to create many distortion
filters like wave, ripple, glass and more.
Displacement maps work by moving each pixel in the underlying video by an amount
that's based on the transparency of the same pixel in the displace visual.
For instance, a video of concentric circles radiating outwards will
approximate a ripple filter when used as a map.
editable: comma delimited list of property names
id: single word string identifier, starting with a letter
length: floating point number (frames)
composites: valid video or image media id
scale: comma delimited percentage values
symbol: a valid SWF URL, followed by an ampersand and class name
type: the string 'effect'