Required: optional for video clips
Range: positive floating point number
Determines playback speed of video clips. Values less than one speed the video up, while values greater than one slow it down.
A clip's duration before triming is equal to its speed attribute times its media's length attribute.
freezeend: boolean - zero (false) or one (true)
freezestart: boolean - zero (false) or one (true)
id: any alphanumeric string
length: integer (units of mash quatization)
speed: positive floating point number
start: floating point number
trimend: integer (units of mash quatization)
trimstart: integer (units of mash quatization)
volume: comma delimited floats from 0 to 100