Returns the lengthof a frame for this AVItem, in seconds. This is the reciprocal of frameRate. When set, the reciprocal is automatically set as a new frameRate value.
This attribute returns the reciprocal of the frameRate, which may not be identical to a value you set, if that value is not evenly divisible into 1.0 (for example, 0.3). Due to numerical limitations, (1 / (1 / 0.3)) is close to, but not exactly, 0.3.
If the AVItem is a FootageItem, this value is linked to the mainSource, and is read-only. To change it, set the conformFrameRate of the mainSource object. This sets both the frameRate and frameDuration of the FootageItem.
Floating-point value in the range [1/99.. 1.0]; read-only for a FootageItem, otherwise read/write.