Frames per second.
Expressed as a fraction so that rates such as 29.97 (precisely 30000/1001) are represented accurately.
Note
Specifying a 0 or invalid rate (see MediaRational.isValid) indicates the video track uses Variable Frame Rate (VFR). In this mode of operation, because there is no pre-defined frame duration, all frames added through MediaEncoder.AddFrame must use the overload that receives a MediaTime.