Current applications are capable of achieving rates of up to 30 fps, the current standard for American television. Video compression begins by reducing the amount of information within an individual frame. Typically this is done by exploiting similarities between adjacent pixels and using smaller code words to encode a block of similar pixels. Once individual frames have been reduced, the compressor seeks a way to capitalize on redundancies between consecutive frames. If frame differencing is employed, the resulting data stream will contain only the differences between some reference frames.
Decompression is achieved by reversing the process, and is often much quicker.
There are certain aspects of frame differencing that can affect picture quality and movie file size. Frame differencing uses key frames as its basis. A key frame is one in which all of the data for that frame is stored and self-contained, and does not rely on any other frames. Key frames are what differenced frames are based on. Differenced frames only store information that differs from the key frame they are associated with.