/** Called to request encoding of the next video frame in the DCP. This is called in order,
* so each time the supplied frame is the one after the previous one.
* pv represents one video frame, and could be empty if there is nothing to encode
/** Called to request encoding of the next video frame in the DCP. This is called in order,
* so each time the supplied frame is the one after the previous one.
* pv represents one video frame, and could be empty if there is nothing to encode