The event occurs when the next portion of video data (from a file or a camera) is received.
type // defined in MRVType unit
TRVCamProgressEvent = procedure(Sender: TObject; BytesRead: Integer) of object;
property OnProgress: TRVCamProgressEvent;
BytesRead is a size of this new data portion. You can use this event to calculate how many bytes are received from a camera while playing a video.