Method of and apparatus for generating a precise frame rate in digital video transmission from a computer system to a digital video device

摘要

A method of and apparatus for transmitting an isochronous video stream of data at a desired frame rate from a source device to a receiving device. A video frame is part of an isochronous stream of video data which is transmitted over an IEEE 1394-1995 serial bus network. The desired frame rate is determined by the receiving device. The source device preferably determines a proper ratio of data packets versus video frames in response to the particular frame rate required and a cycle time for isochronous data. This ratio of data packets versus video frames rarely computes to an integer result. Accordingly, the source device preferably generates two groups of frames. A first group contains an integer value of packets nearest to and above the desired overall average ratio of data packets versus video frames. The source device generates a second group of frames where each frame from this second group contains an integer value of packets nearest to and below the ratio of packets versus video frames. To achieve the desired frame rate, the source device generates a frame ratio containing a specific number of frames from the first group and the second group and forms the isochronous stream of video data. The source device serially generates each of the frames in an order including a combination of the first group of frames and the second group of frames to achieve the overall desired average frame ratio. The source device then transmits the resulting isochronous video stream of data to the receiving device at the desired frame rate.