Analog video data, for example, a motion picture or a television program, may be presented as a digital video data stream from a digital video provider, e.g., in digital cable television, digital satellite television or computer network-downloading environments. A digital video provider may be, e.g., a network server, a digital cable television provider or a digital satellite television provider.
A digital video data stream may be compressed into frames, specifically base frames and reference frames, so that it utilizes less bandwidth in a data transmission channel, also referred to herein as a channel. Compression techniques include, e.g., Motion Picture Experts Group (MPEG), Motion Joint Photographic Experts Group (M-JPEG), and digital satellite systems standards. See, e.g., International Organization for Standardization (ISO), Coding of Moving Pictures and Audio, “MPEG-2 Generic Coding of Moving Pictures and Associated Audio Information,” October 2000; “Overview of the MPEG-4 Standard,” March 2002; ISO/International Electrotechnical Commission (IEC) 15444-3:2002, “Information Technology—JPEG 2000 Image Coding System—Part 3: Motion JPEG 2000;” and Advanced Television Systems Committee (ATSC) “Modulation and Coding Requirements for Digital TV (DTV) Applications over Satellite,” July 1999.
A base frame is a still picture that shows an image; it includes sufficient data for a viewer to identify the content of a digital video data stream to which the base frame belongs. A reference frame is a still picture that shows only the differences between the image in the reference frame and the image in a base frame upon which the reference frame is based. Typically, frames are separated into groups of frames (GOF) that start at a base frame and include any number of reference frames and additional base frames.
FIG. 1 illustrates an example of a compressed digital video data stream. Channel 100 carries compressed digital video data stream (DVDS) 102, which is separated into any number n of GOFs, e.g., GOF-1, GOF-2 through GOF-n. A GOF, e.g., GOF-1 104, includes any number n of frames, frame-1, frame-2, etc. through frame-n, where each frame is either a base frame (BF) or a reference frame (RF).
MPEG, for example, compresses a digital video data stream into individual frames known as intra-frames (I-frames), predictive frames (P-frames) and bi-directional frames (B-frames). Generally speaking, an I-frame is a base frame that serves as a reference for P-frames and B-frames, which are thus reference frames. A P-frame describes the difference between the P-frame and the I-frame upon which it is based. Similarly, a B-frame describes the difference between the B-frame and a previous I-frame or P-frame and the difference between the B-frame and a following I-frame or P-frame.
A digital video receiver, e.g., a computer system, such as a desktop computer, a personal digital assistant (PDA), a laptop or palmtop computer, a cellular phone, a network access device, etc., or a set-top box, e.g., a digital cable television receiver or digital satellite television receiver, receives a compressed digital video data stream and decompresses the digital video data stream for display on a display device. A display device may be, but is not limited to, a television screen or computer system display device, e.g., a cathode ray tube (CRT) or a liquid crystal display (LCD).
At startup of a digital video receiver, or when the digital video receiver switches from one channel to another, e.g., because of user input from a remote control device or a push-button on the digital video receiver, the digital video receiver may execute a number of processes to receive and decompress a digital video data stream. These processes may include, e.g., locking onto a channel (e.g., by tuning to the frequency of the channel), acquiring a compressed digital video data stream on the channel, demodulating and decoding the compressed digital video data stream and providing a decompressed digital video data stream for display. As used herein, decompression includes the processes from startup of a digital video receiver, receipt of an indication to switch from one channel to another, or receipt of an indication to switch from a video device input mode (e.g., a digital video disc player) to a satellite, cable or antenna input mode, through presentation of a decompressed digital video data stream for display.
During decompression, a digital video receiver typically identifies a base frame that starts a GOF, decompresses the compressed digital video data stream one GOF at a time and presents each decompressed GOF for display. This typically results in a time delay between startup of the digital video receiver, or receiving an indication to switch from one channel to another, and displaying a decompressed GOF. During the time delay, a display device typically presents a blank screen to a viewer. This blank screen may appear for several seconds, which may be undesirable if the viewer wants to know relatively quickly the content of a digital video data stream on a particular channel, so that the viewer can decide whether to watch that channel.