The present invention relates generally to an apparatus for the distribution and delivery of video in a digital system and, in particular, to a method and apparatus that rapidly changes the channel in such a system.
In a typical analog cable system all of the channels or services ordered by the subscriber are delivered to each subscriber""s home. In order to ensure that each subscriber receives only the channels for which he has paid, the cable television providers encrypt or xe2x80x9cscramblexe2x80x9d the premium channels (HBO, CINEMAX, DISNEY, etc.). The cable television providers also may scramble many of the xe2x80x9cbasicxe2x80x9d channels (local stations, ESPN, MTV, VH1, TNT, DISCOVERY, etc.). Therefore, even though virtually all television sets sold today are cable-ready, most subscribers still need a set-top unit (sometimes referred to as a cable box in the cable television environment) to descramble the signals. The set-top units are located proximate a television and are also used to change the channel that is viewed on the television.
Subscribers, especially residential subscribers, are demanding that large amounts of information and more choices of services be brought into their homes. Switched video for viewing on a subscriber""s television and high-speed Internet access are two services highly desired by subscribers. In order to meet the demand, and to accommodate the recently approved high-definition television standards, the new services will likely have to be capable of handling digital signals.
In addition to the emerging technologies, entry of the Regional Bell Operating Companies (RBOCs) have made digital delivery systems economically feasible. A typical digital video delivery system includes a means for receiving the video signals from various broadcast sources, a means for delivering the signals to a plurality of subscribers, and a means of transmitting the signals between the receiving means and delivering means. The means for receiving the video signals may include a broadband digital terminal (BDT) located in a central office. The delivering means may be a broadband network unit (BNU) located preferably on a telephone pole or other convenient location proximate a number of subscribers. Cable or optical fiber connects the BDT to the BNU. A second cable (or a twisted wire pair) connects the set-top units (and, if required, the various other units in the subscriber""s home) with the BNU.
In a typical digital video system, all of the video services offered by the video service company are again delivered to the set-top unit. When selecting a new channel, the set-top unit performs the actual switching and also descrambles the digital signals.
Even though the premium channels are scrambled, delivering all of the video signals into a subscriber""s home makes the video services susceptible to theft. Accordingly, more complexxe2x80x94and expensivexe2x80x94steps must be taken to further secure the transmission and delivery of the video services.
A solution to the theft problem is to perform the channel switching xe2x80x9cupstreamxe2x80x9d from the subscriber at a facility controlled by the video provider (in a digital system at the BDT, for, example), and only delivering one channel at a time to the subscriber""s set-top unit. Another advantage of moving the switching upstream is that the bandwidth requirements of the overall video delivery system are greatly reduced. However, a drawback of this system is that the subscriber experiences a time delay between the period of time it takes for the subscriber to select a channel and for the newly selected channel to be viewed on the television.
The reason for this time delay is that the subscriber""s request must first travel upstream to the BDT; next, the BDT must acknowledge the request, then synchronize and xe2x80x9clock onxe2x80x9d to the desired video service; finally, the BDT must transmit the desired video service back downstream to the subscriber. The overall delay between each channel change can take over a second.
A significant portion of the delay is caused by the time it takes for the video signal to synchronize. This portion accounts for about half of the overall delay (i.e., about a half second). Many subscribers find the delay in such video delivery systems annoying since they are accustomed to seeing the broadcast signal immediately after selecting a new channel. Most subscribers find that a one second delay is unacceptable, which would make such a system competitively unattractive.
The present invention relates to a method and apparatus for rapidly changing the channel in a digital video delivery system. The rapid channel changer will be preferably located in the central office with the broadband digital terminal (BDT) and indexes the xe2x80x9cstartxe2x80x9d or synchronization frame of each video channel received at the BDT.
Each digital video signal includes a synchronization frame. The subject channel changer captures the multiple compressed video signals and stores each signal in a cache buffer. A, processor is used to index or xe2x80x9cpoint toxe2x80x9d the respective synchronization frames for each buffered signal.
When a subscriber requests a specific channel or video service, the processor can immediately access the requested video signal at a synchronization frame and direct the video stream to the subscriber since the processor already has the position of the synchronization frame of each video signal. Accordingly, the period of time that the subscriber previously had to wait for the synchronization frame is eliminated.
These and other features and objects of the invention will be more fully understood from the following detailed description of the preferred embodiments which should be read in light of the accompanying drawings.