We already described that emerging Internet standards for real-time video streaming that allow a great deal of flexibility in design. But we have not seen many offers from vendors that exploit this flexibility. Push server vendors offer great hardware and only generic software. Famous Internet sites usually do not offer search capabilities and do not distribute the broadcasting servers to provide better video transfer performance. We first describe the design goals of SBVS
First we chose the video source to be satellite TV, set-top-box or VCR. Those sources combined with cheap MPEG1 encoder require a bandwidth of 150 Kbytes/sec or a storage space of 1 Gigabyte per hour. So we can build the system based on simple PC's and we don't need to impose any additional requirements on the networking hardware. Next, dropping storage prices allow us to use redundant storage servers to reduce network traffic and improve the video quality. If we install 40 Gigs of the cheap storage per node, we still have the space to keep 10-20 hours of movies and 20-30 hours of recycled scheduler-based video. For example, we can keep one week of news programs assuming we record up to 3 hours of news every day.
Once we decide to focus on TV programs, we must pay most of our attention to the way the content is to be accessed. For example, typical news programs represent just talking heads, so indexing based on periodically taken screen-shots is relatively useless. So we decided to put the same attention to closed caption text as to the video itself. Closed captions are the main way to index and navigate in SBSVS. We have implemented a comprehensive search capability based on keywords connected by boolean expressions. The next step should be the incorporation of the speech recognition program if closed captions are not available. At present, the computational power of a commodity PC is not sufficient to process the text coming with the speed of TV show.
The second very useful feature is the synchronous delivery of text and video, thus providing the user with the way to read the text with the position mark indicating the current text.
SBSVS should be capable of live broadcast of a video channel as well as replay any stored material on demand. Another important feature is the ability of authorized user to initiate the recording of the channel he is watching. The recording of video must be performed using a reliable protocol, such as TCP, because we want to preserve the quality of the video, which is subject of repeated replays. But the real-time broadcast must be performed by UDP protocol, so that late packets would not be resent.
The main goal of the scheduler is to fill the storage with the video content, such as news programs and regular shows. Combined with closed captions search this provides the user with a way to keep one-week news accessible and organized. It may be reasonable to keep closed captions of expired movies if desired, but this is not implemented. Another important feature of the scheduler is the possibility to set up the time-to-live for each recording. Thus, for example, we can remove all three-day old news programs, but keep several weeks worth of the Mad show.