HP ProLiant 1600 Video Streaming Technology - Page 6

ECG068/0798 WHITE PAPER (cont.) 6... The '4' in the above descriptions indicates that luma is sampled at 4 times the basic 3.375 MHz frequency and the '1' and '2' indicates that the chroma is sub-sampled at 1 or 2 times the basic frequency. This approach to storing and transmitting video has the advantage of enabling file size reduction without any noticeable impact to the human eye on picture quality. Since, the eye detects subtle variations in brightness easier than differences in color, more bits are typically used to represent brightness with fewer bits representing color information. In this scheme each video pixel has its own luma, or Y, value, but groups of pixels may share CrCb chroma values. Even though some color information is lost, it is not noticeable to the human eye. Depending on the format used, this conversion can result in a 1/3 to 1/2 reduction in file size. The color bits required per pixel for each of these formats is 24 (4:4:4), 16 (4:2:2), and 12 (4:1:1). Network Delivery Challenges The bandwidth required by video is simply too great to squeeze through narrow data pipes. For example, full-screen/full-motion video can require a data rate of 216 MegaBits per second (Mbps). This far exceeds the highest data rate achievable through most networks or across the bus of older PCs. Until recently, the only practical ways to get video on a PC were to play video from a CD-ROM or to download a very large file across the network for playback at the user's desktop. Neither of these approaches is acceptable for delivery of content across a network. The Bandwidth Problem The scope of this problem can be seen by looking at the following illustration of available bandwidth for several methods of data delivery. Technology Fast Ethernet Ethernet Cable Modem ADSL 1x CD-ROM Dual channel ISDN Single channel ISDN High speed modem Standard modem Throughput 100Mbps 10Mbps 8Mbps 6Mbps 1.2Mbps 128Kbps 64Kbps 56Kbps 28.8Kbps Uncompressed video at 216Mbps and above, won't squeeze through these pipes As can be seen from this illustration, even a high bandwidth Ethernet LAN connection cannot handle the bandwidth of raw uncompressed full-screen/full-motion video. A substantial amount of video data compression is necessary. Successfully delivering digital video over networks can involve processing the video using three basic methods: 1. Scaling the video to smaller window sizes. This is especially important for low bandwidth access networks such as the Internet, where many clients have modem access.