Compaq ProLiant 1600 Video Streaming Technology - Page 8

ECG068/0798 WHITE PAPER (cont.) 8... deliver very many streams for most network delivery. To achieve further reduction in data rate, video compression is needed. Compressing-Codecs Different algorithms and techniques known as "codecs" have been developed for compressing video signals. Video compression techniques take advantage of the fact that most information remains the same from frame to frame. For example, in a talking head video, most of the background scene typically remains the same while the facial expressions and other gestures change. Taking advantage of this enables the video information to be represented by a "key frame" with "delta" frames containing the changes between the frames. This is typically called "interframe" compression. In addition, individual frames may be compressed using lossy algorithms similar to JPEG photo-image compression. An example of this is the conversion from RGB to the Y/C color space described above where some color information is lost. This type of compression is referred to as "intraframe" compression. Combining these two techniques can result in up to 200:1 compression. This compression is achieved through the use of a "codec"-an encoder/decoder pair, depicted as follows. Video In AVI QuickTime Files Encoder Streaming Files Transmit 100111001100010 Store Decoder Video Out To Display A "Codec" is a combination of an EnCoder and a decoder Codecs vary depending on their purpose, for example, wide bandwidth vs. narrow bandwidth or CD-ROM vs. network streaming. Encoders generally accept file types such as Audio/Video Interleave (AVI) and convert them into proprietary streaming formats for storage or transmission to the decoder. Multiple files may be produced corresponding to the various bit rates supported by the codec. A codec may also be asymmetric or symmetric depending on whether it takes longer to encode than decode. Some codecs are very compute intensive on the encode side and are used primarily for creating content once that will be played many times. Symmetric codecs, on the other hand, are often used in real-time applications such as live broadcasts. A number of codecs have been developed specifically for CD-ROMs while others have been developed specifically for streaming video. Proprietary CD-ROM Codecs Proprietary Streaming Codecs Cinepak Indeo TrueMotionS Smacker Video 1 Power!VideoPro MPEG Vxtreme ClearVideo VDOLive Vivo RealVideo TrueStream Xing Codec Types