High Picture Quality at Low Bitrates
It is no exaggeration to say that compression is the key technology that makes digital video feasible. The reason is simple: digital video generates astronomical numbers of bits. Uncompressed, a single second of SD video comprises about 250 megabits of data (480 lines/frame x 720 pixels/line x 24 bits/pixel x 30 frames/second). HD formats (1080 lines/frame x 1920 pixels/line) multiply this number by another factor of six, generating 1.5 gigabits of data every second. Uncompressed, a 2 hour HD movie adds up to 10.8 terabits (1.35 terabytes) of data. There is no commercially feasible technology that allows bits to be either transmitted or stored in such overwhelming numbers. (See Digital Video Basics for more information.)
For this reason, it is more than merely desirable to compress digital video. Compression is the essential precursor to any other operation on a digital video stream. Fortunately, because most bits are either redundant or unimportant in video data, video compression is an extremely powerful technology. Using advanced compression technology like H.264/AVC, it is literally possible to discard 99 out of every 100 bits in an uncompressed source and still retain excellent video quality. (See Video Compression Basics for more information.)
The goal for video compression technology can be stated simply: to eliminate bits in inverse order of their importance to picture quality. In practice, this means that an encoder should generate the best possible pictures for any given bit rate. An HD video stream compressed to 15 Mbps (a 100:1 reduction from uncompressed source at 1.5 Gbps) clearly cannot retain all the information in the original source stream, but the differences from the original ought to be as close to undetectable by the human visual system as possible. Further compression of the same stream ought to result in graceful degradation of video quality, achieving the best picture possible at each lower bit rate. For example, the video quality at 5 Mbps (a 300:1 reduction) ought to retain as much quality as possible despite additionally eliminating two out of every three bits in the 15Mbps stream. (See Digital Color Coding for an example of "lossy" compression, where key information is retained and less important information is discarded.)
This goal is precisely the ambition behind Telairity encoders, which use Telairity's exclusive hardware and software encoding technology, including Telairity's exclusive T1P2000 video processor and associated direct execution AVClairity software, to achieve industry-leading picture quality for both HD and SD formats at the lowest bitrates available. More specifically, Telairity offers three lines of encoders for customers seeking to maximize picture quality while minimizing bandwidth and storage requirements. The three lines are distinguished by three different levels of video processing capability: an entry-level two processor line for SD formats, an advanced four processor line for SD and mobile formats, and an eight processor line for HD formats.
7000 Series Economy SD Encoders (2 T1P2000 video processors)
Bit rates between 1 and 8 Mbps. 8 Mbps is indistinguishable from source for many casual viewers. 2 Mbps provides acceptable picture quality on a wide range of material; content with relatively little action may be acceptable at lower bit rates. Compared to a typical 4 Mbps MPEG-2 SD compression stream, a 7000-series encoder achieves similar picture quality in half the bandwidth.
9000 Series High Compression SD Encoders (4 T1P2000 video processors)
Bit rates between 0.1 and 5Mbps. With twice the compute power of 7000 series SD encoders, 9000 series SD encoders implement a much richer set of compression tools for maximum compression. Full SD formats can be reduced to as little as 500Kbps, a 500-to-1 reduction in bit rate compared to uncompressed source. Bit rates below 500Kbps produce excellent picture quality for small format mobile screens.
8000 Series HD Encoders (8 T1P2000 video processors)
Bit rates between 2 and 15 Mbps. 15 Mbps is indistinguishable from source for many casual viewers, 5 Mbps provides acceptable picture quality on a wide range of material; content with relatively little action (e.g., studio talk shows) may be acceptable at lower bit rates. Compared to a typical 19.2 Mbps MPEG-2 HD compression stream, an 8000-series encoder will allow up to 4 HD channels to share the same bandwidth.
For SD formats, the choice between a 7000 series and a 9000 series SD encoder hinges on the question of available bandwidth. Facilities with a fixed number of channels and ample bandwidth available per channel can save money by buying a less expensive 7000 series encoder with no compromise in picture quality.
Facilities that want either to save money by using less bandwidth, or to increase revenues by fitting more channels into the available bandwidth, are generally better served by purchasing high compression 9000 series encoders. Wherever higher bandwidth requirements mean higher costs or less choice, 9000 series encoders can repay their purchase cost many times over with the daily savings or higher revenues generated by better bandwidth efficiency.
