The emergence of various digital video technologies in industries such as broadcast television, communications networks, consumer electronics, and multimedia computers continues to increase at a remarkable rate. This widespread use of digital video applications is motivated by the fact that signal processing, editing and data transfer of digital information is much easier compared with processing of analog representations. But as importantly, digital video owes its popularity to the several standards that have been created for digital video compression in recent years.
Digital video compression solutions are arguably the most important component of any digital video platform. Since digital video is known to contain an enormous amount of information in uncompressed format, its manipulation, storage, and transmission can be very time consuming and expensive, if not impossible. As a result, digital video compression techniques have been devised to reduce the overwhelming volume of data while preserving the perceptual quality of its content. A compatible video decompression scheme is then used to uncompress the data for playback.
The MPEG-2 International Standard formed by the Moving Pictures and Expert Group, and described in ISO/IEC 13818-2, “Information Technology—Generic Coding of Moving Pictures and Associated Audio Information: Video 1996,” which is hereby incorporated herein by reference in its entirety, is intended to standardize compression for the industries noted above. The ISO MPEG-2 standard specifies the syntax of the encoded bitstream and semantics of the decoding process. The choice of coding parameters and tradeoffs in performance versus complexity, however, are left to the encoder developer.
The efficiency of the MPEG-2 encoding system is assessed by the fidelity of the perceived video transmitted over a fixed communication bandwidth or stored into a digital medium. For some applications, such as digital satellite systems, multiple programs are multiplexed into a single large stream for broadcasting, and a bank of MPEG-2 encoders is used to monitor and encode all programs, while attempting to maintain the quality of the received channels. The MPEG-2 stream is sent over either a fixed communications bandwidth or a dynamic bandwidth as in asynchronous transfer mode (ATM) networks.
In typical statistical multiplexing systems, such as direct broadcast satellite (DBS) applications, several video bitstreams (or programs) are multiplexed onto one single constant bit rate channel. Unfortunately, encoding of each program at a predefined constant bit rate can lead to picture quality degradation due to changes of scene content in the programs over time. The problem becomes more complex if the operation of the encoders is not aligned in time, such as when coding varies among the encoders with respect to differing group-of-pictures (GOP) structures and/or differing picture-encode start times.
A need thus exists in the art for a multi-program compression technique which dynamically distributes available bandwidth among programs in order to optimize overall video quality of the system. The present invention provides such a technique by employing a joint rate control strategy which guides the individual encoders dynamically during the encoding process.