Methods and systems for compressing and transmitting media signals are known in the art. Compressed digital video is largely becoming the preferred medium to transmit to video viewers everywhere. Part of the Moving Pictures Experts Group (MPEG) specifications are standardized methods for compressing and transmitting video. Various audio compression techniques are also known in the art. In general, MPEG is used today for transmitting video over terrestrial, wireless, satellite and cable communication channels and also for storing digital video.
An audio stream is organized as an ordered sequence of frames. A video stream is usually organized as an ordered sequence of pictures, each picture includes a plurality of pixels. A video picture includes a plurality of slices, each slice including a plurality of macro blocks. The audio and video streams are provided to an audio encoder and video encoder respectively to generate compressed audio and video elementary streams, also referred to as elementary streams.
MPEG compression/encoding utilizes various compression schemes, such as adaptive quantization, intra-frame encoding, inter-frame encoding, run length encoding and variable length coding. Intra-frame coding takes advantage of spatial redundancies in a picture. Inter-frame coding takes advantage of temporal redundancies from picture to picture in a video sequence. Inter-frame coding involves motion estimation and motion compensation. There are three types of motion estimations—forward, backward and bidirectional. Macroblocks are the elementary unit for motion compensation and adaptive quantization. Each macroblock is associated with a quantization factor field, representative of the degree of quantization. A slice, including a plurality of macroblocks includes a slice header that has a quantization factor field that is associated to some of the macro blocks of the slice.
Elementary streams are packetized to produce PES packets. PES packets made up of elementary streams that form a program share a common time base. The PES packets may also include additional information. PES packets of distinct elementary streams can be arranged as either a Program Stream or a Transport Stream. At least one or more stream of PES packets having a common base time are usually combined to a Program Stream. A Transport Stream combines one or more programs with one or more independent time bases into a single stream. Transport Streams include transport packets of 188 bytes. Transport Stream packets start with a transport packet header. The header includes a packet ID (PID). Transport Stream packets of one PID value carry data of a single elementary stream. Transport Streams include Program Specific Information (PSI) tables. The PSI tables specify which PIDs and accordingly which elementary streams are associated to form each program.
Transport Streams may be of either fixed or variable bit rate. Some programs of the Transport Stream are of a variable bit rate, if, for example, more bits are allocated to complex scenes, and less bits are allocated to more simple scenes.
Transport Streams are provided to a channel of a limited available bandwidth/storage space. The ISO/IEC 13818-1 specification defines a channel as a digital medium that stores or transports a Transport or a Program Stream. The aggregate bandwidth of all the components of the Transport Stream must not exceed, at any time, the available bandwidth of the channel.
Various lossy and lossless techniques are implemented to adapt the aggregate bandwidth of the programs of a Transport Stream to the available bandwidth of a channel. U.S. Pat. Nos. 6,038,256 and 6,192,083 of Linzer et al, U.S. Pat. Nos. 5,862,140 and 5,956,088 of Shen et al and U.S. Pat. No. 5,877,812 of Krause et al, describe some of these prior art methods. Lossless techniques, such as statistical multiplexing, do not require further compressing of media pictures. Lossless techniques also include delaying or advancing a transmission of transport packets. Lossy techniques involve additional compression, and are usually implemented whenever the appliance of lossless techniques is not feasible or does not provide sufficient results. The further compression usually results in visual quality degradation.
Systems and methods for providing guarantying quality of service, mainly for data streams are known in the art. Various methods for providing quality of service are illustrated at the following patents: U.S. Pat. No. 5,956,482 of Agraharam et al, U.S. Pat. No. 5,995,490 of Shaffer et al, U.S. Pat. No. 6,005,851 of Craddock et al, U.S. Pat. No. 6,028,842 of Chapman et al, and U.S. Pat. No. 6,246,702 of Fellman et al.
Prior art methods of providing quality of service guarantees did not utilize the bandwidth in an efficient manner as they did not implement compression techniques.
There is a need to provide a system and method for efficiently utilizing the bandwidth of communication channels and provide quality of service guarantees.
There is an efficient system and method for scheduling the transmission of compressible and non-compressible packets over a communication medium.
There is a need to provide a system and method for providing quality of service guarantees while utilizing compression techniques.