Overview
The MPEG compression methodology is considered asymmetric as the encoder is more complex than the decoder. The encoder needs to be algorithmic or adaptive whereas the decoder is 'dumb' and carries out fixed actions. This is considered advantageous in applications such as broadcasting where the number of expensive complex encoders is small but the number of simple inexpensive decoders is large. The MPEG's (ISO's) approach to standardization is novel, because it is not the encoder that is standardized, but the way a decoder interprets the bitstream. A decoder that can interpret the bitstream is said to be compliant. The advantage of standardizing the decoder is that over time encoding algorithms can improve, yet compliant decoders continue to function with them. The MPEG standards give very little information regarding structure and operation of the encoder and implementers can supply encoders using proprietary algorithms. This gives scope for competition between different encoder designs, which means better designs can evolve and users have greater choice, because encoders of different levels of cost and complexity can exist, yet a compliant decoder operates with all of them.
MPEG also standardizes the protocol and syntax under which it is possible to combine or multiplex audio data with video data to produce a digital equivalent of a television program. Many such programs can be multiplexed and MPEG defines the way such multiplexes can be created and transported. The definitions include the metadata used by decoders to demultiplex correctly.
Read more about this topic: Moving Picture Experts Group