Usage of MPEG-2 systems by applications and application standardization bodies.
MPEG specifies carriage across MPEG-2 system streams of content without imposing any constraints on the parameters used in the coded content, such as sampling frequencies and frame rates. Only by means of levels and profiles can constraints be signalled on the carried content. However, regionally often only a sub-set of the available parameter values needs to be supported. For example, in regions where only 60 Hz based video is used, there is often no need to support 50 Hz based video and vice versa. Obviously, this means loss of interoperability, but in practice this is a minor issue; at the time of the initial deployment of MPEG-2 system decoders, saving the decoder complexity1 involved with supporting practically un-used frame rates was considered far more important. In addition also business reasons for non-interoperable application domains may exist (see Note 17.1).