The MPEG-2 Systems Standard specifies two methods for multiplexing the audio, video and other data into a format suitable for transmission and storage, namely the program stream and the transport stream. The Program Stream is designed for applications where errors are unlikely. It contains audio, video and data bitstreams (also called elementary bitstreams) all merged into a single bitstream. The program stream, as well as each of the elementary bitstreams, may be a fixed or variable bit rate. The Transport Stream, using fixed-size packets of 188 bytes, is designed for applications where data loss is likely. Also containing audio, video and data bitstreams all merged into a single bitstream, multiple programs can be carried.