Media UK

Bitrate

When listening to or viewing a stream on the Internet, or listening to a DAB radio, or viewing a programme on the Freeview or Sky Digital platforms, one is actually downloading (over some transmission system) a bitstream; in essence, just a long string of ones and zeroes corresponding to some digitised representation of the content.

A raw digital representation of an audio or television broadcast is too large to conveniently transmit or send over the Internet, Therefore, mathematical models are used to decide which parts of the original content are least essential to the quality of the broadcast; these are then discarded, reducing the quantity of data per second that need be transmitted.

This quantity is the bitrate of the stream; the higher the bitrate, the less information which must be discarded in the encoding process. In principle, the higher the bitrate of a stream, the better quality it should be; the perceived quality, however, also depends heavily on the mathematical model ("codec", standing for coder/decoder) used in the compression process.

Typically, DAB transmissions in the UK are at a bitrate of around 128 kilobits per second (around 128,000 ones or zeroes per second), using the MP2 (MPEG-1 Audio Layer 2) codec. Internet streams are found at anywhere from 32 to 256 kbps.