The chief function of MPEG Audio compression is to allow it to be synchronized with (i.e., played fast enough for) the compressed video.

The standard doesn't specify how to encode and there are several "layers" of audio encoding.

Currently, CD-quality encoding can be achieved with "Layer 3" (out of 5 layers) encoding.

Audio encoding is not as difficult as video encoding because wave values are being digitized rather than performing complex mathematical functions on huge blocks of pixels.