The Windows Media Audio (WMA) system uses the waveform coding concepts of subband/transform coding, quantization, and variable length coding to achieve its compression. In addition it models properties of human auditory system to achieve the highest quality of audio even at low data rates. The WMA encoder and decoder systems are shown in Figure 1 and Figure 2 respectively. This document focuses on the WMA bitstream syntax and semantics, and describes the operation of the decoder.