Windows Media Audio also called WMA is a format owner of audio compression of type “lossy” (destroying) developed by Microsoft. Format WMA makes it possible to protect as of the encoding the output files against illegal copying by a named technique numerical Gestion of the rights (or GND).

The format exists in four forms:

• the Standard WMA, the first with being left, most widespread on Internet and the only one with being readable (currently) on many walkmen;
• the WMA Pro, theoretically of better quality but much less widespread.
• the WMA Lossless which offers a sound quality identical to the original, a serious competitor with formats without loss like Monkeys Audio or Flac
• the WMA Voice, especially dedicated to the encoding of the voice and this, with low flow (less than or equal to 20 kbit/s)

Both are able to code in constant flow (Constant bit misses - CBR) or in variable flow (VBR). The codec wma is among all the formats of encoding with losses available one of fastest.

With the WMA, one finds the levels of quality VBR 100,98,90,75,50,25,10. The figures do not have any relationship with the flow. It is in fact the “theoretical” percentage of quality compared to the original file, but it is only about one arbitrary reference mark, a fraction of musical quality not having any significance in oneself.

• 100 corresponds to the file its not compressed and does not have a theoretical equivalent CBR
• 98 corresponds approximately to a CBR of 320 kbits/s;
• 90 corresponds approximately to a CBR of 192 kbits/s;
• 75 corresponds approximately to a CBR of 112-128 kbits/s;
• 50 corresponds approximately to a CBR of 64-80 kbits/s.

This correspondence theoretical quality and flow in CBR are worth also for new the codecs 9.1 and 9.2 left respectively in 2004 and 2006.