Windows Media Audio
Windows Media Audio is a proprietary compressed audio file format used by Microsoft. It was initially a competitor to the MP3 format, but with the introduction of Apple's iTunes Music Store, it has positioned itself as a competitor to the advanced audio coding format used by Apple. It is part of the Windows Media framework. An initial reason for the development of WMA might have been that MP3 technology is patented and has to be licensed from Thomson for inclusion in the Microsoft Windows operating system.
A WMA file is almost always encapsulated in an Advanced Systems Format (ASF) file. The resulting file may have the filename suffix "wma" or "asf" with the "wma" suffix being used only if the file is strictly audio.
Files in this format can be played using Windows Media Player, Winamp and many other alternative media players. The FFmpeg project have reverse-engineered and reimplemented the WMA format to allow its use on POSIX compliant operating systems such as Linux.
Windows Media Audio features digital rights management using a combination of elliptic curve cryptography key exchange, DES block cipher, a custom block cipher, RC4 stream cipher and the SHA-1 hashing function.
With the advent of Windows Media Audio 9, a new lossless codec has been introduced to accompany the existing lossy codec. Support for variable bit rates has also been introduced.
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