Windows Media Audio
Windows Media Audio (WMA)
is a
proprietary
compressed
audio file format
developed 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. The ASF file format specifies how
metadata
about the file is to be encoded, akin to the
ID3
tags used by MP3 files. ASF is also
patented
in the United States. Files in this format can be played using
Windows Media Player
,
Winamp
(with certain limitations, DSP plugin support and DirectSound output is disabled using the default WMA plugin) 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 supports
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. The most current version of the format is Windows Media Audio 9.1 which includes specific codecs for
lossless
,
multi-channel surround sound
and voice encoding in addition to the main
lossy
codec. Both
constant
and
variable bit rate
encoding are supported.
See also
Windows Media Video
- the video counterpart
List of audio formats
External links
Windows Media Homepage at Microsoft
Description of the algorithm used for Windows Media encryption
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