Windows Media Audio
Windows Media Audio (
WMA) is a
proprietary compressed audio file format developed by
Microsoft. It was initially intended to be a competitor to the popular
MP3 format, though in terms of popularity of WMA files versus mp3 files, this never came close to occuring. With the introduction of
Apple's
iTunes Music Store, WMA has positioned itself as a competitor to the
Advanced Audio Coding format used by Apple and is part of Microsoft's
Windows Media framework.
A large number of consumer devices, ranging from portable hand-held music players and handphones to set-top DVD players, support the playback of WMA files. WMA is second only to MP3 in popularity in terms of number of devices supported.
Files in this format can be played using
Windows Media Player,
MPlayer,
Winamp (with certain limitations, DSP plugin support and DirectSound output is disabled using the default WMA plugin),
Real Player, and many other media players. The
FFmpeg project has reverse-engineered and reimplemented the WMA format to allow its use on
POSIX compliant operating systems such as
Linux.
In November 2005, a new update was available for the
PlayStation Portable (version 2.60) which allowed WMA files to be played on the console for the first time.
An initial reason for the development of WMA may have been that MP3 technology is
patented and has to be licensed from
Thomson SA for inclusion in the
Microsoft Windows operating system.
WMA is capable of
VBR,
CBR and lossless audio encoding in order to be marketed as a versatile format.
Windows Media Audio can optionally support
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.
A WMA file is often encapsulated in an
Advanced Systems Format (ASF) file. The resulting file may have the
extension "wma" or "asf" with the "wma" extension 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.
WMA began being widely distributed starting with the WMA 7
lossy compression based codec and has now reached version 9. Microsoft's WMA bundle also includes three more codecs, a Windows Media Audio 9 Voice codec, Windows Media Audio 9
lossless codec and Windows Media Audio 10 Professional codec (earlier known as WMA 9 Pro). The WMA 10 Pro codec is based on a completely different technology (superior to "ordinary" WMA in terms of quality and features) and thus WMA 10 Pro files are incompatible with older players. WMA 10 Pro supports 96 KHz 24-bit audio as well as 5.1/7.1 multi-channel audio.
Windows Media Player 11 however is the latest version of Microsoft's media player.
More information about WMA can be found in here:http://www.microsoft.com/windows/windowsmedia/forpros/codecs/audio.aspx
Initially Microsoft
claimed that files in WMA format sounded better than MP3 files at the same bitrate; Microsoft also claimed that WMA files sounded better than MP3 files at higher bitrates. Although claims about audio quality should be taken with caution, double blind tests with other
lossy audio codecs have consistently failed to support Microsoft's claims about its superior quality:
* At 128 kb/s an
independent test (However, due to lack of reference of encoder used in this test, the test result is well known to be unreliable.) conducted in 2004 showed that it was roughly equivalent to MP3 encoded with
LAME encoder, inferior to
AAC and
Vorbis, and superior to
ATRAC3. (The test didn't reference which ATRAC3 encoder they were using. This issue is especially important for ATRAC3, since Sony herself didn't implement her top quality DSP Type S algorithm into PC platform in order to protect MD business, immediately marked all PC based test as an unreliable source for ATRAC codec)
* At 128kb/s the
most recent large scale test shows a four way tie between aoTuV
Vorbis,
LAME-encoded
MP3, WMA Pro and
iTunes (
QuickTime)
AAC, with each codec essentially transparent (sounds identical to the original music file). However, device and player support for WMA Pro is not as prevalent as WMA Standard. Generally speaking, WMA (without any other qualifiers) refers to the WMA Standard.
* At mid-low bitrates, latest private tests (
80 kb/s,
96 kb/s) shows that WMA has a lower quality than the lossy audio codecs AAC (HE and LC) and Vorbis, a roughly equivalent quality than MP3, and a better quality than
MPC.
While the Windows Media Audio codec itself does not contain any
digital rights management facilities, the
Advanced Systems Format (ASF) container format, in which a WMA stream may be encapsulated, can.
Janus is the codename for a recent version of Windows Media DRM, which is sometimes used in conjunction with WMA. The DRM technology supports time-limited music such as those offered by unlimited download services, such as
Napster,
Yahoo! Music Unlimited and Virgin Digital. Janus DRM is incompatible with most portable audio devices since they typically support up to WMA DRM Version 9. CD tracks ripped with Windows Media Player are "protected" (DRM-restricted) by default, though this setting can be changed.
*
Windows Media Video - the video counterpart
*
Windows Media DRM - The Microsoft
DRM technology, often used in WMA files.
*
List of audio formats*
Comparison of audio codecs*
MP3*
Windows Media Homepage at Microsoft*
Listening tests (performed between 2002 & 2004) featuring Windows Media Audio at several bitrates*
WMA page in Hydrogenaudio Wiki*
Description of the algorithm used for Windows Media encryption*
WMA Decoder Source Code at FFMpeg's CVS
