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Windows Media Audio ('''WMA''') is an Audio Data Compression technology developed by Microsoft . The name can be be used to refer to its Audio File Format or its Audio Codecs . It is a Proprietary technology which forms part of the Windows Media framework. WMA consists of four distinct codecs. The original WMA codec, known simply as ''WMA'', was conceived as a competitor to the popular MP3 and RealAudio codecs.12 It is the second most popular audio codec after MP3, based on the number of supported devices researched by Jupiter Research.3 ''WMA Pro'', a newer and more advanced codec, supports Multichannel and high Resolution audio.4 A Lossless codec, ''WMA Lossless'', compresses audio data without loss of audio fidelity. And ''WMA Voice'', targeted at voice content, applies compression using a range of low Bit Rates . DEVELOPMENT HISTORY The first WMA codec was based on the previous work from Henrique Malvar and his team.5 According to the published article, the technology was transferred over to the Windows Media team at Microsoft. Malvar was a senior researcher and manager of the Signal Processing Group at Microsoft Research ,6 whose team worked on the project called ''MSAudio''.7 The first finalized codec was at first referred as ''MSAudio 4.0''.89 It was later officially released as ''Windows Media Audio'',10 as part of Windows Media Technologies 4.0. Microsoft initially claimed that WMA delivers the same quality of MP3 at half the bit rate;11 Microsoft also claimed that WMA delivers "CD-quality" audio at 64 kbit/s. The former claim however was rejected by some audiophiles according to EDN.12 RealNetworks also challenged Microsoft's claims regarding WMA's superior audio quality compared to RealAudio. Newer versions of WMA became available: ''Windows Media Audio 2'' in 1999, Broadcom Corporation: Audio Codecs ''Windows Media Audio 7'' in 2000,13 ''Windows Media Audio 8'' in 2001,14 and ''Windows Media Audio 9'' in 2003. Microsoft first announced its plans to license WMA technology to third-parties in 1999.15 Although earlier versions of Windows Media Player played WMA files, support for WMA file creation was not added until the seventh version.16 In 2003, Microsoft released new audio codecs which were not compatible with the original WMA codec. These codecs were ''Windows Media Audio 9 Professional'', ''Windows Media Audio 9 Lossless'', and ''Windows Media Audio 9 Voice''. CONTAINER FORMAT See Also: Advanced Systems Format A WMA file is in most circumstances about the file is to be encoded, similar to the ID3 tags used by MP3 files. Metadata may include song name, track number, artist name, and also Audio Normalization values. This container can optionally support Digital Rights Management (DRM) 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. CODECS Windows Media Audio Windows Media Audio (WMA) is the most common codec of the four WMA codecs. Colloquial usage of the term ''WMA'', especially in marketing materials and device specifications, usually refers to this codec only. The first version of the codec released in 1999 is regarded as WMA 1. In the same year, the Bit Stream syntax, or Compression Algorithm , was altered in minor ways and became WMA 2. Since then, newer versions of the codec were released, but the algorithm has remained the same. This maintained compatibility between codec versions. WMA is a Lossy audio codec based on the study of Psychoacoustics . Audio signals which are deemed to be imperceptable to the human ear may be discarded during the compression process. This results in a loss of audio quality and may introduce undesired Compression Artifacts not present in the source material. |
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