Windows Media Audio Totally Explained

Everything about Windows Media Audio totally explained

Windows Media Audio (WMA) is an audio data compression technology developed by Microsoft. The name can 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. Today it's one of the most popular codecs, together with MP3 and MPEG-4 AAC. In 2003 it came second after MP3 in terms of standalone players supporting it. WMA Pro, a newer and more advanced codec, supports multichannel and high resolution audio. A lossless codec, WMA Lossless, compresses audio data without loss of audio fidelity. According to the published article, the technology was transferred over to the Windows Media team at Microsoft. whose team worked on the project called MSAudio. The first finalized codec was at first referred as MSAudio 4.0. It was later officially released as Windows Media Audio, as part of Windows Media Technologies 4.0. Microsoft initially claimed that WMA delivers the same quality of MP3 at half the bit rate; Microsoft also claimed that WMA delivers "CD-quality" audio at 64 kbit/s. RealNetworks also challenged Microsoft's claims regarding WMA's superior audio quality compared to RealAudio. Windows Media Audio 7 in 2000, Windows Media Audio 8 in 2001, and Windows Media Audio 9 in 2003. Although earlier versions of Windows Media Player played WMA files, support for WMA file creation wasn't added until the seventh version. In 2003, Microsoft released new audio codecs which were not compatible with the original WMA codec. These codecs were Windows Media Audio 9 Professional, featuring a single audio track in one of following codecs: WMA, WMA Pro, WMA Lossless, or WMA Voice. These codecs are technically distinct and mutually incompatible. The ASF container format specifies how metadata 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. which reduces latency for encoding and decoding.
   Fundamentally, WMA is a transform coder based on modified discrete cosine transform (MDCT), somewhat similar to AAC and Vorbis. The bit stream of WMA is composed of superframes, each containing 1 or more frames of 2048 samples. If the bit reservoir isn't used, a frame is equal to a superframe. Each frame contains a number of blocks, which are 64, 128, 256, 512, 1024, or 2048 samples long after being transformed into the frequency domain via the MDCT. In the frequency domain, masking for the transformed samples is determined, and then used to requantize the samples. Finally, the floating point samples are decomposed into coefficient and exponent parts and independently huffman coded. Stereo information is typically mid/side coded. At low bit rates, line spectral pairs (typically less than 17 kbit/s) and a form of noise coding (typically less than 33 kbit/s) can also be used to improve quality.
   Like AAC and Ogg Vorbis, WMA was intended to address perceived deficiencies in the MP3 standard. Given their common design goals, it's not surprising that the three formats ended up making similar design choices. All three are pure transform codecs. Furthermore the MDCT implementation used in WMA is essentially a superset of those used in Ogg and AAC such that WMA iMDCT and windowing routines can be used to decode AAC and Ogg Vorbis almost unmodified. However, quantization and stereo coding is handled differently in each codec. The primary distinguishing trait of the WMA Standard format is its unique use of 5 different block sizes, compared to MP3, AAC, and Ogg Vorbis which each restrict files to just two sizes.
   WMA is one of the most popular audio codecs. Certified PlaysForSure devices, as well as a large number of uncertified devices, ranging from portable hand-held music players to set-top DVD players, support the playback of WMA files. Most PlaysForSure-certified online stores distribute content using this codec only. In 2005, Nokia announced its plans to support WMA playback in future Nokia handsets. In the same year, an update was made available for the PlayStation Portable (version 2.60) which allowed WMA files to be played on the device for the first time.

Windows Media Audio Professional

Windows Media Audio Professional (WMA Pro) is a newer and more advanced lossy audio codec. It is based on a new compression algorithm which isn't only superior to WMA in terms of quality, efficiency, and features, but also scales well at low bit rates. Its main competitors include AAC, HE-AAC, Vorbis, Dolby Digital, and DTS. It can support audio resolutions of up to 96 kHz and 24-bit, for up to eight discrete channels (7.1 channel surround). WMA Pro also supports dynamic range compression, which reduces the volume difference between the loudest and quietest sounds in the audio track. According to Microsoft's Amir Majidimehr, WMA Pro can technically go beyond 7.1 surround sound and support "an unlimited number of channels."
The codec's bit stream syntax was frozen at the first version, WMA 9 Pro. Later versions of WMA Pro introduced low-bit rate encoding, low-delay audio, frequency interpolation mode, and an expanded range of sampling rate and bit-depth encoding options. A WMA 10 Pro file compressed with frequency interpolation mode comprises a WMA 9 Pro track encoded at half the original sampling rate, which is then restored using a new compression algorithm. In this situation, WMA 9 Pro players which have not been updated to the WMA 10 Pro codec can only decode the lower quality WMA 9 Pro stream. Starting with WMA 10 Pro, eight channel encoding starts at 128 kbit/s, and tracks can be encoded at the native audio CD resolution (44.1 kHz, 16-bit), previously the domain of WMA Standard.
Despite a growing number of supported devices and its superiority over WMA, WMA Pro still enjoys little hardware and software support. Some notable exceptions to this are the Microsoft Zune (limited to stereo), Xbox 360, Windows Mobile-powered devices with Windows Media Player 10 Mobile, and newer Toshiba Gigabeat and Motorola devices. In addition, WMA Pro is a requirement for the WMV HD certification program. On the software side, Verizon utilizes WMA 10 Pro for its V CAST Music Service, and Windows Media Player 11 has promoted the codec as an alternative to WMA for copying audio CD tracks. However, the Microsoft Silverlight platform doesn't support WMA Pro. In the absence of the appropriate audio hardware, WMA Pro can automatically downmix multichannel audio to stereo or mono, and 24-bit resolution to 16-bit during playback.

Windows Media Audio Lossless

Windows Media Audio Lossless (WMA Lossless) is a lossless audio codec that competes with ATRAC Advanced Lossless, Dolby TrueHD, DTS-HD Master Audio, Apple Lossless, Shorten, Monkey's Audio, FLAC, and WavPack (the last two have the advantage of being open source software and available for nearly any operating system). Designed for archival purposes, it compresses audio signals without loss of quality from the original using VBR. When decompressed, the audio signal is an exact replica of the original. The first version of the codec, WMA 9 Lossless, and its revisions support up to 96 kHz, 24-bit audio for up to 6 discrete channels (5.1 channel surround) with dynamic range compression control. While Microsoft claims that it provides a compression ratio of up to 3:1 for audio CD tracks,
Hardware support for the codec is available on the Bang & Olufsen Serenata, Sony Walkman NWZ-A and NWZ-S series, Zune 4, 8, 80 and 30 (with firmware version 2.2 or later),Xbox 360, Similar to WMA Pro, WMA Lossless can perform downmixing when capable audio hardware isn't present.

Windows Media Audio Voice

Windows Media Audio Voice (WMA Voice) is a lossy audio codec that competes with Speex (used in Microsoft's own Xbox Live online service), ACELP, and other codecs. Designed for low-bandwidth, voice playback applications, it employs low-pass and high-pass filtering of sound outside the human speech frequency range to achieve higher compression efficiency than WMA. It can automatically detect sections of an audio track containing both voice and music and use the standard WMA compression algorithm instead.

Sound quality

� See codec listening test for a table of double-blind listening test results.

Microsoft claims that audio encoded with WMA sounds better than MP3 at the same bit rate; Microsoft also claims that audio encoded with WMA at lower bit rates sound better than MP3 at higher bit rates. Double blind listening tests with other lossy audio codecs have shown varying results, from failure to support Microsoft's claims about its superior quality to supremacy over other codecs. One independent test conducted in May 2004 at 128 kbit/s showed that WMA was roughly equivalent to LAME MP3; inferior to AAC and Vorbis; and superior to ATRAC3 (software version). Another test performed by ExtremeTech showed different results, however, placing WMA at the top of the list in terms of quality. On the Macintosh platform, Microsoft released a PowerPC version of Windows Media Player for Mac OS X in 2003, but further development of the software has ceased. Microsoft currently endorses the third-party Flip4Mac WMA, a QuickTime component which allows Macintosh users to play WMA files in any player that uses the QuickTime framework. Flip4Mac however doesn't currently support the Windows Media Audio Voice codec.

Encoders

Software that can export audio in WMA format include Windows Media Player, Windows Movie Maker, Microsoft Expression Encoder, RealPlayer, Adobe Premiere Pro, Adobe Audition, and Adobe Soundbooth. Microsoft Office OneNote supports encoding in all WMA codecs, and Windows Media Encoder supports all available bit rate and resolution options as well.

Digital rights management

While none of the WMA codecs themselves contain any DRM facilities, the ASF container format, in which a WMA track may be encapsulated, can. Windows Media DRM, which can be used in conjunction with WMA, supports time-limited music subscription services such as those offered by unlimited download services, including MTV's URGE, Napster, Rhapsody, Yahoo! Music Unlimited and Virgin Digital. Windows Media DRM, a component of PlaysForSure and Windows Media Connect, is supported on many modern portable audio devices and streaming media clients such as Roku, SoundBridge, Xbox 360 and Wii. Players which support the WMA format but not Windows Media DRM lists protected titles as unplayable.

Criticism

Sound quality claims

WMA has been subjected to a number of complaints. "Some audiophiles challenge Microsoft's claims regarding WMA's quality," according to a published article from EDN. At the early stages of WMA's development, a representative from RealNetworks claimed that WMA was a "clear and futile effort by Microsoft to catch up with RealAudio 8"
Microsoft has sometimes claimed that the sound quality of WMA at 64 kbit/s equals or exceeds that of MP3 at 128 kbit/s (commonly considered to be near-transparent). In a 1999 study funded by Microsoft, NSTL found that listeners preferred WMA at 64 kbit/s to MP3 at 128 kbit/s (as encoded by MusicMatch Jukebox). However, a September 2003 public listening test conducted by Roberto Amorim found that listeners preferred 128 kbit/s MP3 to 64 kbit/s WMA audio with greater than 99% confidence. This conclusion applied equally to other codecs at the same bitrate, leading him to conclude that:
It is important to note that both MP3 and WMA encoders have undergone active development and improvement for many years, so their relative quality may change over time.
A July 2007 public listening test by Sebastian Mares found that 64 kbit/s HE-AAC audio (encoded by Nero Digital) was statistically tied with 64 kbit/s WMA Pro audio, in terms of listener preference. � See also codec listening test for a table of public listening test results.

DRM

With regards to the DRM of WMA, the loss of the ability to restore licenses for WMA files in the Windows Media Player 11 wasn't positively received in an article from The Inquirer. In addition, the publisher criticized the Microsoft Zune for not supporting the standard Windows Media DRM system, rendering protected WMA files unplayable on the device.

Further Information

Get more info on 'Windows Media Audio'.

External Link Exchanges

Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:

<a href="http://windows_media_audio.totallyexplained.com">Windows Media Audio Totally Explained</a>

Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned.