Editing Windows Media Audio (section)

==Codecs==
Each WMA file features a single audio track in one of the four sub-formats: WMA, WMA Pro, WMA Lossless, or WMA Voice. These formats are implemented differently from one another, such that they are technically distinct and mutually incompatible; that is to say, a device or software compatible with one sub-format does not therefore automatically support any of the other codecs. Each codec is further explained below.

===Windows Media Audio===
'''Windows Media Audio''' (WMA) is the most common codec of the four WMA codecs. The 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.<ref name="Broadcom"/> Since then, newer versions of the codec have been released, but the decoding process remained the same, ensuring compatibility between codec versions.<ref name="Broadcom"/> WMA is a lossy audio codec based on the study of [[psychoacoustics]]. Audio signals that are deemed to be imperceptible to the human ear are encoded with reduced resolution during the compression process.

WMA can encode audio signals sampled at up to 48&nbsp;[[kHz]] with up to two discrete channels ([[stereo]]). WMA 9 introduced [[variable bit rate]] (VBR) and [[average bit rate]] (ABR) coding techniques into the MS encoder although both were technically supported by the original format.<ref name="Broadcom"/> WMA 9.1 also added support for low-delay audio,<ref name="Low-Delay Audio">{{cite web |url=http://msdn2.microsoft.com/en-us/library/aa390496.aspx |title=Windows Media Format 11 SDK Low-Delay Audio |publisher=Microsoft MSDN |access-date=2007-08-16 |url-status=live |archive-url=https://web.archive.org/web/20071024183517/http://msdn2.microsoft.com/en-us/library/aa390496.aspx |archive-date=2007-10-24 }}</ref> which reduces [[Latency (engineering)|latency]] for encoding and decoding.

Fundamentally, WMA is a transform coder based on [[modified discrete cosine transform]] (MDCT), somewhat similar to [[Advanced Audio Coding|AAC]], [[Cook Codec|Cook]] and [[Vorbis]]. The bit stream of WMA is composed of superframes, each containing 1 or more frames of 2048 samples. If the bit reservoir is not used, a frame is equal to a superframe. Each frame contains several blocks, which are 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 coding|huffman coded]]. Stereo information is typically [[Joint stereo#M/S stereo coding|mid/side]] coded. At low bit rates, [[line spectral pairs]] (typically less than 17&nbsp;kbit/s) and a form of noise coding (typically less than 33&nbsp;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, 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 Pro extends this by adding a 6th block size used at 88.2/96&nbsp;kHz sampling rate.

Certified [[PlaysForSure]] devices, as well as a large number of uncertified devices, ranging from portable hand-held music players to set-top [[DVD player]]s, 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.<ref name="nokia">{{cite web|url=http://www.microsoft.com/presspass/press/2005/feb05/02-14NokiaCollaborationPR.mspx|title=Microsoft and Nokia Collaborate to Help Ensure Consumers Can Enjoy Digital Music Anywhere|website=[[Microsoft]]|url-status=dead|archive-url=https://web.archive.org/web/20070831104239/http://www.microsoft.com/presspass/press/2005/feb05/02-14NokiaCollaborationPR.mspx|archive-date=2007-08-31|access-date=2007-08-15}}</ref> 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.<ref name="PSP Review">{{cite web |author=Carnoy, David |title=Sony PSP review |date=2005-03-23 |url=http://reviews.cnet.co.uk/gamesconsoles/0,139102149,39188324,00.htm |access-date=2007-08-16 |url-status=dead |archive-url=https://web.archive.org/web/20070810200119/http://reviews.cnet.co.uk/gamesconsoles/0,139102149,39188324,00.htm |archive-date=2007-08-10 }}</ref>

===Windows Media Audio Professional===
[[Image:WMA10ProOptions.PNG|thumb|Screenshot of Windows Media Encoder 9 Series, displaying new encoding options for Windows Media Audio 10 Professional.]]
'''Windows Media Audio Professional''' (WMA Pro) is an improved lossy codec closely related to WMA standards. It retains most of the same general coding features, but also features improved entropy coding and quantization strategies as well as more efficient stereo coding. Notably, many of the WMA standard's low bitrate features have been removed, as the core codec is designed for efficient coding at most bitrates. Its main competitors include [[Advanced Audio Coding|AAC]], [[HE-AAC]], [[Vorbis]], Dolby Digital, and DTS. It supports 16-bit and 24-bit sample bit depth, sampling rates up to 96&nbsp;kHz, and up to eight discrete channels ([[7.1|7.1 channel surround]]).<ref name="Windows Media Audio 9 Professional">{{cite web |url=http://www.microsoft.com/windows/windowsmedia/forpros/codecs/audio.aspx#WindowsMediaAudio9Professional |title=Windows Media Audio Codecs: Windows Media Audio 9 Professional |publisher=Microsoft |access-date=2007-08-16 |url-status=live |archive-url=https://web.archive.org/web/20070901193343/http://www.microsoft.com/windows/windowsmedia/forpros/codecs/audio.aspx#WindowsMediaAudio9Professional |archive-date=2007-09-01 }}</ref> 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 could theoretically go beyond 7.1 surround sound and support "an unlimited number of channels"; however, Microsoft chose to limit its current capability to eight (7.1 discrete channels).<ref name="winsupersite">{{cite web|url=http://www.winsupersite.com/reviews/wm9series.asp|title=Paul Thurrott's SuperSite for Windows: Windows Media 9 Series reviewed|url-status=dead|archive-url=https://web.archive.org/web/20070528090443/http://www.winsupersite.com/reviews/wm9series.asp|archive-date=2007-05-28|access-date=2007-06-24}}</ref>

The codec's bit stream syntax was frozen at the first version, WMA 9 Pro.<ref name="wmav9series">{{cite web|url=http://download.microsoft.com/download/6/f/c/6fc03c60-5d5b-42c0-bcce-5e184fa56741/2_Audio_Video.ppt|title=Windows Media Audio & Video 9 Series|url-status=dead|archive-url=https://web.archive.org/web/20070928022926/http://download.microsoft.com/download/6/f/c/6fc03c60-5d5b-42c0-bcce-5e184fa56741/2_Audio_Video.ppt|archive-date=2007-09-28|access-date=2007-08-08}}</ref> Later versions of WMA Pro introduced low-bit rate encoding, low-delay audio,<ref name="wmalowdelay">{{cite web|url=http://msdn2.microsoft.com/en-us/library/aa390496.aspx|title=Low-Delay Audio|website=msdn2.microsoft.com|access-date=30 April 2018|url-status=live|archive-url=https://web.archive.org/web/20080417175047/http://msdn2.microsoft.com/en-us/library/aa390496.aspx|archive-date=17 April 2008}}</ref> frequency interpolation mode,<ref name="streamingmedia.com Windows Media Best Practices">{{cite web |author=Smith, Tony |title=Best Practices for Windows Media Encoding |date=2007-02-21 |url=http://www.streamingmedia.com/article.asp?id=9510&page=2&c=4 |access-date=2007-08-16 |archive-url=https://web.archive.org/web/20070831100606/http://www.streamingmedia.com/article.asp?id=9510&page=2&c=4 |archive-date=2007-08-31 |url-status=dead }}</ref> and an expanded range of [[sampling rate]] and [[Audio bit depth|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.<ref name="edn">{{cite web|url=http://www.edn.com/index.asp?layout=article&articleid=CA6391444&industryid=22043|title=Voices: Microsoft's Amir Majidimehr: a window to the world of digital media - 11-23-2006 - EDN|url-status=dead|archive-url=https://web.archive.org/web/20070430153905/http://www.edn.com/index.asp?layout=article&articleid=CA6391444&industryid=22043|archive-date=2007-04-30|access-date=2007-06-07}}</ref> 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&nbsp;kbit/s, and tracks can be encoded at the native audio CD resolution (44.1&nbsp;kHz, 16-bit), previously the domain of WMA Standard.

Despite a growing number of supported devices and its superiority over WMA, WMA Pro still has little hardware and software support. Some notable exceptions to this are the [[Microsoft Zune]] (limited to stereo),<ref name="zunefaq">{{cite web|url=http://www.zune.net/en-us/support/howto/start/providecontent.htm|title=Zune.net: How-To - Provide Content for Zune|url-status=live|archive-url=https://web.archive.org/web/20070819115547/http://www.zune.net/en-us/support/howto/start/providecontent.htm|archive-date=2007-08-19}}</ref> [[Xbox 360]],<ref name="xboxfaq">{{cite web|url=http://blogs.msdn.com/xboxteam/default.aspx|title=Spring '07 Video Playback FAQ|url-status=dead|archive-url=https://web.archive.org/web/20080213124920/http://blogs.msdn.com/xboxteam/default.aspx|archive-date=2008-02-13|access-date=2007-08-08}}</ref> [[Windows Mobile]]-powered devices with Windows Media Player 10 Mobile,<ref name="winmobilefaq">{{cite web|url=http://www.microsoft.com/windows/windowsmedia/player/windowsmobile/faq.aspx|title=Windows Media Player Mobile FAQ|website=[[Microsoft]]|url-status=live|archive-url=https://web.archive.org/web/20070914112132/http://www.microsoft.com/windows/windowsmedia/player/windowsmobile/faq.aspx|archive-date=2007-09-14}}</ref> newer [[Gigabeat|Toshiba Gigabeat]] and [[Motorola]] devices,<ref name="msmotorolawmapro">{{cite web|url=http://www.microsoft.com/presspass/press/2006/feb06/02-13MotorolaMSCollabPR.mspx|title=Motorola and Microsoft Plan to Bring More Choice to Mobile Music Fans|website=[[Microsoft]]|url-status=dead|archive-url=https://web.archive.org/web/20071024172933/http://www.microsoft.com/presspass/press/2006/feb06/02-13MotorolaMSCollabPR.mspx|archive-date=2007-10-24|access-date=2018-12-06}}</ref><ref name="digitallifestyles">{{cite web|url=http://digital-lifestyles.info/2006/02/13/motorola-dis-apple-expect-more-microsoft-music-phones-3gsm/|title=Motorola Dis Apple, Expect More Microsoft Music Phones: 3GSM|url-status=dead|archive-url=https://web.archive.org/web/20070927230600/http://digital-lifestyles.info/2006/02/13/motorola-dis-apple-expect-more-microsoft-music-phones-3gsm/|archive-date=2007-09-27|access-date=2007-08-08}}</ref> and devices running recent versions of the [[Rockbox]] alternative firmware.<ref name="rockbox">{{cite web |title=New WMA Audio Codecs |url=https://www.rockbox.org/wiki/NewWMAAudioCodecs |url-status=live |archive-url=https://web.archive.org/web/20110106054756/https://www.rockbox.org/wiki/NewWMAAudioCodecs |archive-date=2011-01-06}}</ref> In addition, WMA Pro is a requirement for the [[WMV HD]] certification program.<ref name="wmvhd">{{Cite web|url=https://www.bing.com/?form=HPFBBK&ssd=20230121_0800&mkt=en-ID|title=Info|website=Bing}}</ref> On the software side, [[Verizon]] utilizes WMA 10 Pro for its V CAST Music Service,<ref name="verizonwmapro">{{cite web|url=http://www.microsoft.com/presspass/press/2006/jan06/01-05WMVCASTPR.mspx|title=Verizon Wireless Chooses Microsoft Windows Media to Power Its New V CAST Music Service|website=[[Microsoft]]|url-status=dead|archive-url=https://web.archive.org/web/20070615201708/http://www.microsoft.com/presspass/press/2006/jan06/01-05WMVCASTPR.mspx|archive-date=2007-06-15|access-date=2018-12-06}}</ref> and [[Windows Media Player|Windows Media Player 11]] has promoted the codec as an alternative to WMA for copying audio CD tracks.<ref name="winvistawmp11">{{cite web|url=http://www.microsoft.com/windows/products/windowsvista/features/details/mediaplayer11.mspx|title=Windows Vista Features Explained Windows Media Player 11|website=[[Microsoft]]|url-status=live|archive-url=https://web.archive.org/web/20070913180242/http://www.microsoft.com/windows/products/windowsvista/features/details/mediaplayer11.mspx|archive-date=2007-09-13}}</ref> WMA Pro is supported in Silverlight as of version 2 (though only in stereo mode). In the absence of the appropriate audio hardware, WMA Pro can automatically [[Downmixing|downmix]] multichannel audio to stereo or [[Monophonic sound|mono]], and 24-bit resolution to 16-bit during playback.

A notable example of WMA Pro being used instead of WMA Standard is the NBC Olympics website which uses WMA 10 Pro in its low-bitrate mode at 48 kbit/s.{{Citation needed|date=April 2021}}

===Windows Media Audio Lossless===
[[File:5 1 channels (surround sound) label.svg|thumb|Label for 5.1 surround sound, the maximum channels supported in the format.]]

As part of the Windows Media 9 series, Microsoft introduced '''Windows Media Audio Lossless''' in early 2003, a [[Data compression#Audio|lossless]] audio format sharing the .wma file extension as its lossy counterparts. It is designed to store a digital audio stream (such as a [[Compact Disc Digital Audio|CD-Audio]] track) at some fraction of the original. Each sample in a channel can be encoded at up to 24 bits, at a rate of 96 KHz, with up to 6 discrete channels (for [[5.1 surround sound]]). The container is also said to have dynamic range compression control. Like WMA Pro, the WMA Lossless decoder can perform downmixing when capable audio hardware is not present.{{Citation needed|date=May 2010}} While the details of the format have never been publicly documented, it has been reverse-engineered for use on non-Microsoft platforms by the open source [[FFmpeg]] project. Only 16-bit WMA files are supported as of 2012.{{needs update|date=May 2025}}

Designed for archival purposes,<ref name="Windows Media Audio 9 Lossless">{{cite web |url=http://www.microsoft.com/windows/windowsmedia/forpros/codecs/audio.aspx#WindowsMediaAudio9Lossless |title=Windows Media Audio Codecs: Windows Media Audio 9 Lossless |publisher=Microsoft |access-date=2007-08-16 |url-status=live |archive-url=https://web.archive.org/web/20070901193343/http://www.microsoft.com/windows/windowsmedia/forpros/codecs/audio.aspx#WindowsMediaAudio9Lossless |archive-date=2007-09-01 }}</ref> it competed with [[ATRAC]] Advanced Lossless, [[Dolby TrueHD]], [[DTS-HD Master Audio]], [[Shorten (file format)|Shorten]], [[Monkey's Audio]], [[FLAC]], [[Apple Lossless]], and [[WavPack]]. Since late 2011,<ref name=Apache-license>{{cite web|url=http://alac.macosforge.org|title=Welcome to the Apple Lossless Audio Codec Project|work=Apple Lossless Audio Codec|publisher=MacOS Forge|date=October 27, 2011|access-date=October 29, 2011|url-status=live|archive-url=http://archive.wikiwix.com/cache/20160615225151/http://alac.macosforge.org/|archive-date=June 15, 2016}}</ref><ref name=Apache-ars>{{cite web|last=Foresman|first=Chris|title=After seven years, Apple open sources its Apple Lossless Audio Codec|url=https://arstechnica.com/apple/news/2011/10/after-seven-years-apple-open-sources-its-apple-lossless-audio-codec.ars|website=Ars Technica|date=October 28, 2011|access-date=October 29, 2011|url-status=live|archive-url=https://web.archive.org/web/20111029123807/http://arstechnica.com/apple/news/2011/10/after-seven-years-apple-open-sources-its-apple-lossless-audio-codec.ars|archive-date=October 29, 2011}}</ref><ref name=Apache-3>{{cite web|url=http://h-online.com/-1368212|archive-url=https://web.archive.org/web/20120515214941/http://www.h-online.com/open/news/item/Apple-open-sources-its-ALAC-lossless-audio-codec-1368212.html |archive-date=15 May 2012|title=Apple open sources its ALAC lossless audio codec|first=Chris|last=von Eitzen|publisher=[[The H]]|date=October 28, 2011|access-date=October 29, 2011}}</ref> the last three have the advantage of having [[open source software|open source]] encoders, no licensing costs, and availability on nearly any [[operating system]]. The typical compression ratio for music varies between 1.7:1 and 3:1.<ref name="Windows Media Audio 9 Lossless"/><ref name="extremetech">{{cite web|url=http://www.extremetech.com/article2/0,1558,1560783,00.asp|title=ExtremeTech Audio Codec Quality Shootout|url-status=live|archive-url=https://web.archive.org/web/20110607190304/http://www.extremetech.com/article2/0,1558,1560783,00.asp|archive-date=2011-06-07}}</ref><ref>{{cite web |url=http://members.home.nl/w.speek/comparison.htm |title=Comparison of lossless audio compressors |access-date=2010-11-25 |url-status=dead |archive-url=https://web.archive.org/web/20101125045330/http://members.home.nl/w.speek/comparison.htm |archive-date=2010-11-25 }}</ref> It compresses an audio CD to a range of 206 to 411&nbsp;MB, at bit rates of 470 to 940&nbsp;kbit/s.

Like WMA Standard, WMA Lossless was adopted by a few online distribution stores in the mid-2000s.<ref name="businessweek">{{cite web|url=http://www.businessweek.com/technology/content/jun2005/tc2005062_3663_tc024.htm|title=Is This Digital Music's Future|url-status=dead|archive-url=https://web.archive.org/web/20070715011626/http://www.businessweek.com/technology/content/jun2005/tc2005062_3663_tc024.htm|archive-date=2007-07-15}}</ref><ref name="microsoftwmpstores">{{cite web|url=http://www.microsoft.com/windows/windowsmedia/player/stores.aspx|title=Online Stores in Windows Media Player|website=[[Microsoft]]|url-status=live|archive-url=https://web.archive.org/web/20070727062708/http://www.microsoft.com/windows/windowsmedia/player/stores.aspx|archive-date=2007-07-27}}</ref> Hardware support for the codec became available on the first-party [[Zune 4, 8, 16|Zune 4, 8]], [[Zune 30|30]], [[Zune 80|80, 120]] (with firmware version 2.2 or later), and [[Zune HD|HD]] portable media players and the [[Xbox 360]].<ref name="xboxfaq"/> Third-party support emerged in the Cowon A3,<ref>{{cite web|url=https://techcaption.com/what-is-windows-audio-endpoint-builder-service/ |title=What is Windows Audio Endpoint Builder service And How To Start/Stop It |website=techcaption.com |author=Tushar |date=July 2019}}</ref> Cowon S9, [[Bang & Olufsen]] Serenata,<ref>{{usurped|1=[https://web.archive.org/web/20070930231119/http://www.serenatamobile.com/ Article title]}}</ref> Sony Walkman NWZ-A and NWZ-S series, Toshiba Gigabeat S and V models, Toshiba T-400, the Meizu M3, and [[Best Buy]]-exclusive Insignia NS-DV, Pilot, and Sport music players. The Logitech Squeezebox Touch was also updated to support the format natively; previously it was added through transcoding. [[Windows Mobile]]-powered devices with Windows Media Player 10 Mobile,<ref name="winmobilefaq"/> and Windows Phone (version 8 and above) also included playback support for the format.

===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<ref>Ralph Giles of [[Xiph.org]] explained that Xbox Live uses Speex for voice compression in the June 6, 2005 interview on [[LugRadio]]: {{cite web |url=http://www.lugradio.org/episodes/29 |title=Linux radio show - LugRadio |access-date=2007-10-10 |url-status=live |archive-url=https://web.archive.org/web/20071014210527/http://lugradio.org/episodes/29 |archive-date=2007-10-14 }}</ref>), [[ACELP]], and other codecs. Designed for low-bandwidth, voice playback applications,<ref name="Windows Media Audio 9 Voice">{{cite web |url=http://www.microsoft.com/windows/windowsmedia/forpros/codecs/audio.aspx#WindowsMediaAudio9Voice |title=Windows Media Audio Codecs: Windows Media Audio 9 Voice |publisher=Microsoft |access-date=2007-08-16 |url-status=live |archive-url=https://web.archive.org/web/20070901193343/http://www.microsoft.com/windows/windowsmedia/forpros/codecs/audio.aspx#WindowsMediaAudio9Voice |archive-date=2007-09-01 }}</ref> 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.<ref name="wmav9series"/> WMA Voice supports up to 22.05&nbsp;kHz for a single channel (mono) only.<ref name="Windows Media Audio 9 Voice"/> Encoding is limited to [[constant bit rate]] (CBR) and up to 20&nbsp;kbit/s. The first and only version of the codec is WMA 9 Voice.

Windows Mobile-powered devices with Windows Media Player 10 Mobile have native support for WMA 9 Voice playback.<ref name="winmobilefaq"/> In addition, [[BBC World Service]] has employed WMA Voice for its [[Internet radio]] streaming service.<ref name="roku">{{cite web|url=http://www.rokulabs.com/products_soundbridge_internet.php|title=Roku - SoundBridge Internet Radio|url-status=dead|archive-url=https://web.archive.org/web/20070816182910/http://www.rokulabs.com/products_soundbridge_internet.php|archive-date=2007-08-16|access-date=2007-08-08}}</ref>