Windows Media Video

masonchung

Windows Media Video (WMV) is a generic name for the set of video codec technologies developed by Microsoft. It is part of the Microsoft Windows Media framework.
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Windows Media Video File Format
Windows Media Video File extension: .wmv
MIME type: video/x-ms-wmv
Uniform Type Identifier: com.microsoft.windows-​media-wmv
Developed by: Microsoft
Type of format: video file format

WMV (*.wmv) files use Microsoft's Advanced Systems Format (ASF) container format. These files can be played by players such as MPlayer or Windows Media Player, the latter being only available for Microsoft Windows and Macintosh systems. Many third-party players exist for various platforms such as Linux that use the FFmpeg implementation of the WMV codecs.

The extension .wmv typically describes ASF files that use Windows Media Video codecs. The audio codec used in conjunction with WM Video is typically some form of Windows Media Audio, or in rarer cases the somewhat deprecated Sipro ACELP.net audio codec. Microsoft recommends that ASF files containing non-Windows Media codecs use the more generic .asf file extension.


$ y( [7 ?4 G$ l8 W. {Windows Media Video Codecs

8 N+ Z, }& ]7 Z! a4 v( e8 n! FOverview and History
( `1 I; u) l/ q4 yThe codecs were originally developed as proprietary codecs for low-bitrate streaming applications. However, in 2003 Microsoft drafted a video codec specification based on its Windows Media Video version 9 codec and submitted it to the Society of Motion Picture and Television Engineers (SMPTE) for standardization. The standard was officially approved in March 2006 as SMPTE 421M, thus making the Windows Media Video 9 codec an open but still proprietary standard. Earlier versions of the codec (7 and 8) are considered proprietary and they fall outside the SMPTE 421M standard.
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  O3 q+ Z6 r4 d  HWMV is not built solely on Microsoft in-house technology. It is believed that WMV version 7 (WMV1) was built upon Microsoft's own non-standard version of MPEG-4 Part 2. However, as WMV version 9 has been standardized as an independent SMPTE standard (421M, also known as VC-1), it's reasonable to believe[citation needed] that WMV has sufficiently evolved in a different direction than MPEG-4 to be considered a unique codec in its own right. There are currently (April 2006) 16 companies in the VC-1 patent pool. Microsoft is also one of the members of the MPEG-4 AVC/H.264 patent pool.

The video stream is often combined with an audio stream of Windows Media Audio and encapsulated in Advanced Systems Format files, carrying the .wmv or .asf file extensions.
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; D6 R4 ?! X% r1 _WMV is generally packed into an Advanced Systems Format (ASF) container format. It can also be put into AVI or Matroska containers. The resulting files may be named .avi if it is an AVI-contained file, or .wmv or .asf if it is an ASF file, or .mkv if it is an MKV file. WMV can be stored in an AVI file when using the WMV9 VCM codec implementation. One common way to encode WMV in AVI is to use the VirtualDub encoder. Microsoft's Windows Media Player for the Mac does not support all WMV encoded files since it supports only the ASF file container. More files can be played with Flip4Mac and QuickTime or MPlayer for Mac OS X.

) x8 X$ F- @' G5 n6 s( P2 J- KWhen encapsulated in ASF file format, WMV can support DRM protected content.

. L7 ?$ \) y5 @4 ABesides being a popular codec for distributing video on the Internet[citation needed], the codec is also used to distribute high definition video on standard DVDs in a format Microsoft has branded as WMV HD. This WMV HD content can be played back on computers or compatible DVD players.
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Versions
Windows Media Video v7 (FourCC: WMV1)
Windows Media Screen v7 (FourCC: MSS1) - Optimized for low-bitrate screen captures
Windows Media Video v8 (FourCC: WMV2)
( A. K& {' l8 a( a' T: HWindows Media Video 9 (FourCC: WMV3)
Windows Media Video 9 Screen (FourCC: MSS2)
Windows Media Video 9 Advanced Profile (FourCC: WMVA) (deprecated as not VC-1 compliant)
Windows Media Video 9 Advanced Profile (FourCC: WVC1)
Windows Media Video 9 Image (FourCC: WMVP)
Windows Media Video 9.1 Image v2 (FourCC: WVP2)
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[ 本帖最後由 masonchung 於 2007-1-20 02:43 PM 編輯 ]