Windows Media Video (WMV) is the most recognized video format within the WMV family. Usage of the term WMV often refers to the Microsoft Windows Media Video codec only. Its main competitors are MPEG-4 AVC, AVS, RealVideo, and MPEG-4 ASP. The first version of the codec, WMV 7, was introduced in 1999, and was built upon Microsoft’s implementation of MPEG-4 Part 2. Continued proprietary development led to newer versions of the codec, but the bit stream syntax was not frozen until WMV 9. While all versions of WMV support variable bit rate, average bit rate, and constant bit rate, WMV 9 introduced several important features including native support for interlaced video, non-square pixels, and frame interpolation. WMV 9 also introduced a new profile titled Windows Media Video 9 Professional, which is activated automatically whenever the video resolution exceeds 300,000 pixels — e.g., 528×576, 640″480 or 768×432 and beyond — and the bitrate 1000 kbit/s. It is targeted towards high-definition video content, at resolutions such as 720p and 1080p.
The Simple and Main profile levels in WMV 9 are compliant with the same profile levels in the VC-1 specification. The Advanced Profile in VC-1 is implemented in a new WMV codec called Windows Media Video 9 Advanced Profile. It improves compressions efficiency for interlaced content and is made transport-independent, making it able to be encapsulated in an MPEG transport stream or RTP packet format. The codec is not compatible with previous WMV 9 codecs, however.
WMV is a mandatory video codec for PlaysForSure-certified online stores and devices, as well as Portable Media Center devices. The Microsoft Zune, Xbox 360, Windows Mobile-powered devices with Windows Media Player, as well as many uncertified devices, support the codec. WMV HD mandates the use of WMV 9 for its certification program, at quality levels specified by Microsoft. WMV used to be the only supported video codec for the Microsoft Silverlight platform, but H.264 codec is now also supported starting with version 3.