WMV stands for Windows Media Video -- developed and controlled by Microsoft. WMV is a generic name of Microsoft's video encoding solutions and doesn't necessarily define the technology what it uses -- since version 7 (WMV7) Microsoft has used its own flavour of MPEG-4 video encoding technology. DivX video format is originally based on hacked WMV codec.
Windows Media Format 11 adds support for HD video up to 1080P. WMF 11 runs only on Windows XP and Vista.
Additional information is available on Microsoft Windows Media page.
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