WMV - technical definition

(Windows Media Video) A family of digital video compression technologies from Microsoft based on MPEG-4. Version 9 of the WMV codec was released to the SMPTE organization and became the SMPTE 421M standard, otherwise known as VC-1 (see VC-1).

WMV codec numbers and version numbers are not in sync. The first WMV (WMV1) was version 7 (WMV v7); the second (WMV2) was version 8 (WMV v8), and WMV3 was WMV v9. See Windows Media formats and WMV HD.