Windows Media Video (WMV) MIME Type
video/x-ms-wmv identifies, how WMV relates to ASF and its codecs, which applications open it, and how Poly supports WMV files. MIME type details for video/x-ms-wmv
In active use| MIME type | video/x-ms-wmv |
|---|---|
| Extensions | .wmv |
| Magic number | 30 26 B2 75 8E 66 CF 11 A6 D9 00 AA 00 62 CE 6C |
| First standardized | 1999 |
| Created by | Microsoft |
| Browser support | |
| Example applications | VLC media player, Windows Media Player |
| Poly support | Yes. Poly recognizes `.wmv` files and makes supported video content and metadata available for preview, search, and agent use. |
| Indexed by Poly | Yes. Poly indexes the filename, available technical metadata, spoken transcript, and visual content. A transcript requires usable audio. |
| Preview in Poly | Yes. Poly provides thumbnails, timeline previews, and in-app playback for supported WMV media. |
| Poly agent | Yes. The Poly agent can use supported visual content, transcript, and metadata. |
What does video/x-ms-wmv mean?
The video/x-ms-wmv media type identifies Windows Media Video files, normally with the .wmv extension. Microsoft defines that pairing for Windows Media files containing audio, video, or both.1
WMV is not one codec or a completely separate container. A .wmv file normally uses Microsoft's Advanced Systems Format (ASF) container and carries video encoded with a Windows Media Video codec. Files in the family may use WMV 7, WMV 8, WMV 9, or related profiles, so two WMV files can have different playback requirements.23
video/x-ms-wmv is a widely used conventional media type, but it is not registered in IANA's current media type registry. The x- prefix reflects that historical status.24How to identify a WMV file
ASF files begin with the 16-byte GUID for the ASF Header Object:
30 26 B2 75 8E 66 CF 11 A6 D9 00 AA 00 62 CE 6C
That signature identifies the ASF container family, not WMV by itself. Windows Media Audio and files using the broader .asf extension can begin with the same bytes. A reliable detector should validate the ASF objects and inspect the stream descriptions before deciding that a file contains video.25
ASF organizes content into objects. The required Header Object describes the streams and can hold metadata, the required Data Object stores timed packets, and optional Index Objects support seeking. The container can carry multiple video or audio streams at different bit rates.56
Renaming another video to .wmv does not convert it. Likewise, changing .wmv to .mp4 leaves the ASF structure and original codecs untouched.
WMV history and codec versions
The WMV family emerged as Microsoft moved its streaming platform to the Windows Media brand in 1999. That year's Windows Media Technologies 4.0 release highlighted updated video compression, download-and-play media, multibit-rate streaming, and rights management.7
Later generations included WMV 7, WMV 8, and WMV 9. Microsoft describes Windows Media Video 9 as its implementation of the VC-1 standard. SMPTE published VC-1 as SMPTE 421M in 2006, giving the core compression technology a formal industry specification.3
The extension still does not tell you the precise codec profile. A WMV file can also contain audio, commonly Windows Media Audio. Check both video and audio codecs when compatibility matters.
How to open a video/x-ms-wmv file
WMV is best opened with a desktop media application. Useful choices include:
- VLC media player, whose supported inputs include ASF and WMV as well as WMV 7, 8, 9, and VC-1 video.8
- Windows Media Player, which supports Windows Media files and remains a practical option on Windows.29
- A video editor or conversion tool that explicitly supports the ASF container and the codecs in the file.
Current major browsers do not provide dependable native WMV playback. MDN's current web-video guidance focuses on containers and codecs such as MP4, WebM, H.264, AV1, VP8, and VP9 rather than WMV.10 For a website, convert the video instead of relying on a browser plug-in.
Some Windows Media files use digital rights management. Microsoft notes that a player must support the relevant DRM to render protected content.1 A valid license may therefore be required even when the player understands the container and codecs.
WMV support in Poly
Poly recognizes .wmv files as video/x-ms-wmv and gives supported WMV media a useful video experience:
- Thumbnails and timeline previews for quick navigation.
- In-app playback and jumps to relevant moments.
- Available technical details such as duration, dimensions, frame rate, codecs, color information, and audio-track properties.
- Search by filename, spoken transcript, and visual content.
- Access to supported visual content, transcript, and metadata through the Poly agent.
Transcripts require a usable audio track with audible speech. Silent video can still benefit from visual search. Protected, damaged, or unsupported media may need to be opened or converted with a compatible desktop application.
See Supported File Types for the compact video feature comparison.
Converting WMV to MP4 or WebM
For modern playback and web delivery, MP4 and WebM are the usual destinations. Choose between remuxing and transcoding after inspecting the source streams.
| Goal | Practical destination | What to verify |
|---|---|---|
| Broad browser and device playback | MP4 with H.264 video and AAC audio | Video, audio, duration, synchronization, and captions |
| Open web delivery | WebM with VP9 or AV1 video and Opus audio | Playback in the browsers and devices you support |
| Preserve source quality | Keep the original WMV plus a modern derivative | Metadata, frame rate, aspect ratio, and every required stream |
| Avoid another lossy encode | Remux only when the destination accepts the existing streams | Codec compatibility with the new container |
Most WMV video is already compressed lossily. Re-encoding can discard more detail, so keep the original until you have checked the converted file from beginning to end. DRM-protected media may not be convertible without the rights and software needed to decrypt it.
WMV, ASF, WMA, and WVX are different
The Windows Media names describe related but distinct things:
| Label | Typical role | Contains media data? |
|---|---|---|
WMV / .wmv | ASF-based file containing Windows Media video | Yes |
ASF / .asf | General Advanced Systems Format container | Yes |
WMA / .wma | ASF-based file intended for Windows Media audio | Yes |
WVX / .wvx | Windows Media metafile that points to media | Usually no |
Microsoft assigns video/x-ms-wmv to .wmv, audio/x-ms-wma to .wma, and video/x-ms-wvx to .wvx metafiles.1 This distinction matters when preserving a collection: a WVX file may be only a reference, while a WMV holds the actual timed media packets.
Footnotes
- Microsoft. File Name Extensions for Windows Media. Extension, media-type, content, scripting, and DRM guidance. ↩ ↩2 ↩3
- Library of Congress. WMV (Windows Media Video) File Format. Format relationships, identifiers, codec versions, and preservation context. ↩ ↩2 ↩3 ↩4
- Microsoft. About the Windows Media Codecs. WMV 9, VC-1, profiles, and player compatibility. ↩ ↩2
- Internet Assigned Numbers Authority. Media Types Registry. The current video registry contains no
video/x-ms-wmventry. ↩ - Microsoft. Overview of the ASF Format. ASF purpose, streams, objects, metadata, and indexing. ↩ ↩2 ↩3
- Microsoft. ASF File Structure. Header, Data, and Index Object structure. ↩ ↩2
- Microsoft. Microsoft Announces Beta Release of Windows Media Technologies 4.0. Contemporary Windows Media platform announcement. ↩
- VideoLAN. VLC Features. Published container and codec support. ↩
- Microsoft. File Types Supported by Windows Media Player. ↩
- MDN Web Docs. Web Video Codec Guide. ↩