MyMediaTools

Convert WebM to WMV — Free Online Tool

Convert WebM files (VP9 video, Opus audio) to WMV format using the msmpeg4 video codec and wmav2 audio codec — ideal for making web-optimized video compatible with Windows Media Player and legacy Windows-based workflows. Both the VP9 video and Opus audio streams are fully re-encoded during conversion since neither codec is natively supported by the ASF/WMV container.

FFmpeg Command

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Estimated output:

Conversion Complete!

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How It Works

WebM uses the VP9 video codec and Opus audio codec inside a Matroska-derived container — none of which are compatible with the Windows Media Video (WMV) format, which uses Microsoft's ASF container. This means the entire file must be transcoded: the VP9 video stream is decoded and re-encoded to msmpeg4 (Microsoft MPEG-4 v3), and the Opus audio stream is decoded and re-encoded to WMA v2 (wmav2). The output file is wrapped in an ASF container with the .wmv extension using the -f asf flag. Because both streams are lossy re-encodes, some generation loss is unavoidable — the final WMV file will not be a lossless reproduction of the original WebM. Any transparency, subtitle tracks, or chapter markers present in the WebM will be dropped, as the WMV/ASF format does not support these features.

What Each Flag Does

Flag What it does
ffmpeg Invokes the FFmpeg command-line tool, which handles all decoding, re-encoding, and container muxing for this conversion from WebM to WMV.
-i input.webm Specifies the input WebM file containing VP9 video and Opus audio streams inside a Matroska-derived container.
-c:v msmpeg4 Re-encodes the VP9 video stream to Microsoft MPEG-4 Version 3 (msmpeg4), the default and most compatible video codec for WMV/ASF output — required since VP9 is not supported by the ASF container.
-c:a wmav2 Re-encodes the Opus audio stream to Windows Media Audio v2 (wmav2), Microsoft's standard lossy audio codec for WMV files, replacing the Opus codec which is incompatible with the ASF container.
-b:v 2000k Sets the video bitrate to 2000 kilobits per second for the msmpeg4 encoder; unlike the source WebM's VP9 codec, msmpeg4 uses bitrate-based (CBR/VBR) quality control rather than a CRF quality scale.
-b:a 128k Sets the wmav2 audio output bitrate to 128 kilobits per second, providing a balance between audio fidelity and file size appropriate for most speech and music content.
-f asf Explicitly forces FFmpeg to use the ASF (Advanced Systems Format) container muxer, which is the underlying container format for all WMV files — necessary because FFmpeg references this container as 'asf' internally rather than 'wmv'.
output.wmv Specifies the output filename with the .wmv extension, producing a Windows Media Video file playable in Windows Media Player and compatible with Windows-based legacy media workflows.

Common Use Cases

  • Preparing web-sourced WebM video downloads for playback on Windows XP or Windows 7 machines where modern codecs or browsers are unavailable
  • Submitting video content to corporate intranet systems or legacy media servers that only accept WMV or ASF-format files
  • Converting HTML5 web video exports from screen recorders or design tools into a format compatible with Windows Media Player for client presentations
  • Archiving WebM video from browser-based platforms into a format accepted by older Windows-based video editing software that lacks VP9 support
  • Packaging VP9-encoded tutorial videos as WMV files for distribution on CD-ROMs or USB drives intended for Windows-only audiences
  • Adapting WebM video assets for use in legacy Microsoft PowerPoint presentations that rely on Windows Media Player for embedded video playback

Frequently Asked Questions

Yes, some quality loss is inevitable in this conversion. The original WebM uses VP9 and Opus, both of which are modern, highly efficient lossy codecs. Re-encoding those streams to msmpeg4 and wmav2 — both older, less efficient codecs — at equivalent bitrates will produce a perceptibly softer or more compressed result. To minimize quality loss, increase the video bitrate using -b:v (e.g., 4000k or 6000k) and the audio bitrate using -b:a (e.g., 192k or 256k) in the FFmpeg command.
No. The ASF container used by WMV does not support video transparency (alpha channel), embedded subtitle tracks, or chapter markers. If your WebM file contains any of these features — such as VP9 alpha video or WebVTT subtitles — they will be silently dropped during conversion. If subtitle preservation is important, you should either burn the subtitles into the video using a filter (-vf subtitles) or convert to a format like MP4 or MKV instead.
WMV files are actually ASF (Advanced Systems Format) containers with a .wmv extension. FFmpeg uses the format name 'asf' internally to refer to this container type. The -f asf flag explicitly tells FFmpeg to use the ASF muxer regardless of the output filename extension, ensuring correct container structure. Without it, FFmpeg might not correctly recognize the intended output format from the .wmv extension alone in all configurations.
WMV/msmpeg4 uses bitrate-based quality control rather than a CRF scale. Adjust the -b:v flag to increase or decrease video quality: for example, use -b:v 4000k for higher quality or -b:v 1000k for a smaller file. Similarly, change -b:a 128k to a higher value like -b:a 192k for better audio. Unlike the source WebM's VP9 encoder, msmpeg4 does not support constant-quality (CRF) encoding, so bitrate is the primary lever available.
Yes. On Windows, you can use a simple batch script: 'for %f in (*.webm) do ffmpeg -i "%f" -c:v msmpeg4 -c:a wmav2 -b:v 2000k -b:a 128k -f asf "%~nf.wmv"'. On Linux or macOS, use: 'for f in *.webm; do ffmpeg -i "$f" -c:v msmpeg4 -c:a wmav2 -b:v 2000k -b:a 128k -f asf "${f%.webm}.wmv"; done'. This is particularly useful since the browser-based tool processes one file at a time and is limited to 1GB.
No. Despite the similar name, msmpeg4 (Microsoft MPEG-4 v3) is a proprietary Microsoft codec developed in the late 1990s and is not compatible with standard MPEG-4 Part 2 or H.264. It predates both and produces lower quality at equivalent bitrates. It is specifically designed for compatibility with the Windows Media ecosystem — particularly Windows Media Player — rather than for general-purpose video use. If your goal is broad compatibility rather than Windows-specific playback, an MP4 container with H.264 video would be a better choice.

Technical Notes

The WebM-to-WMV conversion involves a full transcode of both streams, with no opportunity for stream copying (remuxing) since the codec sets are entirely incompatible. The msmpeg4 codec in FFmpeg corresponds to Microsoft MPEG-4 Version 3, a closed, proprietary codec originally used in early Windows Media Video releases; it is distinct from both msmpeg4v2 (Version 2) and the later WMV9/VC-1 codec used in modern WMV files. The default video bitrate of 2000k is adequate for standard-definition content but may be insufficient for 1080p or higher-resolution WebM sources — consider 4000k–8000k for HD material. The wmav2 audio codec is a solid choice for WMV audio and is universally supported by Windows Media Player across all versions. One notable limitation: if your WebM source was encoded with HDR metadata (common with VP9 Profile 2), that metadata will be lost entirely during re-encoding to msmpeg4, which has no HDR support. Multiple audio tracks present in the WebM are technically supported by the ASF container, but practical playback support in Windows Media Player for secondary tracks is inconsistent. The -f asf flag is required because the ASF muxer must be specified explicitly — the .wmv output extension alone is not reliably sufficient for FFmpeg to select the correct container muxer.

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