Convert MKV to WMV — Free Online Tool
Convert MKV files to WMV using Microsoft's MPEG-4 video codec (msmpeg4) and WMA audio (wmav2), packaged in the ASF container that Windows Media Player and legacy Windows applications expect. This conversion trades MKV's flexible, open-standard container for Windows-native compatibility, making it ideal when you need files that work reliably in older Windows environments or Windows Media Player without additional codec packs.
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FFmpeg Command
Copy this command to run the same conversion locally with FFmpeg on your desktop. Download FFmpeg
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Note: Browser-based encoding uses approximate quality targets. For precise CRF compression, copy the FFmpeg command above and run it on your desktop.
Estimated output:
Conversion Complete!
DownloadHow It Works
MKV is a flexible open container that can hold nearly any codec, while WMV is Microsoft's proprietary format built on the Advanced Systems Format (ASF) container. During this conversion, the video stream is re-encoded from whatever codec your MKV uses (commonly H.264 or H.265) into Microsoft's MPEG-4 variant (msmpeg4), which is a lossy process that discards the original video data and rebuilds it at the target bitrate of 2000k. The audio is similarly transcoded from its original format (AAC, Opus, or others common in MKV) into Windows Media Audio v2 (wmav2). Because ASF does not support subtitle tracks or chapter markers, any subtitles or chapter data embedded in your MKV will be dropped during conversion. The special '-f asf' flag explicitly tells FFmpeg to use the ASF container muxer rather than inferring it from the file extension alone, ensuring correct file structure for Windows Media Player compatibility.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg binary — the underlying engine that performs all media processing. In this browser-based tool, it runs as a WebAssembly build (FFmpeg.wasm) entirely within your browser, but the command shown is identical to what you would run in a terminal on Windows, macOS, or Linux for local processing of files over 1GB. |
-i input.mkv
|
Specifies the input file — your Matroska (.mkv) source. FFmpeg reads the MKV container and demuxes its video, audio, subtitle, and chapter streams, making them available for re-encoding or remuxing into the WMV/ASF output. |
-c:v msmpeg4
|
Sets the video encoder to Microsoft's MPEG-4 variant (msmpeg4), the codec natively associated with WMV files and the ASF container. This re-encodes the video from whatever codec the source MKV used (such as H.264 or H.265) into the msmpeg4 format expected by Windows Media Player. |
-c:a wmav2
|
Sets the audio encoder to Windows Media Audio version 2 (wmav2), Microsoft's proprietary lossy audio codec that is the standard audio format inside WMV files. This transcodes the source audio — whether it was AAC, Opus, Vorbis, or MP3 in the MKV — into WMA for maximum compatibility with Windows Media Player and ASF-aware applications. |
-b:v 2000k
|
Targets a video bitrate of 2000 kilobits per second for the msmpeg4 encoder. Because msmpeg4 does not support CRF quality-based encoding, this CBR-style bitrate setting directly controls output quality and file size — higher values produce better-looking video but larger WMV files. |
-b:a 128k
|
Targets an audio bitrate of 128 kilobits per second for the wmav2 encoder. This is a standard quality level for WMA audio that balances file size with acceptable fidelity for speech and general music content; increase to 192k or 256k if audio quality is a priority. |
-f asf
|
Explicitly forces the output container format to ASF (Advanced Systems Format), the Microsoft container that underpins all WMV files. This flag is necessary because FFmpeg may not reliably detect the correct muxer from the .wmv extension alone, and without it the output file could be malformed or unplayable in Windows Media Player. |
output.wmv
|
The filename for the converted output file. The .wmv extension identifies this as a Windows Media Video file to the operating system and media players, and in combination with the -f asf flag, ensures the file is both correctly structured internally and correctly recognized externally. |
Common Use Cases
- Sharing video files with colleagues or clients who use older Windows systems where Windows Media Player is the default player and MKV files fail to open without third-party codec packs
- Uploading video to legacy corporate intranet portals or content management systems built on Microsoft infrastructure that accept WMV but not MKV
- Preparing video content for embedding in older Microsoft Office PowerPoint presentations, which have historically had better native support for WMV than MKV
- Converting MKV recordings for playback on older Windows Media Center setups or embedded Windows devices that do not support modern containers
- Archiving or delivering video to clients in industries (legal, government, education) that mandate WMV as a submission format for digital evidence or training materials
- Reducing a complex multi-track MKV (with multiple audio streams and subtitles) to a simplified single-stream WMV for straightforward Windows-compatible distribution
Frequently Asked Questions
No — the ASF container that underpins the WMV format does not support subtitle tracks or chapter markers, so both will be permanently stripped during this conversion. If your MKV contains subtitles that are essential to the viewer, you should either burn them into the video image using a subtitle filter before converting, or distribute the SRT/ASS subtitle file separately alongside the WMV output.
The msmpeg4 codec used in WMV output does not support constant-rate-factor (CRF) encoding, which is the quality-based variable bitrate mode available to x264 and x265. Instead, msmpeg4 uses constant bitrate (CBR) or average bitrate targeting, controlled by the -b:v flag. This means you specify a target data rate (default 2000k) rather than a target quality level, so the encoder will hit that bitrate regardless of scene complexity — complex scenes may look worse than they would under CRF encoding at equivalent file sizes.
WMV via the ASF container technically supports multiple audio tracks, but FFmpeg's default behavior will select only the first (or best-ranked) audio stream from your MKV for inclusion in the output. If you need a specific audio track — for example, a different language track — you can modify the command by adding '-map 0:v:0 -map 0:a:2' before the output filename, replacing '2' with the zero-indexed number of the audio stream you want.
File size in the WMV output is determined primarily by the -b:v 2000k setting, which targets approximately 2 megabits per second for video, plus 128k for audio. An MKV encoded with H.265 at high quality could actually be significantly smaller than the resulting WMV, since H.265 achieves better compression than msmpeg4 at equivalent visual quality. Conversely, a high-bitrate MKV with an 8000k+ video stream will produce a smaller WMV at the 2000k default. Adjust -b:v upward (e.g., 4000k or 6000k) if the output looks blocky or visually degraded.
Replace the value after -b:v with your desired bitrate. For example, changing '-b:v 2000k' to '-b:v 4000k' doubles the video data rate, producing better image quality at the cost of a larger file. For audio, change '-b:a 128k' to '-b:a 192k' or '-b:a 256k' for higher fidelity WMA audio. Keep in mind that msmpeg4 is an older codec and increasing bitrate beyond 6000k yields diminishing returns compared to modern codecs — if quality is critical, consider whether WMV is the right output format for your use case.
FFmpeg normally infers the output container from the file extension, but WMV and ASF share the same underlying container format and FFmpeg's extension detection can behave inconsistently with these Microsoft formats. Explicitly passing '-f asf' forces FFmpeg to use the ASF muxer regardless of filename, ensuring the file structure is correctly formed for Windows Media Player and other WMV-compatible applications. Without this flag, FFmpeg might fail or produce a malformed file depending on the version being used.
Technical Notes
The msmpeg4 codec used in this conversion is Microsoft's proprietary implementation of the MPEG-4 Part 2 video standard, distinct from the open-source libxvid or FFmpeg's own mpeg4 encoder. It is an older, less efficient codec than the H.264 or H.265 typically found in modern MKV files — you should expect noticeably larger file sizes or lower visual quality compared to the source at equivalent bitrates. The wmav2 audio codec is Windows Media Audio version 2, a lossy format that performs comparably to MP3 at the same bitrates but with better integration into the ASF container and Windows Media Player DRM infrastructure. Metadata such as title, artist, and copyright fields from the MKV's Matroska metadata may not transfer cleanly to ASF metadata tags, as the two systems use different tagging schemas; critical metadata should be verified and re-entered after conversion. If your source MKV contains HDR (high dynamic range) video with BT.2020 color primaries, the msmpeg4 encoder does not support HDR passthrough and will produce SDR output with potential color shift — you may want to apply a tone-mapping filter for best results.