Extract Audio from MKV to WMA — Free Online Tool
Extract and convert audio from MKV video files to WMA format using Microsoft's wmav2 codec — ideal for Windows environments and legacy media players that expect the Windows Media Audio container. The conversion strips all video streams and transcodes the audio directly to a lossy WMA file without any server upload.
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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 container that can hold a wide variety of audio codecs — commonly AAC, Opus, Vorbis, FLAC, or MP3. Since WMA uses Microsoft's proprietary wmav2 codec, none of these source codecs are compatible with the WMA container, meaning the audio must be fully re-encoded (transcoded) rather than simply copied. FFmpeg decodes the first audio stream found in the MKV file, discards all video streams entirely using the -vn flag, then re-encodes the audio from scratch into wmav2 at the target bitrate. The result is a standalone .wma file containing only the re-encoded audio. Because this involves full transcoding from one lossy format to another (or from lossless to lossy), some generation loss is expected compared to the original source.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg program, the open-source multimedia processing engine that handles all decoding, filtering, and encoding operations in this conversion pipeline. In the browser-based version of this tool, FFmpeg runs as a WebAssembly (wasm) binary with no server involvement. |
-i input.mkv
|
Specifies the input file — in this case, a Matroska (.mkv) container, which may contain video, one or more audio tracks, subtitles, and chapter data. FFmpeg reads and demuxes all streams from this container before applying the conversion flags. |
-vn
|
Disables video output entirely, ensuring no video stream from the MKV is written to the output WMA file. Since WMA is a pure audio container, this flag is essential — without it, FFmpeg would attempt to include video and fail, because ASF/WMA has no video track support in this configuration. |
-c:a wmav2
|
Sets the audio encoder to wmav2 (Windows Media Audio version 2), Microsoft's proprietary lossy audio codec that is the standard for .wma files. Because MKV audio codecs like AAC, Opus, or FLAC are not compatible with the WMA container, a full re-encode using wmav2 is mandatory rather than a stream copy. |
-b:a 128k
|
Sets the audio bitrate to 128 kilobits per second for the wmav2 encoder, which operates in constant bitrate (CBR) mode. At 128k, the output WMA file strikes a balance between file size and perceptible audio quality, though users with audiophile requirements or high-quality source audio may prefer 256k or 320k. |
output.wma
|
Specifies the output filename with the .wma extension, which instructs FFmpeg to wrap the wmav2-encoded audio in a Microsoft ASF container — the standard packaging for WMA files. The .wma extension is recognized natively by Windows and all WMA-compatible media players. |
Common Use Cases
- Preparing audio tracks from MKV video files for playback on older Windows Media Player installations or Windows CE/Mobile devices that only support WMA natively
- Distributing audio commentary or lecture recordings (originally captured as MKV screencasts) to corporate environments where WMA is the approved audio format
- Extracting music or soundtrack audio from MKV anime or film files to populate a Windows Media Player library that organizes files by WMA metadata tags
- Converting MKV audiobook rips to WMA for use on older Microsoft Zune devices or early-generation Windows-based portable media players
- Supplying WMA audio files required by certain digital rights management (DRM) workflows or enterprise media distribution systems built on Windows Media Services
- Archiving the audio portion of large MKV recordings in a smaller, compressed WMA file to save storage while retaining compatibility with Windows-centric media infrastructure
Frequently Asked Questions
Yes, some quality loss is unavoidable in this conversion. If your MKV contains a lossy audio codec like AAC or Opus, transcoding to wmav2 introduces a second generation of lossy compression, which compounds artifacts from both encoders. If your MKV audio is lossless (e.g., FLAC), the quality loss is limited to a single encoding step, but you still end up with a lossy WMA file. To minimize degradation, use the highest bitrate WMA option available (256k or 320k), especially when the source is already lossy.
Both are permanently discarded. WMA does not support subtitles or chapter data — it is a pure audio container with no provision for those track types. The -vn flag combined with the WMA output format means FFmpeg writes only the audio stream. If you need to preserve subtitles or chapters, you should export them separately from the MKV before running this conversion.
By default, FFmpeg selects the first audio stream it encounters in the MKV file, which is typically the primary language track. WMA does not support multiple audio tracks in a single file, so only one stream can be output. If you need a specific track — for example, a director's commentary or a secondary language — you can add -map 0:a:1 (for the second audio track, zero-indexed) to the FFmpeg command before the output filename to select it explicitly.
Partially. FFmpeg will attempt to transfer standard metadata fields — such as title, artist, album, and track number — from the MKV container to the WMA file's ASF metadata tags. However, MKV supports a richer metadata schema than WMA, so fields that have no direct WMA equivalent will be dropped. You should verify the tags in a media player or tag editor after conversion if accurate metadata is important for your use case.
Replace the 128k value in the -b:a 128k flag with your preferred bitrate. For example, use -b:a 256k or -b:a 320k for higher quality output, or -b:a 64k for a smaller file at the cost of noticeable audio degradation. The full command at 256k would be: ffmpeg -i input.mkv -vn -c:a wmav2 -b:a 256k output.wma. Note that wmav2 is a CBR (constant bitrate) encoder, so the bitrate you specify is applied uniformly across the entire file.
Yes. WMA version 1 (wmav1) was designed for Windows Media Player 6.4 and earlier, and some extremely legacy hardware or software may only decode wmav1. To use it, change -c:a wmav2 to -c:a wmav1 in the command. However, wmav1 generally produces lower audio quality at the same bitrate compared to wmav2, and virtually all modern WMA-compatible devices support wmav2, so this substitution is only worth making if you have a confirmed compatibility requirement for the older codec.
The single-file command shown here processes one file at a time, but you can adapt it for batch processing in a shell script. On Linux or macOS, use: for f in *.mkv; do ffmpeg -i "$f" -vn -c:a wmav2 -b:a 128k "${f%.mkv}.wma"; done. On Windows Command Prompt, use: for %f in (*.mkv) do ffmpeg -i "%f" -vn -c:a wmav2 -b:a 128k "%~nf.wma". This is particularly useful when you have many MKV files over 1GB that exceed browser-based processing limits and need to run locally.
Technical Notes
The WMA format is built on Microsoft's Advanced Systems Format (ASF) container, which is fundamentally different from the Matroska container used by MKV. While MKV is an open standard capable of holding virtually any codec, ASF is a proprietary Microsoft format optimized for streaming and tight integration with the Windows ecosystem. The wmav2 codec used in this conversion is a CBR (constant bitrate) encoder, unlike the VBR modes available in formats such as Vorbis or AAC. This means that silence and simple audio passages are encoded at the same bitrate as complex passages, which is less efficient than modern VBR codecs. WMA files do carry ASF-format metadata tags that are readable by Windows Media Player, Windows Explorer, and most WMA-compatible media libraries, though the tag field set is narrower than MKV's. One practical limitation worth noting: WMA does not support multi-channel audio beyond stereo in the standard wmav2 profile. If your MKV source contains 5.1 or 7.1 surround audio, FFmpeg will automatically downmix it to stereo during encoding. For surround preservation, WMA Pro (wmapro) would be required, but that codec is not supported in the standard FFmpeg wmav2 encoder used here.