Free converter · Lossy re-encode
Convert WMV to MKV
Short answer
Drop your WMV file into the converter below and download the MKV file. It runs in your browser with FFmpeg, for files up to 100 MB; nothing is uploaded. The file is re-encoded to H.264 video and AAC audio in Matroska. Re-encoding takes longer than a container swap and costs some quality; how much depends on the clip and on the quality setting, and at the converter's default setting the loss can be visible, so keep the original.
Maximum file size: 100 MB. The first conversion loads a ~30 MB converter engine, once per visit. Nothing is uploaded - conversion runs on your device.
Windows Media codecs re-encoded to H.264/AAC inside MKV. · Lossy re-encode · Browser-side via FFmpeg WASM - nothing uploaded.
Key takeaways
- The 10.17 MB WMV file was re-encoded and became 3.96 MB (-61.1%).
- The result holds: Video: h264 1920x1080; Audio: aac 48000 Hz 2 ch.
- In your browser the same conversion of a 3 second clip took 29.6 seconds on the single-thread engine; natively, the 10 second clip took 5.1 seconds.
- The picture scored SSIM 0.932 against the source (1.0 would be identical).
- Next to it: WMV to AAC (-98.4%), WMV to GIF (+503%), WMV to M4A (-98.4%).
Measured: WMV to MKV
The converter's own ffmpeg arguments, run on a 10 second 1920 × 1080 excerpt of Big Buck Bunny (an animated film, not camera footage) saved in WMV. The browser column is the same arguments on the single-thread WebAssembly core with a 3 second excerpt, in a headless run; your device will differ. Results describe this clip and these encoders.
| Check | Result |
|---|---|
| Mode | Re-encoded |
| Input | WMV, 10.17 MB |
| Output | MKV, 3.96 MB (-61.1%) |
| Output streams | Video: h264 1920x1080; Audio: aac 48000 Hz 2 ch |
| Time, native, 10 s clip | 5.1 s |
| Time, browser engine, 3 s clip | 29.6 s |
| Picture similarity (SSIM) | 0.932 |
A re-encode decodes and encodes every frame or sample, so the time grows with the length of the file.
WMV vs MKV
| WMV | MKV | |
|---|---|---|
| Full name | Windows Media Video | Matroska |
| What is inside | Windows Media video and audio codecs | Almost any codec, plus several audio and subtitle tracks |
| Compression | Lossy | Depends on the codec inside |
| Best for | Old Windows Media Player content | Archiving and playback in desktop players; most social platforms do not list it |
What you get
H.264 video and AAC audio in Matroska. Windows Media codecs re-encoded to H.264/AAC inside MKV.
Where you can upload MKV
| Platform | MKV | What the platform documents |
|---|---|---|
| YouTube Shorts | Unclear | MKV is absent from YouTube's published upload-format list. |
| TikTok | Not accepted | MKV is not listed for TikTok Content Posting API uploads. |
| Instagram Reels | Not documented | MKV is not in Instagram's published video specs, which list MOV and MP4. Convert to MP4 before uploading. |
Planning a bigger file
These are estimates scaled up from the 10 second clip. Real files differ with content, resolution and bitrate, so treat them as an order of magnitude, not a promise.
| Length of the video or recording | Input size (like ours) | MKV size | Time in your browser |
|---|---|---|---|
| 1 minute | 60.49 MB | 23.53 MB | 9.9 minutes |
| 10 minutes | 604.94 MB | 235.27 MB | 99 minutes |
| 1 hour | 3629.65 MB | 1411.64 MB | 592 minutes |
A WMV file of this kind reaches the 100 MB limit of the converter after about 1.7 minutes; converting it would take roughly 17 minutes on the single-thread engine, and the MKV would be about 40.78 MB.
WMV and MKV next to their neighbors
The same clip through other conversions with the same source or the same target.
| Conversion | How | Size change | Time (native) |
|---|---|---|---|
| WMV to MKV | Re-encode | -61.1% | 5.1 s |
| WMV to AAC | Re-encode | -98.4% | 0.26 s |
| WMV to GIF | Re-encode | +503% | 7.0 s |
| WMV to M4A | Re-encode | -98.4% | 0.25 s |
| WMV to MOV | Re-encode | -61.0% | 5.4 s |
| WMV to MP3 | Re-encode | -98.4% | 0.20 s |
| WMV to MP4 | Re-encode | -61.0% | 5.5 s |
Choosing MKV
MKV: Matroska. Archiving and playback in desktop players; most social platforms do not list it. WMV: Windows Media Video. Old Windows Media Player content.
- Keep your original: a re-encode is a copy of a copy.
- If the destination states the format it accepts, use that and nothing else.
Questions people ask
Is this WMV to MKV converter free and private?
Yes. It is free, needs no account and runs entirely in your browser, so the file never leaves your device.
Will converting WMV to MKV reduce quality?
Some, because MKV is depends on the codec inside and the file is re-encoded. How much depends on the clip and on the quality setting, and at the converter's default setting the loss can be visible, so keep the original. For uploads, the platform re-encodes again anyway.
Is there a file size limit?
Files up to 100 MB. The first conversion downloads a converter engine of about 30 MB once per visit; larger files are better handled by a desktop app such as HandBrake or FFmpeg.
How do I convert WMV to MKV?
Choose the file in the converter above and download the MKV. It runs in your browser with no upload.
Will converting WMV to MKV reduce quality?
A little. The picture scored SSIM 0.932 against the source in our test.
Why did the file size change by -61.1%?
The target codec and settings decide the size. This 10 second clip came out at 3.96 MB.
How long does it take?
A 3 second clip took 29.6 seconds in the browser engine in our test; time grows with the length of the file.
How long will a WMV file of 100 MB take?
At the speed we measured in the browser engine, about 17 minutes for a file like our clip. Your device and the content will change it.
Is my file uploaded?
No. The conversion runs in your browser.
Is there a size limit?
Files up to 100 MB. The first conversion downloads a converter engine of about 30 MB once per visit.
More converters
Sources and how we checked
- MDN: Media container formats
- MDN: Web audio codec guide
- MDN: Image file type and format guide
- FFmpeg documentation: stream copy
- FFmpeg Documentation: ffmpeg (stream selection, -map, -c copy) (read 2026-10-09)
- MDN: Media container formats (read 2026-10-09)
- Blender Foundation: Big Buck Bunny (CC BY 3.0), the clip used for the measurements (read 2026-10-09)
Reviewed October 8, 2026. What the converter writes was measured with ffprobe on the same FFmpeg build your browser downloads; format descriptions follow MDN's media guides.