WebM to MKV Converter
Convert WebM to MKV online for free: nothing to install, no watermark, files encrypted in transit and deleted automatically after conversion.
Advanced options
Drag & drop your WEBM file here, or
How to convert WebM to MKV in 3 steps
- 1
Upload your WebM file
Drag and drop or select the WebM file you want to convert.
- 2
Choose MKV as output
The output format is pre-selected for you — just confirm and start the conversion.
- 3
Download your file
Once processing finishes, download your converted MKV file instantly.
WebM vs MKV: what is the difference?
| WebM | MKV | |
|---|---|---|
| Full name | WebM | Matroska Video |
| Type | Video container | Video container |
| Compression | Lossy | Depends on the codec |
| Developed by | Matroska.org | |
| File extension | .webm | .mkv |
What is WebM?
WebM is an open, royalty-free video format backed by Google and designed for the web. It uses VP8, VP9 or AV1 video with Opus or Vorbis audio, plays natively in modern browsers and keeps files small, though some editors and Apple devices handle it poorly.
What is MKV?
MKV (Matroska) is an open, royalty-free container that can hold any number of video, audio and subtitle tracks plus chapters in a single file. It is popular for films and archives, but many phones, TVs and editors do not open it natively.
Tips for converting WebM to MKV
- Check the length and resolution of your WebM file first: long 4K videos take several minutes to process and may exceed the 50MB free limit.
- If you only need the soundtrack, pick an audio format such as MP3 instead of MKV — the file will be much smaller.
- Keep the original video until you have checked the converted file plays correctly on the device you want to use.
- Subtitles and extra audio tracks are not always carried over between containers, so check them after converting.
Frequently asked questions
- How do I convert WebM to MKV online?
- Upload your WebM file above, select MKV as the output format, and click Convert. ConvertFastHub processes the file in the cloud and gives you a download link — no software installation required.
- Is it free to convert WebM to MKV?
- Yes. Free accounts get 10 conversions every 24 hours with files up to 50MB. For unlimited conversions, larger files up to 1.5GB, and priority processing, upgrade to ConvertFastHub Pro.
- Is my file safe when I convert it?
- Files travel over an encrypted connection, are scanned automatically for malware (files up to 200 MB), are processed in an isolated worker and are deleted automatically: after 1 hour without an account, 24 hours with a free account, or 7 days with Pro.
- Can I convert WebM to MKV on my phone?
- Yes. The converter runs in the browser and the work happens on our servers, so it works the same on Android, iPhone, tablets and computers — there is no app to install.
- Do I need an account?
- No. You can convert without signing up; results are then kept for 1 hour. A free account keeps them for 24 hours and shows your conversion history.