How to convert WebM to MKV
- Click Choose files or drop your WebM video into the box above.
- Keep the default quality, or choose a target size, resolution or frame rate.
- Click Convert and download the MKV when it is ready.
WebM vs MKV
| WebM | MKV | |
|---|---|---|
| Usual codecs | VP8, VP9 or AV1 video with Opus or Vorbis audio | Almost anything: H.264, HEVC, AV1, VP9 video; AAC, AC-3, DTS, Opus, FLAC audio; multiple subtitle and audio tracks |
| Plays on | Chrome, Firefox, Edge and Android; partial support on iPhone and Mac; not accepted by many editors | VLC, Plex, Kodi and most PCs; not supported by iPhone, iPad, QuickTime, many video editors and most websites |
| Best for | Video embedded in websites and screen recordings | Movies and TV episodes with several audio and subtitle tracks |
| Introduced | 2010 by Google | 2002 by the Matroska open-source project |
About WebM and MKV
What is WebM?
WebM is an open, royalty-free video format designed for the web. Screen recorders and browsers often save clips as WebM. It is efficient, but many video editors, iPhones, smart TVs and upload forms do not handle it well, so WebM files are frequently converted to MP4.
- Royalty-free and efficient
- Plays in Chrome, Firefox and Edge
- Weak support in editors, TVs and some Apple apps
What is MKV?
MKV is a flexible open container that can hold almost any video and audio codec, several audio languages, subtitles and chapters in one file. That makes it popular for movies, but iPhones, QuickTime, iMovie, many editors and most websites do not accept MKV — converting to MP4 makes it play everywhere.
- Holds any codec
- Multiple audio and subtitle tracks, chapters
- Open and royalty-free
- Not supported on Apple devices, many TVs and editors
- Rejected by most upload sites
Why GlideConvert?
- Private by design. Your files are converted on your own device by your browser — they are never uploaded to a server. That keeps them private, avoids upload waits and means there is no queue.
- Fast. Images convert in a fraction of a second; video uses your device’s hardware encoder and is often simply repackaged without re-encoding.
- Free. No sign-up, no watermark. 10 images, 5 audio files or one video at a time — Pro lifts the limits and removes ads.
Frequently asked questions
Will converting WebM to MKV lose quality?
Often not at all. If the WebM file already contains video and audio that MKV supports (H.264 video and AAC audio are the most common), they are copied as-is: no quality loss, and even a large file converts in seconds. Otherwise the video is re-encoded at high quality — choose a quality level or a target file size in the options.
How long does converting WebM to MKV take?
Usually much less than the length of the video: modern browsers encode video with your device’s hardware. Older formats such as WMV, FLV and AVI use a slower universal decoder.
Is there a file size limit?
On the free plan each video or audio file can be up to 500 MB and each image up to 100 MB. With Pro the limit is 4 GB per file. Because everything happens on your device, the practical limit for very large files is your device’s memory.
Are my files uploaded to a server?
No. GlideConvert runs entirely in your browser: images are processed with the browser’s built-in codecs and WebAssembly, video and audio with hardware-accelerated WebCodecs (or a WebAssembly build of FFmpeg for older formats). Nothing is sent anywhere — you can even disconnect from the internet once the page has loaded.
Does it work on iPhone, Android, Mac and Windows?
Yes. It works in any up-to-date browser — Chrome, Edge, Safari, Firefox or Samsung Internet — on phones, tablets and computers, with nothing to install. Long or 4K videos convert faster on a computer than on a phone.