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WEBM to MKV converter

Convert WEBM to MKV in your browser. No upload and no account: the file never leaves your device, so the only size limit is your device’s memory.

I want MKV
Quality

Applies only when the video has to be re-encoded. A straight copy keeps the original quality.

Advanced 2
Always re-encode Rebuilds the picture as H.264 (VP9 for WebM) even when it could be copied. Fixes files that won’t play on older TVs and PCs.

Bytes of your files sent anywhere: 0 B

Related conversions

Need it the other way round? Convert MKV to WEBM

Other ways to convert WEBM

Convert other formats to MKV

Read more about the WEBM format and the MKV format, or see every video tool and all video conversions.

Should you convert WEBM to MKV?

Usually a quick, safe conversion. MKV can carry VP8, VP9 or AV1, which is what WEBM files normally contain, so the video can often be copied across without re-encoding: fast, and with no loss at all.

Check that MKV is really needed: it plays in VLC, Plex, Kodi and many smart TVs, but not iPhones, most editors or social apps, while WEBM is opens in current browsers and apps.

WEBM is the web’s open video format, holding VP8, VP9 or AV1 video with Opus or Vorbis audio; MKV is a flexible container for any codec, with several audio and subtitle tracks. Use MKV for a media library where one file should carry every language and subtitle.

WEBM and MKV compared
Property WEBM MKV
Usually contains VP9 or AV1 video with Opus audio H.264 or HEVC video with AAC, AC-3 or Opus audio, often plus subtitles
Support Opens in current browsers and apps Has patchy support
Plays on Chrome, Firefox, Edge and recent Safari, but not the iPhone Photos app, many editors or social uploads VLC, Plex, Kodi and many smart TVs, but not iPhones, most editors or social apps
Best for Video embedded in web pages, and browser screen recordings Films and series with several languages and subtitle tracks
Introduced 2010 2002

How to convert WEBM to MKV

  1. 01

    Add your WEBM

    Drop your WEBM video onto the box, or click to choose it. It is read from your disk and stays there.

  2. 02

    Check the settings

    The output is already set to MKV. Change the quality if you want to; the defaults suit most files.

  3. 03

    Save the MKV

    Press convert and save the MKV. Several files come back together as a ZIP.

What changes when WEBM becomes MKV

Often a straight copy

When the WEBM holds VP8, VP9 or AV1 video, the stream is moved into the MKV container untouched, so the conversion takes seconds even for long files. If the codec inside is something MKV can’t hold, the picture is re-encoded instead and you’ll see a progress bar that takes longer.

The size stays about the same

WEBM and MKV are close in size for the same content, so do this for compatibility rather than to save space. WEBM: Usually a little smaller than MP4 at the same quality. MKV: Depends entirely on the codec inside.

This page is put together from our notes on each format, choosing only what is true of WEBM and MKV, so every pairing states the same facts the same way. How these pages are made.

Why it doesn’t upload

Video files are big, and uploading one just to change its container can take longer than the conversion itself. Your browser can read and write these formats, so the file never has to leave your device.

How to check for yourself

Worth knowing

  • About the WEBM. Browser screen recorders save WEBM, and the recording then fails to upload or attach almost everywhere else.
  • About the MKV. Converting an MKV to a single-track format keeps only one audio track and drops soft subtitles unless you pick them.
  • MP4, MOV, MKV and WebM are handled by your browser’s own video engine, often with hardware help. AVI, WMV, FLV, MPG and the other older formats use the FFmpeg engine, a one-time 31 MB download, and are slower.

Questions

Does converting WEBM to MKV lose quality?

Not when the video can be copied, which is the case for most WEBM files: the stream moves into MKV untouched. If it has to be re-encoded, the default quality keeps the difference invisible.

Will a MKV play on my phone?

MKV has patchy support: VLC, Plex, Kodi and many smart TVs, but not iPhones, most editors or social apps. VLC, mpv, IINA and Plex play MKV files; QuickTime and most phone galleries don’t.

Read more about this

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