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MKV to WEBM converter

Convert MKV to WEBM 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 WEBM
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 WEBM to MKV

Other ways to convert MKV

Convert other formats to WEBM

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

Should you convert MKV to WEBM?

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

WEBM also plays in far more places: Chrome, Firefox, Edge and recent Safari, but not the iPhone Photos app, many editors or social uploads.

MKV is a flexible container for any codec, with several audio and subtitle tracks; WEBM is the web’s open video format, holding VP8, VP9 or AV1 video with Opus or Vorbis audio. Use WEBM for video on your own website, especially short loops and clips with transparency.

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

How to convert MKV to WEBM

  1. 01

    Add your MKV

    Drop your MKV 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 WEBM. Change the quality if you want to; the defaults suit most files.

  3. 03

    Save the WEBM

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

What changes when MKV becomes WEBM

Often a straight copy

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

Extra tracks

MKV files can hold several audio and subtitle tracks. The main video and first audio track are converted; use Unpack a Video to save the others as separate files.

WebM needs the web’s codecs

WebM holds only VP8, VP9 or AV1 video with Opus or Vorbis audio, so most MKV files are re-encoded to VP9 and Opus. Recent Chrome and Edge do this on your graphics hardware; other browsers use a slower software encoder.

The size stays about the same

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

This page is put together from our notes on each format, choosing only what is true of MKV and WEBM, 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 MKV. Converting an MKV to a single-track format keeps only one audio track and drops soft subtitles unless you pick them.
  • About the WEBM. Browser screen recorders save WEBM, and the recording then fails to upload or attach almost everywhere else.
  • 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 MKV to WEBM lose quality?

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

Will a WEBM play on my phone?

WEBM opens in current browsers and apps: Chrome, Firefox, Edge and recent Safari, but not the iPhone Photos app, many editors or social uploads. Drag it into Chrome, Firefox or Edge, or open it in VLC.

Read more about this

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