Skip to content
Convert

Convert MKV to WebM

WebM is a restricted form of Matroska that browsers play natively. The video is re-encoded to a WebM codec so the file can be embedded on a web page or uploaded where WebM is required.

  • Nothing is uploaded
  • Free, no sign-up, no watermark
  • Works offline once loaded

Drop a video here

or choose a file

MKV, MP4, MOV, WEBM, AVI, M4V, 3GP, FLV, WMV and more

Processed on your device. Nothing is uploaded.

How to use Convert Video

  1. 1

    Add the video

    Drop a MOV, WebM, MKV, AVI or other video on the drop zone, or choose it from your device.

  2. 2

    Pick the output format

    Under Convert to choose MP4, WebM, MOV, MKV or AVI.

  3. 3

    Choose a method

    Fastest copies the streams when they already fit the new format, with no quality loss. Re-encode converts them for maximum compatibility and lets you set the Quality.

  4. 4

    Convert and download

    Press Convert, follow the progress, then Download the new file.

Why use Aback Video for this

  • Lossless remux

    When the video and audio codecs suit the new container, they are copied as they are. A MOV from an iPhone becomes an MP4 in seconds.

  • Compatible re-encode

    When the codecs do not fit, MP4 gets H.264 and AAC, WebM gets VP8 and Opus, AVI gets MPEG-4 and MP3.

  • Many inputs

    Opens MP4, MOV, WebM, MKV, AVI, M4V, 3GP, FLV, WMV, MPEG, TS, MTS and more.

  • Never uploaded

    The conversion runs in your browser. Your video stays on your device.

Frequently asked questions

MKV and WebM are related. Why re-encode?

WebM only allows open codecs such as VP8, VP9 and Opus. Most MKV files carry H.264 or HEVC, which are not allowed in WebM, so the video must be encoded again.

Will subtitles from the MKV be kept?

No. Extract them first with Extract Subtitles and convert them to VTT, which web players use alongside WebM.

Will converting reduce quality?

With Fastest, often not at all: if the streams can be copied, the new file contains exactly the same video and audio. If they must be re-encoded, the default high quality keeps the difference hard to notice.

Which format should I choose?

MP4 with H.264 plays on almost everything, so it is the safe choice. WebM suits websites. MOV suits Apple editing apps. MKV can hold many audio and subtitle tracks. AVI is for older software that requires it.

Why is my conversion slow?

It is being re-encoded, for example from HEVC to H.264 or into WebM. Re-encoding runs on one thread in the browser. Fastest finishes quickly whenever a copy is possible.

Is my video uploaded?

No. FFmpeg compiled to WebAssembly converts the file inside your browser tab.

Can it open every video?

Most common formats, yes. A few codecs are not included in this browser build, such as AV1 decoding and some professional camera formats. You will see a clear message if a file cannot be read.

Are subtitles and extra audio tracks kept?

The main video and audio tracks are converted. To keep subtitle tracks, extract them first with Extract Subtitles.

Does it work on phones?

Yes. Fastest is quick on phones; re-encoding long videos may take a while.

Related tools

Compress Video

Shrink a video's file size with simple quality presets.

Video to GIF

Make a sharp animated GIF from any part of a video.

Extract Audio

Save the sound of a video as MP3, M4A, WAV, OGG, FLAC or Opus.

Audio Converter

Convert between MP3, WAV, M4A, OGG, FLAC and Opus, from audio or video.

GIF to MP4

Turn an animated GIF into a much smaller MP4 or WebM video.

Video to Animated WebP

Make an animated WebP: GIF-like, but smaller and full colour.

Video to Frames

Save frames as JPG, PNG or WebP images, every N seconds or a set number.

Images to Video

Turn photos into a slideshow video, with music and fades.

Guides