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Convert video to WebM

Turn MP4, MOV and MKV files into WebM with VP9 video and Opus sound. Converted on this device, not uploaded.

Converts MP4, MOV and MKV videos to WebM with VP9 (or VP8) video and Opus sound, copying WebM streams as they are, and says so when a browser cannot write WebM. It is free, needs no account and adds no watermark, and your files are not uploaded: everything runs in your browser on your device. The size limit is your device’s memory, and phones hold less; give the page a short while after one visit to save itself for offline use, and then it works offline.

Drop videos to convert to WebMor click to choose files. Batches welcome.

    VP9 or VP8 video and Opus sound are copied as they are. Anything else is re-encoded to VP9 (or VP8) and Opus, which takes longer than a copy.

    Working…

    Done

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    Your files are processed on this device and never sent to a server. Reload the page to clear everything from memory.

    How it works

    1. Drop one or more videos (MP4, MOV, WebM or MKV), or tap to pick them.
    2. Tick Remove the sound if you want a silent video. There is nothing else to set.
    3. Convert. Your browser re-encodes the picture to VP9 (or VP8) and the sound to Opus. One downloads straight away, several download as a zip.

    In your browser, not on a server

    Mediabunny (MPL-2.0), a media toolkit written in TypeScript, reads the MP4, MOV, MKV or WebM container in your tab and writes a WebM. VP8, VP9 or AV1 video and Opus or Vorbis sound already in the file are copied across as they are. Anything else is decoded and re-encoded by your browser’s own encoders (WebCodecs), VP9 where the browser can write it and VP8 otherwise, with the sound as Opus. A browser with no VP8 or VP9 encoder says so instead of writing a broken file.

    Compared with upload-based tools: The video is read from your disk and the WebM is written in memory on your device, so there is no upload to wait for and the only limit is how much memory your device has.

    Verify it yourself. Give the page a short while after one visit to save itself for offline use, then turn off Wi-Fi or switch to airplane mode and run the tool again. Or open your browser's developer tools (F12, or Cmd-Option-I on a Mac), pick the Network tab, and watch it while you convert. The panel above does the same count for you.

    Questions

    Is my video uploaded?

    No. The file is read and written by code in this page, and the encoding is done by your browser’s own video encoder. There is no server in the process. After one visit and a short wait the page works offline.

    Should I expect VP9 or VP8?

    VP9 where your browser can write it, because it makes smaller files at the same quality. VP8 is the fallback for browsers that can only write that one. The line under the result says which one you got. Both play in Chrome, Edge and Firefox, and in current Safari.

    Why can some browsers not write WebM?

    WebM needs the browser to have a VP8 or VP9 video encoder and an Opus sound encoder, and each browser ships a different set. Safari only added them recently: Safari’s engine (WebKit 26.6 on a Mac) writes VP9 video and Opus sound here, but older versions, and some Linux builds of Chrome, may not. When yours is missing one, the page says so and writes no file, rather than producing something broken. Chrome or Edge on a computer write WebM.

    Why did it take longer than converting to MP4?

    An MP4 holding H.264 can often be copied into a MOV or another MP4 as it is, but H.264 cannot go into a WebM, so every frame is decoded and encoded again. Files that are already WebM (VP8, VP9 or AV1 with Opus) are copied as they are.

    More video and audio tools

    Trim video

    Cut a clip out of a longer video without uploading it. Most cuts take seconds and keep the original quality.

    Video splitter

    Cut one video into parts at the times you choose, every so often or into equal pieces, and save them in one zip. Done on this device, and the video is not uploaded.

    Mute video

    Take the sound out of a video, in seconds and without re-encoding. The video never leaves this device.

    Resize video

    Change a video’s resolution, from 4K down to 240p or to a width and height you choose. Resized on this device, never uploaded.

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