MultiKit

Video Converter: MP4 and WebM in Your Browser, No Upload

  • Free
  • No sign-up
  • Runs in your browser
  • Version 1.0.2
  • Last updated 2026-11-09
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Convert a video to MP4, which plays on nearly everything, or to WebM for websites. Your own device does the work, so the video is never uploaded.

What this browser can make

    This depends on your browser, not on MultiKit. Chrome and Edge support the most.

    Everything you enter is processed in your browser and is never sent to a server.

    Browsers:Chrome94+Edge94+Firefox130+Safari16.4+Opera80+Samsung Internet17.0+BrowsersWhich formats it can read and write also depends on your browser and device; the tool shows what yours can do.

    How to use

    1. Drop the video onto the box, or choose it. MP4, MOV, WebM and MKV are accepted. You can play it to check.
    2. Choose the format. MP4 plays on phones, computers and TVs; WebM is for web pages. Formats your browser cannot make are turned off.
    3. Leave the size on Original, or pick a smaller one. Tick Remove the sound for a silent video. To keep only a part, type the start and the end.
    4. Press Convert. Keep the tab open until it ends, then press Download.

    Examples

    A phone video in MOV, to MP4
    → An MP4 of the same size
    MOV and MP4 hold the same kind of video; the conversion makes it play everywhere.
    A 4K video (3840×2160), to MP4 at 1080p
    → 1920×1080, and about a quarter of the video data per second
    At 30 frames a second the video data goes from about 27.4 to about 6.8 megabits a second, because it follows the number of pixels.
    A 1080p video at 30 frames a second, original size
    → About 6.8 megabits a second of picture and 128 kilobits of sound, so about 53 MB a minute
    A minute of 720p comes out at about 24 MB.
    A portrait phone video, 1080×1920, size set to 720p
    → 406×720
    The limit is on the height, the shape is kept and both sides are made even.
    A 10-minute video, only 2:00 to 3:30
    → A 90-second video
    Only the part between the times is kept. Times can be typed as 150, 2:30 or 1h2m3s.

    How it works

    The video is read by the open-source Mediabunny toolkit (MPL-2.0) and decoded and encoded by the WebCodecs of your browser, hardware-accelerated when the device allows. Before a conversion the page checks what this browser can do and turns off what it cannot, and it says so when the file’s own sound or picture cannot be read here, instead of making a broken file.

    How the size of the file is set

    The picture is written at a fixed number of bits for each pixel of each frame, so the bitrate follows the picture and the file follows the length.

    Video Picture data About a minute, with sound
    1280×720, 30 frames a second 3.0 megabits a second 24 MB
    1920×1080, 30 frames a second 6.8 megabits a second 53 MB
    3840×2160, 30 frames a second 27.4 megabits a second 210 MB

    A video that is trimmed is estimated on the part that is kept, and a video without sound, or with the sound removed, saves the 128 kilobits a second of the sound track.

    Which codecs are tried

    For MP4 the page tries H.264, then H.265, VP9 and AV1 for the picture, and AAC, Opus and MP3 for the sound. For WebM it tries VP9, VP8 and AV1, and Opus and Vorbis. It uses the first one your browser can write at the size you chose, so the same file can come out with a different codec in a different browser. An MP4 is written with its index at the start, so it can begin to play before it has all been downloaded.

    What it does not do

    It does not change the frame rate, and it does not choose a size for you: Original keeps the pixels as they are. To aim for a file size, such as an upload limit, use the video compressor.

    The bitrate rule, the size limits, the time input and the file estimates are tested.

    Sources

    Frequently asked questions

    MP4 or WebM?
    MP4 plays almost everywhere. The page writes it with H.264 and AAC when your browser can, and with another codec that MP4 allows when it cannot. WebM (VP9 or VP8 with Opus or Vorbis) is open and suits web pages, but some TVs and older devices cannot play it.
    Does it lose quality?
    Video is always written again, so a little is lost. This tool aims for about 0.11 bits per pixel per frame, which is a high setting. To make the file smaller, use the video compressor.
    How is the quality chosen?
    From the size of the picture and its frame rate: width times height times frames a second times 0.11. A frame rate above 60 counts as 60, an unknown one counts as 30, and the result never drops below 150 kilobits a second. The sound is written at 128 kilobits a second.
    What do the size choices do?
    They set the longest allowed height: 1080, 720, 480 or 360 pixels. The shape of the picture is kept, both sides are made even because video codecs need that, and a video that is already smaller is never enlarged.
    What does Remove the sound do?
    The sound track is left out of the new file. The file is a little smaller, and the picture is unchanged.
    Why is it slow?
    Your device does all the work, and video is a lot of data. A short clip takes seconds, a long film can take longer than its own length on a weak device. Keep the tab open.
    Why can I not choose some format?
    This page uses the audio and video codecs built into your browser, so what it can read and write depends on the browser. The list under the tool shows what yours can make. Chrome and Edge support the most.
    How big a video can it take?
    Up to 2 GB, and the result is made in the memory of the tab. For a longer video, keep a part, or use a computer with more memory.
    Is my video uploaded?
    No. It is converted in your browser.
    Version history
    • 1.0.2 — Adds how the picture quality and file size are set (with sizes per minute), which codecs are tried for MP4 and WebM, what the size choices and Remove the sound do, and examples for them.
    • 1.0.1 — Makes the search title and description state the supported task, key formats and privacy benefit more clearly.
    • 1.0.0 — First release.

    Last updated: