Slimvid

Preset · MP4 to WebM · stays on device

Convert MP4 to WebM Online

Use WebM when a site or an HTML5 player asks for it. Use MP4 for iPhone, Discord and editors. If the MP4 is already VP8 or VP9, Slimvid can remux. H.264 is transcoded. Safari’s WebM support is better than it was and still not something to rely on alone, so keep the MP4.

Make a WebM from an MP4 when a site or HTML5 player asks for one.

Drop videos here, or click to browse

Up to 1GB each · MP4, MOV, WebM or MKV

Choose files

Processed locally in your browser. Nothing is uploaded.

Settings

Add a video and the settings for this tool appear here.

How it works

  1. 1Drop the .mp4 file.
  2. 2WebM is preselected on this page.
  3. 3Convert and download.

Processed locally in your browser. Nothing is uploaded.

Process videos up to 1GB on your device. Nothing is uploaded.

When WebM is the container you were asked for

Most browsers play MP4. WebM is the file you make because a publisher, a store listing or an embed asked for it.

A transcode from H.264 is not free in quality or time. A remux of existing VP8 or VP9 is.

Keep an MP4 copy for Apple devices.

What you get

Input
MP4
Output
WebM
Safari
Keep an MP4 as well

Up to 1GB in the browser.

Checked 2026-10-10.

Three steps

How to convert MP4 to WebM

Convert MP4 to WebM online for free, no upload. Local conversion for HTML5 pages and Chrome-friendly files.

  1. 1

    Drop your file

    Drop the .mp4 file.

  2. 2

    Choose settings

    WebM is preselected on this page.

  3. 3

    Download

    Convert and download.

All compress-video pagesVideo upload limits in 2026

Same job, other limits

Related size and platform pages

Convert WebM to MP4 OnlineTurn browser recordings into MP4 for iPhone, editors and chat apps.WebM to MP4Convert MOV to MP4 OnlineTurn iPhone and camera MOV files into an MP4 that plays in browsers, chat apps and slides.MOV to MP4Convert MKV to MP4 OnlineRemux an MKV into MP4 so phones, editors and chat apps will play it.MKV to MP4Compress Video for InstagramCut a heavy export down to 100MB before you post a Reel, feed clip or Story.For InstagramCompress Video for TikTokTurn a bulky edit into a 50MB file that uploads on cellular without looking mushy.For TikTok

Keep going

Related tools

FAQ

MP4 to WebM FAQ

Should I use WebM or MP4?
MP4 for phones, Discord and editors. WebM when the destination asked for WebM. This page is the second case.
Will it be smaller?
Often, if the picture is re-encoded. A remux of a VP8 or VP9 file stays about the same size.
Is anything uploaded?
No. The conversion runs in your browser.

Desktop · Coming soon

Desktop · Coming soon

The desktop app is in development. Join the waitlist for launch updates.

Get early accessCompare web vs desktop
  • No file size limit — 4K, hour-long recordings, anything
  • Batch queues: drop a folder, apply one preset
  • Hardware-accelerated encoding (H.264 / H.265)
  • Works fully offline, same privacy guarantee