Convert WebM to MP4

WebM is what browsers produce when they record: Loom-style screen recorders, online webcam recorders, Google Meet recordings saved by extensions, and many clips downloaded from the web. It uses VP8 or VP9 video with Opus sound, which Chrome and Firefox play well but iPhones, PowerPoint, Premiere and many upload forms do not.

This page re-encodes the picture to H.264 and the sound to AAC, the combination that plays everywhere, using the video encoder built into your browser. Browser recordings often leave out the video’s length, which confuses some converters; the whole file is read here, so the MP4 gets the right duration and seeks properly.

The recording never leaves your device. Screen recordings are full of private things, from open tabs to notifications, and here there is nothing uploaded to show them to.

Expect the MP4 to be a different size from the WebM, often larger. VP9 fits more picture into each megabit than H.264, and the page re-encodes at a high quality setting so that text in a screen recording stays sharp. If the MP4 comes out bigger than you want for email or chat, run it through Compress video afterwards. Compress video also reads WebM and writes MP4 directly, so when size is the goal you can go straight there and choose a size limit in one step.

Animated stickers, overlays and some exports from design tools are WebM files with a transparent background. H.264 MP4 has no transparency, so those see-through areas are filled in and the clip plays as a solid rectangle, usually on black. Keep the WebM if the transparency matters, for example on a web page. For an ordinary recording none of this applies, and the MP4 embeds in PowerPoint and Keynote and plays like any camera video.