MP4 to WebM
WebM is an open video format that websites, web apps and some game engines prefer. Turn MP4 videos into WebM with VP9 video and Opus sound. Everything happens on your own device, using the video engine built into your browser, so your video is never uploaded.
How to use it
- Choose your MP4 videos, or drag them onto the box.
- Each one is converted on your device; this takes a little while for long videos.
- Download each WebM, or all of them together as a ZIP file.
Which browsers can do this?
Making WebM video needs the VP9 encoder built into the browser. Current versions of Chrome, Edge and Firefox have one; the page tells you straight away if yours does not.
What is kept
The main video and its sound are kept. Subtitles and any extra sound tracks, such as a second language, are left out, and the result says when this has happened.
Limits
Videos are converted in the browser's memory, so very large files are refused before anything starts; the page shows the largest size tested on your kind of device. Long videos take a while, and the page must stay open and on screen while it works, particularly on a phone.
The page reads what is inside each file before it starts. Dolby Digital (AC-3) sound, which many camcorders use, is read by FilePresto's own converter, on your device. A few formats cannot be converted yet: WMV videos, and Dolby Digital Plus (E-AC-3) and DTS sound. If a file has sound that cannot be read, the page stops and says so, rather than making a silent video; you can then choose to convert the video without its sound.
Questions
Are my files uploaded?
No. The work happens inside your web browser, on your own device. Before your file is opened, this page locks itself: from then on your browser refuses to let it fetch, upload or send anything at all. You can check: once the page has loaded, switch off your internet connection and it will still work. How the lock works.