Video & Audio
WebM to MP4
Turn WebM videos into MP4 files with H.264 video and AAC sound. No upload, no signup.
Files stay on your device How it works
Drop files here, paste, or
WebM or MKV · up to 3 files, 25 MB each
Your files
Your file is ready
How to convert WebM to MP4
- Choose up to 3 WebM or MKV files, each up to 25 MB and 30 minutes long, or drop them on the box.
- Press Convert to MP4. A progress bar shows how far it has got, and Cancel stops it.
- Download each MP4, or all of them together as a ZIP: talk.webm becomes talk.mp4.
Why WebM needs converting
Screen recorders, browser extensions and websites often save video as WebM. Inside, the picture is VP8, VP9 or AV1, and the sound is Opus or Vorbis. Many phones, editing apps and upload forms expect MP4 with H.264 video and AAC sound instead, so a WebM may not open there, or may be refused.
What the conversion does
- The video is re-encoded as H.264, keeping its picture size up to 1920 × 1080. Larger video is scaled down to fit.
- The sound is converted to AAC. Firefox can’t make AAC, so there Opus sound stays Opus inside the MP4: browsers and VLC play it, though some older players may not.
- Already H.264: an MKV whose video is H.264 is copied as it is, which is quick and loses nothing.
How long it takes
Re-encoding means decoding and encoding every frame, so it can take a while for long videos, and longer on an older phone or laptop. Your browser’s own video encoder does the work, one file after another. Keep the tab open until it finishes; the progress bar shows how far it has got, and the note under each result says what’s inside.
Which browsers work
Current Chrome, Edge and Firefox, and Safari 16.4 or later, for the WebM videos it can read. On an iPhone or iPad, Safari’s version follows iOS. If your browser can’t re-encode video at all, the page says so as it opens, before you choose a file; if it can’t read one file’s video, the result says so for that file.
Good to know
Your files stay on your device: the conversion runs in your browser, and nothing is uploaded. To cut a recording down first, which also makes it quicker to convert, use Trim Video; it keeps the WebM as it is. To make the MP4 smaller afterwards, use Compress Video. For an iPhone’s MOV, use MOV to MP4, which usually copies instead of re-encoding.