How to use it
- Drop your WebM file onto the page.
- Keep Encode to H.264 on for the widest compatibility.
- Click Encode to MP4 and download the result.
Why WebM needs encoding
WebM files almost always contain VP8, VP9 or AV1 video with Opus or Vorbis audio. Those codecs are great for the web, but iPhones, QuickTime, many TVs and video editors won't play them, even inside an MP4. That's why the converter turns on Encode to H.264 by default for WebM: every frame is recompressed into H.264, the most widely supported video codec, and the audio is converted to AAC when your browser can encode it. Otherwise it stays Opus, which browsers, VLC and newer phones play.
Encoding takes longer than a simple repackage, from seconds to several minutes depending on the video's length, resolution and your device. If you only need an .mp4 file for a browser or VLC, you can untick encoding to copy the streams in seconds.
Everything happens in your browser; nothing is uploaded. Current Chrome and Edge, Safari 16.4+ and desktop Firefox 130+ are supported. For Matroska files, see MKV to MP4.
Frequently asked questions
Why won't my WebM play on iPhone or in Premiere?
It's usually the VP8 or VP9 video codec. Converting to MP4 with H.264 encoding fixes it.
How long does WebM to MP4 take?
It depends on the video's length and resolution and on your device, from seconds to several minutes. Keep the tab open while it runs.
Is my screen recording uploaded?
No. The file is converted in your browser and never leaves your device.
Last updated: November 12, 2026