Convert WebM to MP4

Why convert WebM to MP4?

MP4 is the most widely supported video format. Converting from WebM fixes "unsupported file" errors on phones, social sites, presentation apps and video editors.

How the conversion works

The WebM video is decoded and re-encoded to H.264 with AAC audio. That combination plays on nearly every phone, browser, TV and editor.

What's inside a WebM file?

WebM is an open video container made for the web. Its video track is VP8, VP9 or AV1, and its audio is Vorbis or Opus. Chrome and other browsers save screen and webcam recordings as WebM. Many sites serve WebM clips too, so it is easy to end up with one. The problem starts outside the browser. QuickTime Player, many video editors, presentation apps, older phones and smart TVs expect H.264 video in an MP4. To them, a healthy WebM can look like a broken file.

Why WebM to MP4 means a re-encode

The WebM spec only allows VP8, VP9 and AV1 video, and MP4 players expect H.264. There is no lossless shortcut like the remux used for MOV and MKV files. The video is decoded and re-encoded to H.264, also called AVC. Opus or Vorbis audio is re-encoded to AAC at 160 kbps. If your browser has suitable WebCodecs decoders and encoders, the tool uses them. If not, it falls back to FFmpeg compiled to WebAssembly and encodes with x264 at CRF 23 using the veryfast preset.

How to convert WebM to MP4

Drop one or more .webm files above and press Convert all. Each file is decoded and re-encoded in your browser, and a progress bar shows how far it has got. Download the MP4s one by one, or as a ZIP when several are done. Keep the tab open until the last file finishes.

Converting long screen recordings

Every frame is re-encoded, so conversion time grows with the length and resolution of the clip. If you only need part of a long recording, trim it first. Trim Video accepts WebM and cuts without re-encoding, which leaves less work for the conversion.

• Open Trim Video and drop the WebM file.
• Enter a start and end time and download the trimmed WebM.
• Drop the trimmed file here and press Convert all.

Encoding happens on your device

Video encoding runs in this browser tab, on your own device. There is no upload and no queue. Your device does all the work, so a large or long clip can take a minute or more.

Before you start

Input: WEBM. Output: MP4. The settings appear before anything runs, so you can check them first. Your original file is never changed.

Video work uses a lot of memory and CPU. Try a short clip first and check that the sound and playback work. On a phone, split large batches into smaller ones.

Keep the original until you have opened and checked the result. The work happens in this browser tab, so the size you can handle depends on your device's memory, your browser and the file itself.

Steps to convert WebM to MP4

1. Drop one or more .webm files into the converter above, or browse to select them.
2. Press Convert all. The video is re-encoded to H.264 and the audio to AAC.
3. Keep the tab open while the progress bar runs. Longer clips take longer.
4. Download each MP4, or download them all as a ZIP when several files are done.