# Convert WebM to MP4

> Convert WebM to MP4 online free: browser and screen recordings are re-encoded to H.264 MP4 that plays on every phone and TV. Many at once, no upload.

URL: https://nibbo.org/en/webm-to-mp4/

## WebM

WebM is the web’s open video format: screen recorders, browser extensions and sites that save clips with the MediaRecorder API produce it, with VP8, VP9 or AV1 video and Opus sound.

QuickTime, iMovie, many video editors and upload forms don’t accept WebM, while MP4 with H.264 plays everywhere.

## WebM to MP4: remux or re-encode

WebM can’t become MP4 without re-encoding: its picture codec isn’t one MP4 players read, so every frame is decoded and encoded again as H.264, with AAC sound.

WebM files are often large for what they show; at the Balanced preset a 1080p minute comes out around 30 MB. Files up to 3 GB are converted, and the FFmpeg path keeps the result in memory, so very long videos need a desktop browser.

## How it works

1. Drop one or more WebM files: MP4 is already selected. Quality, maximum resolution and sound can be changed before you start.
2. Streams that fit MP4 are copied; anything else is re-encoded with WebCodecs, or FFmpeg compiled to WebAssembly when the browser can’t.
3. Download each file, or all of them as one ZIP.

## Questions

### Are my videos uploaded?

No. Reading, remuxing and encoding all run in this browser tab. Open DevTools and watch the Network tab while a file converts: no request carries it.

### Why is one file done in seconds and another takes minutes?

A remux only copies the streams, so it runs at disk speed. A re-encode decodes and encodes every frame; FFmpeg in WebAssembly, used when the browser can’t, is slower still.

### How large can a video be?

Up to 3 GB per file for free, and as many files as you like. Remuxes and WebCodecs re-encodes stream from the disk; the FFmpeg path holds the result in memory.

## Related

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### Compress video

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