Local-first media tools
Free WebM to MP4 converter.
Your files stay on your device.
Convert a WebM recording to an MP4 locally in your browser. Nothing personal is uploaded, stored, or sold.
The studio
WebM to MP4. No catch.
Choose your WebM file and download the completed MP4 directly from your browser.
More formats
WebM to MP4 converter
Convert a WebM recording to an MP4 locally in your browser. The engine runs on your device, never on our servers.
First use downloads the public local conversion engine (about 31 MB). Your media file is never uploaded.
Copyright & lawful use: convert only media you own, are licensed or permitted to use, or may lawfully use. Lumen does not bypass DRM or determine rights status.
Free browser-based media conversion
About the WebM to MP4 converter
Convert a WebM recording to an MP4 locally in your browser. Lumen Convert is free for creators who want a simple, private way to change media formats.
Your file is processed locally on your own device. There is no account to create, no credit card to add, and no forced watermark on your export. Please only convert media you own or are permitted to use.
Help centre
Frequently asked questions
How do I convert WebM to MP4?
- Choose your WebM file above, then select Convert to MP4. The conversion runs locally in your browser and the completed file is ready to download directly to your device.
Is Lumen Convert free to use?
- Yes. Lumen Convert is free to use with no account, subscription, credit card, payment screen, or website-imposed daily conversion quota.
Do my files leave my device?
- No. Your media is processed locally in your browser. Lumen Convert does not upload, store, or sell the files you choose.
Which formats can I convert?
- You can convert WAV and MP3 audio, plus MOV to MP4, M4A to MP3, MP4 to MP3, MKV to MP4, and WebM to MP4.
Is there a file-size limit?
- Lumen Convert does not impose an artificial file-size limit. The practical limit depends on your browser, available memory, battery, and free disk space.
Can I create a music visual with my own artwork?
- Yes. Add your own image as a local backdrop, adjust its crop and contrast, customise the title and waveform, and export the visual on your device.
A different kind of creative tool
Free means free. Forever.
Lumen runs on your own browser and your own device. Your files stay with you, and the studio never puts a payment screen between you and your export.
Your device, browser, available memory, and free disk space determine the practical size it can handle — not a website quota.