Screen recordings and web downloads often come as WebM, which iPhones and many editors handle poorly. MP4 fixes that.
How to use the WEBM to MP4 converter
- Add your WEBM filesClick “Choose Files” or drag and drop them into the box. You can add many files at once — or paste a file with Ctrl+V.
- Choose MP4 and adjust settingsMP4 is selected automatically. Optionally open Settings to change resolution, quality or frame rate.
- Convert and downloadPress “Convert”. Your MP4 files appear instantly — download them one by one or all together as a ZIP.
WEBM vs MP4
WEBM WebM Video
WebM is an open, royalty-free format designed for the web. Browsers and screen recorders often produce it, but iPhones, QuickTime and many video editors handle it poorly.
- Compression
- Lossy (VP8/VP9/AV1)
- Features
- Video + Opus/Vorbis audio
- Origin
- 2010, Google
- Best for
- Web video, screen recordings
MP4 MPEG-4 Part 14
MP4 is the most compatible video format in the world. It plays on iPhones, Android, Windows, Mac, smart TVs and every browser, and is accepted by YouTube, Instagram, TikTok and WhatsApp.
- Compression
- Lossy (H.264/H.265)
- Features
- Video, audio, subtitles
- Origin
- 2001, MPEG
- Best for
- Sharing, social media, streaming
Why use ConvertMathly?
Files are processed on your device and never uploaded. Close the tab and they are gone.
No account, no daily cap, no queue and no watermark — convert as much as you want.
The same engine used by professional video tools, running in your browser via WebAssembly.
Windows, Mac, Linux, Chromebook, iPhone and Android — any modern browser, nothing to install.
Frequently asked questions
How do I convert WEBM to MP4?
Add your WEBM files above, make sure MP4 is selected and press Convert. The MP4 files are ready to download a few seconds later — no installation or account required.
Why does the first conversion take a little longer?
The video engine (FFmpeg compiled to WebAssembly, about 30 MB) is downloaded once and then cached by your browser. After that, conversions start immediately — even offline.
Is there a file size limit?
There is no artificial limit. Because the conversion runs in your browser, the practical limit is your device memory — files up to around 1–2 GB work on most computers. Long videos take longer on phones.
Are my WEBM files uploaded to a server?
No. ConvertMathly converts files entirely inside your web browser using JavaScript and WebAssembly. Your files never leave your computer or phone, which makes it safe for private photos and documents.
Can I convert multiple WEBM files at once?
Yes — add as many files as you like. They are converted one after another and you can download everything in a single ZIP.