WebM to MP4 Converter
Convert WebM (VP8/VP9) videos to H.264 MP4 for editors and older devices, in your browser. Free, private, no upload.
About the WebM to MP4 Converter
This free WebM to MP4 converter turns web-native WebM (VP8/VP9) videos into H.264 MP4 — the format that video editors, older devices and many social apps expect. WebM is great for the web but is not accepted everywhere; converting to MP4 makes your clip universally usable.
The conversion runs in your browser through FFmpeg WebAssembly, so your video is never uploaded. The engine (about 30 MB) downloads from a CDN on first use and is cached, so the first conversion is the slow one. The output uses a web-friendly yuv420p pixel format and even dimensions for full compatibility.
Converting re-encodes the video, so it takes a little time and cannot add quality beyond the WebM source. Because MP4/H.264 is less efficient than VP9, the MP4 can sometimes be a little larger — that is normal. Files up to 100 MB are supported.
How to Use the WebM to MP4 Converter
- 1Choose a WebM file, up to 100 MB.
- 2Pick a quality — Balanced is recommended.
- 3Click Convert to MP4 and wait for the progress bar.
- 4Preview the MP4 and download it.
Frequently Asked Questions
Is my file uploaded to a server?
No. All processing runs in your browser using FFmpeg compiled to WebAssembly. Your file never leaves your device — only the converter engine is downloaded, once.
Why is the first run slow?
The first time you use any converter here, the browser downloads the FFmpeg core (about 30 MB) from a CDN and compiles it. It is then cached for the session, so later runs are much faster.
Why convert WebM to MP4?
WebM is a web format that some editors, older devices and social apps do not accept. MP4 with H.264 works almost everywhere, so it is the safe choice for sharing and editing.
Why is the MP4 sometimes larger than the WebM?
WebM's VP9 codec is more efficient than H.264, so the same quality can take a bit more space as MP4. Choose a lower quality setting if you need a smaller file.
Is there a file size limit?
Yes, 100 MB per file. Because everything runs in your browser's memory, very large files can be slow or run out of memory. Trim long clips first if you hit the limit.