Convert WebM to MP4
WebM is everywhere on the web — screen recorders, browser downloads, OBS clips — but it won't play on iPhones and plenty of upload forms reject it. Convert it to MP4 (H.264 + AAC) here, in your browser, and optionally shrink it to an exact size in the same pass.
Drop your video here
or
WebM files — processed 100% on your device
Target size
Planned output:
ð¦ Large file: encoding several hundred MB in your browser can take a very long time, and phones may run out of memory. Desktop Chrome recommended.
Loading encoder…
🔒 Your video never leaves your device. No upload, no signup, no watermark.
Convert WebM to MP4 in 3 steps
Drop your WebM file in
Drag and drop any WebM file into the tool above. It never leaves your browser — no upload, no queue, no account.
Convert to MP4
The tool re-encodes to MP4 at a generous 500 MB quality budget — or pick an exact smaller size if you also need the file under a limit.
Download your MP4
The MP4 downloads straight to your device, with faststart enabled so it plays and uploads cleanly.
Why convert WebM to MP4?
WebM is Google's open format and it is excellent inside Chrome — which is why screen recorders and web tools produce it. Outside Chrome, the story is worse: iPhones and Safari have historically balked at WebM, and many social platforms and editors expect MP4.
MP4 with H.264 video and AAC audio plays on every phone, every browser, and every platform. If your clip needs to travel beyond the browser, MP4 is the safe container.
VidSizer converts and, if you want, compresses in one pass: keep the 500 MB default budget for near-original quality, or set an exact target like 20 MB for Discord.
FAQ
Why won't my WebM file play on iPhone?
iPhones and Safari have limited or no WebM support depending on version. Converting to MP4 (H.264 + AAC) fixes it — the same file then plays on every phone.
Will converting WebM to MP4 lose quality?
Barely, at the default 500 MB budget: the video is re-encoded with a generous bitrate, so the result is visually near-identical to the original.
Is my video uploaded anywhere?
No. Everything runs in your browser. No upload, no account, no watermark.