Convert video to MP4
Convert MOV, WEBM, AVI, MKV and more to MP4 (H.264/AAC) directly in your browser. Your file is never uploaded — conversion runs entirely on your device.
Your file is processed entirely in this browser tab. It is never uploaded, stored or seen by anyone.
To convert a video to MP4, drop the file into the converter above and select MP4 as the output. The file is transcoded to H.264 video with AAC audio inside your browser using WebAssembly, so it is never uploaded to a server. Files up to 200MB work on desktop.
How it works
- Choose your file
Drag a file onto the converter, or click to browse. Nothing is uploaded — the file is read directly by your browser.
- Convert to MP4
Press Convert. FFmpeg runs as WebAssembly inside the tab and shows real progress as it works.
- Download the result
When it finishes, download the MP4 file. It is created in your browser's memory and never sent anywhere.
Your file never leaves your device — conversion runs entirely in this browser tab.
About MP4
MP4 is a container, not a codec — a distinction that causes more confusion than any other in video. The container is the wrapper that holds the streams and tells a player how they fit together; the codec is the algorithm that compressed the picture. An MP4 file almost always contains H.264 video and AAC audio, but it can legally hold H.265, AV1 or even MPEG-4 Part 2.
That matters when a file "will not play" despite ending in .mp4. The container is fine; the codec inside it is not supported. Converting to MP4 with H.264 specifically — which is what this tool does — is the reliable fix, because H.264 has hardware decoding on effectively every device manufactured in the last fifteen years.
This converter encodes with a Constant Rate Factor of 23, the widely used default that targets visually transparent quality at a sensible file size, and moves the moov atom to the front of the file with faststart so the video begins playing before it has fully downloaded.
| Codec | H.264 (AVC) + AAC |
|---|---|
| Container | MPEG-4 Part 14 |
| Typical bitrate | 2–20 Mbps at 1080p |
| Compatibility | Universal — every browser, phone, TV and editor |
| Best for | Uploading to YouTube, sharing, near-universal playback |
Limits you should know about
Because conversion happens on your device rather than on a server, the ceiling is your browser's memory rather than our disk space. Files under 50MB work reliably everywhere. Desktop browsers stretch to roughly 200MB; mobile browsers, and iOS Safari in particular, cut out closer to 40MB.
Speed is the other trade. Running FFmpeg through WebAssembly is 5–10× slower than a desktop app, so a conversion that takes thirty seconds in a desktop application can take several minutes here. The converter shows a real estimate before it starts, and the tab has to stay open while it runs.
If your file is beyond those limits, trim it first, or use a desktop application such as HandBrake or FFmpeg directly — neither has a size ceiling.
Common questions
Is converting to MP4 lossy?
Yes. Re-encoding to H.264 discards data, so a converted file is never identical to the source. The loss is usually invisible at CRF 23, but converting the same file repeatedly compounds it. Always convert from your original, not from a previous conversion.
Should I upload MOV or MP4 to YouTube?
Either works, and YouTube re-encodes both on arrival. MP4 with H.264 uploads faster because the files are smaller, and it is what YouTube itself recommends. MOV from an Apple device is fine but often much larger for the same picture quality.
Does this work on iPhone?
It works for small files, but iOS Safari is aggressively memory-limited and will terminate the tab on large ones. Keep mobile conversions under about 40MB. Anything larger should be converted on a desktop.
Why is conversion slower than a desktop app?
The converter runs FFmpeg compiled to WebAssembly inside your browser tab rather than as native code, which costs roughly 5–10× in speed. That is the trade for never uploading your file to anyone else’s server.
What is the maximum file size?
Around 200MB on a desktop browser and roughly 40MB on mobile. Below 50MB it works reliably everywhere. Larger files exhaust the memory the browser will grant a single tab.