Convert MOV to MP4
Turn QuickTime MOV files into MP4. When the video is already H.264 it is copied across in seconds with zero quality loss — and never uploaded.
- Runs in your browser
- Files are never uploaded
- Free, no account
First use downloads the 10 MB video engine from this site. After that it is cached and works offline. It is WebAssembly served from onthisdevice.com — no third-party CDN — and your file is still processed entirely on your own device.
How to convert MOV to MP4
- Drop your .mov file onto the box above, or click it to browse.
- Optionally press Check what is inside first — FFmpeg reads the header and tells you which codecs the file holds and whether they can simply be copied.
- Press Convert to MP4. The first run downloads the 10 MB video engine from this site once; after that it is cached and works offline.
- Watch the real percentage, preview the result in the page, and download it.
Why this can finish in seconds
A video file is two separate things: the container — MOV, MP4, MKV — which is metadata describing where each chunk of data sits, and the codec — H.264, HEVC, ProRes — which is how the pictures themselves are compressed. MOV and MP4 are unusually close relatives: both are built on the ISO base media file format that Apple originally created as QuickTime and then donated to the standards body that turned it into MP4.
So when your MOV already contains H.264 or HEVC video and AAC audio — which covers almost every iPhone recording, every DSLR clip and every QuickTime export — the picture data does not need to be touched at all. FFmpeg copies each compressed packet into a new container and writes a new index. That is called a remux, and it is why a 2 GB file can convert faster than an upload service could even receive it.
| What is inside your MOV | What happens | Speed | Quality |
|---|---|---|---|
| H.264 + AAC (iPhone, most cameras) | Streams copied into MP4 | Seconds | Identical — nothing re-compressed |
| HEVC / H.265 + AAC (iPhone “High Efficiency”) | Streams copied into MP4 | Seconds | Identical, but needs a recent player |
| H.264 + PCM audio (screen capture, some editors) | Video copied, audio re-encoded to AAC | Fast | Picture untouched, audio effectively unchanged |
| Apple ProRes / Animation (editing masters) | Full transcode to H.264 | Around real time | Much smaller file, some loss |
Windows will not play my iPhone MOV
Two different problems hide behind that complaint. If the file will not open at all, it is the container: Windows Media Player has never handled QuickTime well, and converting to MP4 fixes it outright. If the file opens but shows a black screen or an error about a missing codec, the problem is HEVC, which Windows charges for a decoder to play. In that case copying the streams is not enough — set the method to always re-encode so the video is rewritten as H.264, which every version of Windows plays without extra software.
You can avoid the issue at source: on an iPhone, Settings → Camera → Formats → Most Compatible records H.264 instead of HEVC.
What this tool does not do
- It does not encode ProRes. It can read ProRes MOV files and convert them down to H.264, but it cannot produce a ProRes master — that needs a desktop encoder.
- It does not edit. Trimming, cropping and rotating are separate tools on this site so that each one stays a single, obvious job.
- It does not strip a MOV that is genuinely damaged. If the recording was cut short and the index (the “moov atom”) never got written, no converter can recover it, and this one says so instead of producing a zero-byte file.
Why do it in the browser at all
The usual online converter uploads your footage, converts it on a rented machine and gives you a link — which is why those sites cap files at 100 MB or 1 GB, queue you behind other people and delete results after an hour. Your video sits on someone else’s disk in the meantime. Here the same FFmpeg code runs as WebAssembly inside your tab, so the size limit is your own memory, there is no queue, and the file physically cannot leave the device: the site’s content security policy lists no third-party origin it could be sent to.
Questions
Why is a MOV to MP4 conversion sometimes instant?
Because most MOV files from an iPhone, a DSLR or QuickTime already contain H.264 or HEVC video and AAC audio — exactly what an MP4 holds. Only the container has to change, so the compressed data is copied packet by packet instead of being decoded and re-compressed. A 2 GB clip can finish in a few seconds and comes out visually identical.
When does it have to re-encode instead?
When the MOV holds something MP4 cannot carry — Apple ProRes, Animation, or uncompressed PCM audio, all common in footage straight out of an editing suite. The page tells you which of the two paths it took before it starts, and again on the result.
Is there a file size limit?
There is no limit imposed by us, because there is no server to impose one. The practical ceiling is your device: browsers give WebAssembly roughly 2 GB of working memory, and a stream copy needs far less of it than a re-encode.
Does the audio stay in sync?
Yes. On the copy path the timestamps are carried over untouched. On the re-encode path FFmpeg keeps the original presentation timestamps, so variable-frame-rate iPhone footage does not drift the way it does in some cheap converters.
Will the MP4 play on Windows and Android?
H.264 MP4 plays on essentially everything made since about 2008. HEVC MOV files copied into MP4 keep HEVC, which needs a recent device — if a player refuses it, run the file again with the method set to “always re-encode”.