User Guide
Add the .mov file
Drag it in or click to browse. iPhone and QuickTime recordings are the usual sources. The engine downloads once (~30 MB) and is then cached.
Note the size before you start
iPhone 4K at 60 fps runs to roughly 400 MB per minute, which exceeds the 300 MB ceiling almost immediately. Check the file size first — if it is over, trim or compress before converting.
Press Convert
Video is encoded to H.264 and forced to yuv420p chroma; audio becomes AAC. The yuv420p step is what makes the result open in Windows, Android and PowerPoint rather than showing a green screen or refusing to load.
Let it finish writing the index
The tool applies +faststart, which relocates the file index to the front. This is what lets the video begin playing before it has fully downloaded — essential if you are uploading it to a website.
Download and test on the target device
The whole point is playing somewhere QuickTime does not reach. Test it there: the Windows machine, the Android phone, the presentation laptop.
If the file is rejected as too large
Cut it down with the Video Trimmer, or reduce the resolution with the Video Compressor, then convert the smaller result.
About the MOV to MP4 Converter
MOV and MP4 are close relatives. Apple published the QuickTime File Format in the early 1990s, and ISO adopted its structure as the base media file format from which MP4 was built. Both are built from the same nested atom structure. In many cases the only meaningful difference between a .mov and a .mp4 is the four bytes of the brand identifier and what the file is allowed to contain — the Apple QuickTime File Format documents the atom layout they share.
Which raises the obvious question: if they are so similar, why does the .mov refuse to open?
Three reasons a MOV fails elsewhere
The codec is Apple-specific. QuickTime is permitted to hold ProRes, Apple Intermediate, Animation and Motion JPEG A/B. None of these exist outside the Apple ecosystem. A ProRes .mov opens instantly in Final Cut and not at all on Windows.
The chroma format is too rich. Professional and screen-recorded MOV files are often 4:2:2 or 4:4:4, sometimes 10-bit. Consumer H.264 decoders — including the hardware decoder in most phones and the one Chrome uses — only handle 8-bit 4:2:0. A file that is technically valid H.264 will still show a green screen, play as garbage, or refuse to load. This is why the tool forces -pix_fmt yuv420p on every conversion.
The index sits at the end. QuickTime often writes the moov atom after the media data. A player then has to download the entire file before it can start. On a website that reads as a broken video. The +faststart flag this tool applies moves that index to the front.
What the conversion does
| Step | Setting | Why it matters |
|---|---|---|
| Video codec | H.264, veryfast preset |
Hardware-decoded on essentially every device |
| Chroma | yuv420p |
Fixes green screens and refusals on Windows and Android |
| Audio codec | AAC-LC | The MP4 default every player expects (FFmpeg AAC guide) |
| Index position | +faststart |
Lets playback start before the file finishes downloading |
Working with iPhone video
Most MOV files that reach this page came from an iPhone, and size is the constraint that bites. Approximate recording rates:
| iPhone setting | Roughly per minute | Fits in 300 MB? |
|---|---|---|
| 720p HD, 30 fps | ~40 MB | About 7 minutes |
| 1080p HD, 30 fps | ~65 MB | About 4 minutes |
| 1080p HD, 60 fps | ~100 MB | About 3 minutes |
| 4K, 30 fps | ~190 MB | Around 90 seconds |
| 4K, 60 fps | ~400 MB | No — compress first |
Note also that recent iPhones default to HEVC (H.265) inside the .mov rather than H.264. That plays on Apple hardware and inconsistently everywhere else — another reason the re-encode to H.264 is worth the one generation of loss.
Privacy
Everything runs through a WebAssembly build of FFmpeg that is downloaded into the browser tab on first use (about 30 MB, cached afterwards). The video itself is never transmitted — there is no upload step, no server-side queue and nothing to delete afterwards. Because a single-threaded WebAssembly module is capped at roughly 2 GB of addressable memory, files above 300 MB are rejected outright and anything over 60 MB shows a slow-work warning before it starts. For personal video — which is what most MOV files are — that distinction matters more than the speed penalty.
Frequently Asked Questions
Is MOV basically the same thing as MP4?
Structurally, nearly. MP4 was derived from Apple’s QuickTime format and both use the same nested atom layout. The differences that matter are what each is allowed to contain: MOV can hold ProRes, 4:2:2 chroma and Apple-only codecs that MP4 players will not decode.
Why does my MOV show a green screen on Windows?
Almost always chroma subsampling. Screen recordings and professional footage are often 4:2:2 or 10-bit, and consumer H.264 decoders only handle 8-bit 4:2:0. The tool forces yuv420p on every conversion, which is exactly the fix for this.
What does faststart do?
It moves the file’s index (the moov atom) from the end to the beginning. Without it a player must download the whole file before showing anything, which looks like a broken video on a website. With it, playback starts immediately.
My 4K iPhone video is rejected as too large. Why?
4K at 30 fps records at roughly 190 MB per minute and at 60 fps around 400 MB, so it passes the 300 MB ceiling within a minute or two. Trim the section you need first, or run it through the Video Compressor.
Will the quality drop?
By one encoding generation. The tool re-encodes rather than rewrapping, because the codec or chroma format inside a MOV is usually the reason it would not play. The default CRF 23 is chosen to be visually transparent.
Does this handle iPhone HEVC video?
Yes. Recent iPhones record H.265/HEVC inside a .mov, which plays on Apple devices and unreliably elsewhere. Converting to H.264 is precisely what makes those files portable.
Is my video sent to a server?
No. The conversion runs in your browser through a WebAssembly build of FFmpeg. The file is read from your disk into the tab’s memory and written straight back out. Nothing is transmitted.
Can I keep the original quality exactly?
Not through this tool — it always re-encodes. If you need a mathematically identical copy and the codec inside is already H.264 with 4:2:0 chroma, a desktop remux with FFmpeg’s stream-copy mode is the right approach.