You shoot a video on your iPhone. You send it to a colleague on Windows. They reply: "I can't open this." You've seen this before, or you're seeing it for the first time right now. Either way, the fix is the same.
The file is in MOV format. That's the problem.
Why Apple uses MOV
MOV has been Apple's native video container since the QuickTime days in the early 1990s. It handles H.264, HEVC, multiple audio tracks, chapter markers, and a lot of metadata that Apple's own apps know what to do with. Inside the Apple ecosystem, it's well-supported. iCloud, Final Cut Pro, iMovie, Photos — they all speak MOV natively.
The issue is that "Apple's ecosystem" ends at the edge of Apple devices. Everywhere else, MOV support ranges from inconsistent to nonexistent.
What actually breaks
On Windows, there's no built-in MOV support. File Explorer won't generate thumbnails. Windows Media Player won't play it. VLC can, but you can't assume your recipient has VLC installed. The file lands on their desktop and just sits there, useless.
On Android, the situation is worse. Share a MOV to an Android user and their phone downloads a file with no default app to open it. It doesn't fail gracefully — it just doesn't open.
Web platforms are where most people hit the wall. Instagram's web uploader is MP4-only. Slack previews MOV only on Apple devices; a Windows or Android user on the other end sees nothing. Google Drive and Dropbox both require MOV files to be downloaded before viewing — there's no inline playback. YouTube accepts MOV, but processing takes longer.
Non-Apple video editors are a mixed bag. Premiere and DaVinci Resolve handle MOV fine. Plenty of browser-based and lightweight editors don't — they accept the upload, then silently produce no output.
The conversion itself
Here's the part worth understanding: converting MOV to MP4 is usually just a container swap. The video inside your MOV is almost certainly encoded with H.264, and MP4 supports H.264 too. So the converter just moves the data from one container to the other without touching the actual video frames.
No re-encoding means no quality loss. The image you recorded is the image you get out.
The exception is ProRes — if you're shooting ProRes on an iPhone Pro or a professional camera, the codec doesn't map cleanly into MP4. In that case the converter will actually re-encode the video. It's slower, and there's some processing involved, but the output is still a usable, compatible file.
For the vast majority of iPhone videos, though, it's a straight remux. Fast, lossless, done.
File size
One side effect: MP4 files tend to come out smaller. iPhone MOV files are often encoded at higher bitrates with more container overhead.
| Format | Typical size (1 min, 1080p) |
|---|---|
| MOV (from iPhone) | 150–220 MB |
| MP4 (converted) | 80–180 MB |
Same visual quality. The reduction comes from how the container handles metadata, not from compression artifacts. If you're attaching video to an email or sharing over a slow connection, the difference matters.
When to convert, when not to
Convert when you're sharing with anyone outside the Apple world, uploading to a web platform, or storing video somewhere you might need to access in five years on an unknown device. MP4 is about as universal as video formats get. It plays in every browser, on every major platform, without plugins.
Keep the MOV if your entire workflow stays within Apple tools. iPhone to iCloud to Final Cut Pro — in that chain, MOV carries metadata that actually gets used. There's no compatibility problem to solve, so converting just adds a step with no benefit.
If you're doing serious color work in ProRes, keep the MOV there too. ProRes in an MP4 container is technically possible but unusual, and professional editing software expects the MOV wrapper for that codec.
For everything else — the family video you're uploading, the screen recording you're sharing with a coworker, the clip you're posting — convert it. It takes a few seconds, and it eliminates an entire category of "why won't this open" messages you'd otherwise have to troubleshoot later.