MOV and MP4 are close relatives
MP4 was built on Apple's QuickTime file format, the one behind .mov files, so the two containers carry the same ingredients: H.264 or H.265 video and AAC audio. Converting between them usually means lifting those streams out of one wrapper and placing them in another. Nothing is decoded, nothing is compressed again, nothing is lost.
That's why a ten-minute iPhone clip can become an MP4 in a few seconds, and why the new file is almost exactly the same size as the old one. If you were hoping for a smaller file, that's a different job: compress the video instead.
So why convert at all? Because plenty of software only looks for the .mp4 label: upload forms, Android apps, Windows programs and some smart TVs list MP4 as supported and quietly skip MOV, even when they could play what's inside.
iPhone videos: H.265, H.264 and “Most Compatible”
Out of the box, iPhones record in High Efficiency mode, which means H.265 (also called HEVC) video. It packs good-looking footage into small files, but not every device can play it. The alternative, Most Compatible under Settings › Camera › Formats, records H.264 instead.
With Same as original, H.265 video goes into the MP4 as it is. It plays on recent iPhones, Android phones, Macs and current browsers, but some older Windows PCs (which need an extra codec extension from Microsoft), smart TVs and editing apps won't open it. For those, choose High quality: the picture is re-encoded as H.264, which plays practically everywhere.
Expect two things from that re-encode. It takes real time, about as long as the clip plays, often less, and the H.264 file comes out noticeably larger, because H.264 needs more data than H.265 for the same picture. It also needs a browser that can decode H.265: Safari can, and so can Chrome and Edge on most recent Macs and Windows PCs.
Which quality setting to choose
- Same as original, the default, and usually right. Instant, lossless and fine for uploading, archiving or sending to anyone with a recent phone or computer.
- High quality, re-encodes to H.264 with AAC audio. Pick it when someone says the file won't play, or an editing app refuses it.
- Balanced, also H.264, at a lower bitrate. Useful when you want a more compatible file and a smaller one in a single step.
HDR footage, which many recent iPhones record by default, stays HDR when the streams are copied. Re-encoding produces a standard dynamic range version instead, and the converter tells you before that happens.
Files that need a different approach
- Apple ProRes, iPhone Pro models and Final Cut Pro can produce ProRes MOVs. Because browsers generally can't decode ProRes, these can only be rewrapped as MOV or MKV here, not turned into MP4.
- Uncompressed sound, some cameras and recorders store PCM audio in their MOVs. MP4 can't carry it reliably, so the sound is re-encoded as AAC while the picture is still copied.
- Sideways footage, if a clip was recorded with the wrong orientation, rotate it after converting.
- Only part of the clip, trim the video down to the moment you need.
- Not sure what's inside?, Video Info shows the codec, frame rate, bitrate and HDR status of any MOV.