A forty-second clip off an iPhone can be 250 MB, and it is reasonable to assume something has gone wrong. Nothing has. Here is where the bytes go, and what to do about it.
iPhone video size per minute, from Apple
You do not have to take anyone’s word for this. Open Settings, go to Camera, then Record Video, and the iPhone lists its own storage cost per minute for each mode. The first column is the default, High Efficiency (HEVC); the second is what the same minute costs with Settings → Camera → Formats set to Most Compatible (H.264). The figures vary a little between models and iOS versions, but they are about:
| Recording mode | High Efficiency (HEVC) | Most Compatible (H.264) |
|---|---|---|
| 720p at 30 fps | 40 MB | 60 MB |
| 1080p at 30 fps | 60 MB | 130 MB |
| 1080p at 60 fps | 90 MB | 175 MB |
| 4K at 24 fps | 135 MB | 270 MB |
| 4K at 30 fps | 170 MB | 350 MB |
| 4K at 60 fps | 400 MB | HEVC only |
Apple shows figures for the phone in your hand, so an older or newer model can differ a little. ProRes, on the Pro models, is in a different league altogether and has its own section below.
The bottom row is the answer to most of these questions. 4K60 is nearly seven times the storage of 1080p30, and it is not an unusual setting to have selected — plenty of phones ship on a high setting or get changed to one once and never changed back.
Two things drive the difference. Resolution: a 4K frame is 8.3 million pixels against 1080p’s 2.07 million, four times as many. Frame rate: 60 fps is twice the frames of 30. Multiply them and 4K60 is eight times the raw pixel throughput of 1080p30.
Phones deliberately spend a generous bitrate
A phone encoding video is in an unusual position. It has milliseconds per frame to make decisions, it is running on a battery, it is thermally constrained, and — most importantly — it is capturing something that cannot be re-shot.
Given those constraints, the sensible engineering choice is to err heavily toward spending bits. A slightly larger file is a recoverable problem; a moment recorded badly is not. So a phone uses fast encoder settings and a high bitrate, where a compressor with unlimited time would think harder and spend less.
That is exactly why iPhone footage compresses so well afterwards. There is a great deal of slack in it, and removing that slack is nearly free in terms of visible quality.
HEVC, and why the file will not open on Android
Since iOS 11, iPhones default to recording HEVC — H.265 — rather than H.264. It is the better codec, and it is why a 4K60 minute is 400 MB instead of considerably more.
The cost is compatibility. HEVC decoding is not universal: plenty of Android devices, older computers, web applications and editing tools will give you a black frame, audio with no picture, or a flat refusal. This is far and away the most common reason someone reports that an iPhone video “will not open” on a friend’s phone.
There are two fixes. Ahead of time, in Settings → Camera → Formats, choose Most Compatible — the phone then records H.264 instead, at roughly twice the file size for the same quality, as the second column of the table shows. After the fact, re-encode: compressing to MP4 in this tool with the codec left on H.264 fixes compatibility and shrinks the file in the same pass. The tool will also write H.265 if you ask it to, which keeps the footage in the generation it was shot in and keeps the problem this section is about, so save that for files staying on your own Apple hardware.
ProRes is a different order of magnitude
If you have a Pro model and have turned on ProRes recording, the arithmetic changes completely. A minute of ProRes runs to around 1.7 GB at 1080p and roughly 6 GB at 4K, and Apple itself warns that ProRes files can be up to 30 times larger than HEVC.
That is not a defect either. ProRes is an intermediate codec designed for editing rather than delivery: it barely compresses on purpose, so that every frame decodes independently, scrubbing is instant, and colour grading has real information to work with. It is the right format to shoot in if you are going to grade the footage, and the wrong format to send to anybody.
Compressing a ProRes file to H.264 routinely reduces it by 95% or more with no meaningful visible loss, because you are converting an editing format into a delivery format — which is what it was always meant to become.
Why the file is also a MOV
iPhones record into a QuickTime container, which is where the .mov extension comes from. The container is not why the file is large — the codec and the bitrate are — but it does affect where the file will play, since some tools handle MP4 more happily than MOV.
MP4 was standardised from the QuickTime format, so the two are structurally close relatives. If your MOV already contains H.264, converting it to MP4 is a remux: the video stream is copied bit for bit into a new wrapper and the job finishes in seconds with zero quality loss. It does not make the file smaller, and that is the point — use it when the problem is “this will not play here”, not when the problem is “this is too big”.
Making an iPhone video smaller
In rough order of how much they help:
- Drop the resolution. 4K footage almost never needs to stay 4K. Going to 1080p removes three quarters of the pixels before the encoder starts, which beats any bitrate setting.
- Re-encode with a real compressor. The phone’s fast encoder left a lot on the table. A proper encode at a sensible bitrate typically halves the file with nothing visible lost.
- Trim it. File size is bitrate times duration, and duration is the term nobody thinks to reduce. Most clips have a shorter version that is better anyway, and the compressor takes a start and an end point so you can make the cut in the same run as the encode.
- Reconsider 60 fps. Unless the subject is fast-moving or you plan to slow it down, 30 fps costs half as much and looks the same.
None of this needs a computer. The compressor on this site runs in Safari, so you can compress the video on your iPhone without installing an app, within the limits of what a phone’s memory allows.
If you are compressing for a specific destination there are pages for the common ones: 16 MB for WhatsApp, 20 MB for email, or any ceiling you like. All of it runs in your browser — the video is never uploaded anywhere, which matters more than usual for phone footage, since phone footage is where people’s actual lives are.
Related reading
- Compress a MOV file — the format-specific page, including remuxing.
- H.264 vs H.265 — what HEVC buys and what it costs.
- What is video bitrate? — the number underneath all of these figures.
- Reduce video size without losing quality — technique by content type.