Compressing a video on an iPhone

An iPhone records some of the largest video files of any consumer device, and ships with no way to make one smaller after the fact. Both halves of that are deliberate: the camera is tuned for quality, and Apple's view is that sharing should handle size for you.

Sharing does handle it, which is the problem. Every route out of the phone shrinks the video by its own rules, none of them tell you what they did, and none of them can be told a number.

Why the file is as big as it is

Open Settings, then Camera, then Record Video. The phone lists each mode with the approximate storage it uses per minute. The figures depend on the model, but the shape is always the same: roughly 40MB a minute at 720p, 60–90MB at 1080p, 150–200MB at 4K/30, and 400MB or more at 4K/60.

Two settings on that screen decide most of it:

Resolution and frame rate. 4K at 60 fps is the largest option and, on many recent models, the default. It is eight times the pixels-per-second of 1080p/30. How many megabytes a minute of each mode costs is worth a look before changing anything, because for most sharing 1080p/30 is indistinguishable.

Formats: High Efficiency versus Most Compatible. High Efficiency records HEVC (H.265), which is about half the size of H.264 at the same quality. Most Compatible records H.264, which plays everywhere but doubles the file. Leave it on High Efficiency unless something you upload to regularly rejects HEVC; the phone converts on the way out when it knows the destination needs it.

What each built-in route does to the video

Route	What happens	Can you choose the size?
iMessage	Re-encodes to a lower quality for anything over a few MB; "Low Quality Image Mode" affects photos, not video	No
Mail	Offers Small / Medium / Large / Actual Size for photos; for video there is no such choice, and anything over the account's attachment limit is simply refused	No
AirDrop	Sends the original file, unchanged	Not needed
WhatsApp (as video)	Re-encodes hard, and caps at 16MB	No
Files app, "Compress"	Makes a .zip, which saves about 1% on a video	No
Photos, Edit	Trims length only; no quality or resolution control	No

Trimming is the one real lever Photos gives you, and it is a good one: a 30-second clip trimmed to the 8 seconds that matter is 27% of the size with no quality loss at all. Do that first, always.

What none of the routes offer is the thing an upload form needs: a file under a stated number of bytes, at the best quality that number allows.

Hitting an exact size on the phone itself

Safari on iOS 16.4 and later supports the video half of the WebCodecs API, which means a web page can use the iPhone's own hardware encoder directly. No upload, no app from the App Store, and the encode runs at hardware speed rather than through a server queue.

So the procedure is:

1. Open the compressor in Safari and tap the drop zone. iOS opens the photo picker.
2. Pick the video. A High Efficiency (HEVC) recording is fine: Safari decodes it natively, and the output is H.264 either way, because that is what every destination plays.
3. Set the target. 16MB for WhatsApp, 20MB for Discord, 100MB for a Teams chat or any number you have been given.
4. Wait. A one-minute 1080p clip takes a few seconds; 4K takes longer, because the decode is the expensive half.
5. Save the result to Files or to Photos from the share sheet.

The tool predicts the bitrate the target allows, picks the highest resolution that bitrate can carry, encodes, and then measures the file it produced. If the encoder came in over, it re-encodes on a corrected bitrate, so the file you save is under the number rather than approximately near it.

Two honest caveats. A phone's browser has less memory than a laptop's, so a 4K video over ten minutes long may fail to decode in Safari; trim it first or use a computer. And Safari before 16.4 (any iPhone that cannot update past iOS 15) does not have the encoder API, and the page will say so rather than attempt it.

The arithmetic for the common case

A 48-second 4K/60 clip from a recent iPhone, 310MB, needed under 16MB for WhatsApp:

Budget:    16,000,000 bytes x 8 / 48 s   = 2.67 Mbps
Minus a safety margin for encoder overshoot: ~2.4 Mbps

4K at 2.4 Mbps:    unwatchable, far below the floor
1080p at 2.4 Mbps: soft in motion, acceptable
720p at 2.4 Mbps:  clean

The right answer is 720p, and it will look better on the recipient's phone than 1080p squeezed to the same bitrate. The tool makes that call from the same table; where the floor sits for each resolution is the reasoning.

Sending the same clip through WhatsApp's own compressor would also land under 16MB, at whatever quality WhatsApp decided. Sending it as a document skips the re-encode entirely, which only helps if the file is already under the document limit.

When to change the camera setting instead

If you compress videos from this phone every week, the fix is upstream. 1080p at 30 fps is about a quarter the size of 4K/60, and for anything watched on a phone or in a chat it is the same picture. The 4K original matters for a television, a crop in editing, or an archive, and if none of those apply you are paying storage and time for pixels nobody will see.

FAQ

How do I reduce the size of a video on my iPhone?

Trim it in Photos first, which is lossless. Then either let the sharing route compress it (iMessage, Mail and WhatsApp all do, silently and without a size control) or, for an exact target, open a browser-based compressor in Safari: iOS 16.4 and later expose the hardware encoder to web pages, so the video is re-encoded on the phone without being uploaded or installing anything.

Why is my iPhone video so large?

Because the default record mode on recent models is 4K, often at 60 frames per second, and the phone encodes in real time at a generous bitrate. That is 150–400MB per minute. Switching Settings, Camera, Record Video to 1080p at 30 fps cuts it to around a quarter with no visible difference on a phone or in a chat app.

Can I compress a video on iPhone without an app?

Yes. Safari on iOS 16.4 and later supports the WebCodecs video API, which lets a web page use the iPhone's own hardware encoder. A browser-based compressor therefore runs entirely on the phone, with nothing uploaded and nothing installed. Older iPhones stuck on iOS 15 do not have the API, and a page that needs it should say so.

Does iMessage compress videos?

Yes, for anything beyond a few megabytes, and it does not say by how much or let you choose. AirDrop is the only built-in route that sends the original unchanged. If the recipient is not on an Apple device, re-encoding the video to a stated target yourself gives a predictable result rather than whatever iMessage or the carrier picked.