Video is the file type that surprises people most. A photo is a few megabytes and nobody thinks about it. A minute of video from a recent phone can be several hundred, and the first time you try to attach it to an email the number suddenly matters. The replies people get online are a scatter of apps, settings and tips, some of which are right for their situation and some of which waste an evening.
This post goes through what people actually ask, does the arithmetic that explains why the files are so big, separates the cases where you should not compress at all from the cases where you should, and then shows measured results from shrinking a real 4K clip, including how long it took and what it cost in quality.
What people actually run into
These are real threads from the Apple Community forums, summarised in our own words with a link to each. Usernames are left out. The forum software and phone menus have moved on since some of them were written, so take the specifics as a record of the problem.
“reduce video file size before sending email”
- The problem
- The poster wanted to shrink a video inside the Photos app so it could be sent by email.
- What they tried
- The post does not say.
- What happened
- One reply suggested Mail Drop, which sends a link instead of the file, and said shrinking video is not really practical because it costs quality. The other warned that some mail servers cap attachments at around 10 MB, so even a compressed copy might not fit, and suggested a file sharing link instead.
“How to compress iPhone videos?”
- The problem
- A 39 second video had become a file of more than 274 MB, far too large to email, and the poster wanted it smaller without losing quality.
- What they tried
- The post does not say.
- What happened
- One reply said most email systems reject files over about 20 MB and doubted any utility could shrink it that far, suggesting a file transfer site. The other suggested exporting at a lower resolution such as 720p, and noted that newer video formats take up more storage.
“how to compress a video in photos”
- The problem
- A video recorded on an iPad and moved to a Mac needed to be shrunk so it could go by email.
- What they tried
- The post does not say.
- What happened
- AirDrop was suggested, since it avoids compression, and the poster replied that it was not an option because the video had to be emailed. Compression apps were also named, with a warning that free ones may show adverts.
“Emailing larger video files”
- The problem
- Videos would not send by email. The phone said the files were over 100 MB and asked for Wi-Fi, even though it was on home Wi-Fi.
- What they tried
- Turning off cellular data, and planning to split the videos into several smaller emails.
- What happened
- Replies suggested Mail Drop and sharing links, noted that most email providers cap attachments somewhere between 10 and 30 MB, and offered a zip file, which would not help a 100 MB video. The poster planned to send from a Windows computer instead.
“iPhone videos file size too large to email”
- The problem
- A video of under one minute, recorded on an iPhone 13 mini, was too large to send through a webmail account.
- What they tried
- Turning off HDR recording, which did not shrink it enough.
- What happened
- The single reply recommended Mail Drop, which uploads the video to iCloud and emails a download link, for files up to 5 GB. The thread is closed.
Across seven years and several devices the same two answers keep coming back: send a link instead of a file, or make the file smaller. Both are right, in different situations, and the threads rarely say which situation is which. They also share a blind spot. Nobody does the arithmetic, so nobody knows how much smaller the file has to get, or what that will cost.
The arithmetic that explains it
A video file is just a rate multiplied by a length. The rate is the number of bits per second the video uses, and the length is how many seconds it runs. Everything else follows from that.
That last number is why people feel stuck. Turning the quality slider down a little might halve a file. Fitting a 4K clip into an email needs something close to a thirtieth. The way to get there is to change the picture size as well. A 4K frame holds four times the pixels of a 1080p frame and nine times those of a 720p one, and most of the weight sits in those pixels.
First decide whether you should shrink it at all
The threads quietly make the point that shrinking is the lesser option when the goal is simply to get the video to a person. Shrinking costs quality and takes time. Sending a link costs neither.
- The person is nearby. AirDrop sends the original at full quality with no limit worth worrying about.
- The person has an email address and nothing more is needed. A share link from iCloud, Google Drive, Dropbox or OneDrive in the message means the original arrives untouched. On an iPhone, Mail Drop does this for you when an attachment is too large.
- The place has a hard limit. A form, a job portal, a chat app or a school system that will not take anything over a stated size. A link may not be accepted, so the file itself must be smaller.
- The recipient needs a file they can keep and edit. Sometimes a compressed copy is fine. Sometimes it is not, and you should send the original some other way.
What shrinking does, with measured numbers
To put real numbers on it, we made a 20 second 4K test clip that mimics a phone video, in the same format and at a similar rate. It came to 89.7 MB at about 37 Mbit/s. We then shrank it with the settings our Compress video tool uses and measured each result.
Same clip, different choices
The test clip is smooth landscape footage in HEVC at 3840 by 2160, 30 frames a second, with audio. Smooth footage compresses well, and busy handheld or fast action footage will give larger results, so treat these as a best case. The 720p result at quality 24 was produced in the browser by our tool and matched a desktop run of the same settings to within 0.1 MB. The other results come from the same encoder settings run on a desktop. Quality 24 is the tool's Balanced setting and 28 is Smaller file.
Two lessons stand out. Dropping from 4K to 720p did far more than any quality setting could. Keeping the full 4K size and only raising the compression still left the file at nearly 19 MB, which would miss most email limits. And the large reduction that one reply in the 2021 thread doubted is realistic, as long as you are willing to accept a smaller picture. For a video that will be watched on a phone or a laptop, 720p is rarely a loss anyone notices.
How long it takes, and the limits
A browser tool is slower than a desktop app, and it is better to know that in advance. Our tool does the work with ffmpeg compiled to WebAssembly, on one processor core, inside the tab. For the test clip it took 82 seconds to process 20 seconds of 4K HEVC, a little over four times real time. A 39 second clip like the one in the thread would take close to three minutes. A short 1080p clip is much quicker.
- Keep the tab open and the device awake while it runs. Closing the tab stops the job.
- Very long or very large videos strain memory. The tool warns when a file is large, and a phone has far less room to work in than a computer.
- 4K HEVC is the slow case. Older or smaller video converts faster.
- Busy footage will not shrink as far as our smooth test clip did.
Stopping it happening next time
Most of the pain comes from recording everything at the highest setting by default. That is a fine choice for footage you want to keep forever and a poor one for a clip whose whole purpose is to be sent to someone. The size arithmetic works in your favour here, because every step down in picture size removes a large share of the data before any compression happens.
- Record shareable clips at a lower setting. The phone's camera settings let you choose the resolution and frame rate for video. A clip at 1080p and 30 frames a second carries a small fraction of the data of 4K at 60, which is roughly eight times the pixels per second.
- Keep 4K for the moments that matter. Birthdays and trips you will want to watch on a big screen in ten years. Everyday clips rarely need it.
- Mind the format if the other end is a Windows computer. Newer phone videos use a modern codec that some Windows setups cannot play without extras. A copy converted to the older, universal MP4 format avoids that, and it is another case where a conversion is the right answer and a link is not.
- Trim before you send. Cutting dead time from the start and end shrinks the file in direct proportion, with no quality loss at all, because size is rate multiplied by length.
Fitting a specific limit
When a place states a number, working to that number beats guessing a quality setting. The method is to take the limit, leave a margin for the container, subtract the audio, and spend what is left on the picture across the length of the clip. For a 39 second video and a 10 MB limit, that leaves a video rate of about 1.8 Mbit/s, which at 720p is perfectly watchable. We checked the method on the test clip: asked to stay under 10 MB, the 20 second video came out at 9.2 MB, which is under the limit with a little margin, and it took about a minute and a half.
Compress videoPick a quality, or choose a size limit such as 10 or 25 MB and it works out the rate for you. It runs on your device, so the video is not uploaded.Things people suggest that do not help
- Zipping the video. A video is already compressed, so a zip file saves almost nothing, as one thread above notes.
- Turning off HDR alone. It helps a little, but in the 2025 thread it did not bring the clip under the limit.
- Splitting into several emails. It works, but the recipient then has to join the pieces, and many providers limit the total as well.
- Compressing twice. Each pass loses more detail. Go back to the original and choose the setting once.
- Free apps that add a watermark or adverts. Check what you are agreeing to, and that the file is not uploaded somewhere.
A short routine to keep
Ask whether a link will do. If it will, send one and keep the original. If the file itself has to be smaller, find out the exact limit, drop the resolution to 720p first, and only then adjust quality. Watch the result before you send it, and keep the original. For anything private, use a tool that does the work on your own device.
Questions people ask
Because it is recorded at high resolution and a high rate. A 4K clip at 30 frames a second can use 30 to 60 megabits every second, which is around 4 to 7 MB for each second of video. A minute can be several hundred megabytes.
It varies by provider, and the threads put it between roughly 10 and 30 MB. Check the limit of the account you are sending from and the one you are sending to, and leave some margin.
Usually, when you can. A link keeps the original quality and costs nothing. Compress only when the place you are sending to insists on a smaller file, such as an upload form with a hard limit.
720p is a sensible default for watching on a phone or laptop, and it gives the biggest saving. Use 1080p if the video will be shown on a large screen. Use 480p or lower only when a limit demands it.
Not with a tool that runs in your browser. Ours does the work on your own device, so the video never leaves it. Many online compressors do upload the file, which matters for anything private.