How to compress a video without losing quality
Most phone video is recorded at a far higher bitrate than the screen needs. Here is what to change, and what actually loses quality.
Why phone video files are so big
A phone records 1080p video at roughly 16 megabits per second and 4K at far more, because it is optimized to look good straight out of the camera, not to be small. A one-minute clip easily passes 100 MB at that rate. Almost none of that bitrate is visible on a phone or laptop screen: encoding the same footage at a quarter or a fifth of the bitrate is very hard to tell apart from the original on anything but a large, calibrated display.
What actually controls the trade-off
Three settings decide the result: bitrate (how much data per second of video; lower it and the file shrinks roughly proportionally), resolution (a 1080p clip has four times the pixels of 540p, so downscaling saves a lot before any perceptible loss), and codec (H.264 is universal, but H.265/AV1 fit the same quality into a smaller file if the destination supports them). Cutting bitrate too far causes blocky compression artefacts in fast motion; cutting resolution first, then bitrate, usually looks better than dropping bitrate alone.
On an iPhone
There is no in-app "compress" button, but Mail does it for you: attach the video in Mail and tap the size options that appear (Small, Medium, Large, Actual Size) before sending — Small and Medium re-encode the video at a lower bitrate and resolution. To shrink files you record from now on, go to Settings, Camera, Record Video, and pick a lower resolution or frame rate; this does not affect videos already on your phone.
On Android
Android has no built-in compressor either. Sending a video through WhatsApp, Google Messages or similar apps re-encodes it at a lower bitrate automatically, which works as a rough compressor if you do not need the original attached anywhere.
On Windows
Clipchamp comes preinstalled with Windows 11: open it, import the clip, and use the export step's quality presets (720p or 1080p, and a bitrate/quality slider) to control the size before saving.
On a Mac
QuickTime Player can re-export at a lower resolution: open the file, then File, Export As, and choose 1080p, 720p or 480p instead of the original size. This reduces resolution, not bitrate directly, but it is a real, built-in way to shrink a file.
Compressing to an exact target
Stayput's video compressor re-encodes the file in your browser tab and lets you pick a quality level or a target file size. The Discord preset aims for Discord's 10 MB upload limit, and the email preset aims for 25 MB, both re-encoding automatically until the file fits. Nothing is uploaded to do this: the encoding runs on your device.
Questions
Does lowering the resolution always look worse?
On a small screen (phone, chat preview) it is often invisible, since the display cannot show the extra detail anyway. It matters more if the video will be viewed full-screen on a large display.
Should I lower bitrate or resolution first?
Resolution first for a big size cut with the least visible loss, then bitrate to fine-tune. Cutting bitrate alone on a high-resolution video tends to show blocky artefacts sooner.
Why does a re-compressed video sometimes look worse than the original even at a similar size?
Re-encoding an already-compressed video is lossy on top of lossy. Compressing straight from the original file, rather than a copy that has already been re-saved once, keeps more quality at the same target size.
What is a reasonable size for a 30-second phone video?
At a bitrate most people cannot distinguish from the original, a 30-second 1080p clip typically compresses to somewhere between 3 and 8 MB, well under most upload limits.