What makes a video file big?
A video's size is almost entirely its bitrate multiplied by its length. Bitrate is how many megabits the encoder spends on each second. Phones are generous: an iPhone records 1080p at about 16 Mbps in H.264 and 4K at around 45 Mbps. That is far more than anyone needs to watch on a phone screen or in a chat, and it's why a one-minute clip can weigh 130 MB.
Compression lowers the bitrate (and, if you choose, the resolution) while keeping what the eye notices. Modern encoders are good at spending bits where they matter, on faces, edges and motion, and saving them on flat walls, skies and still backgrounds.
The three settings, and when to use each
All three re-encode to H.264 MP4 with AAC audio at 128 kbps, which plays on every device. They differ in resolution and in how hard the encoder squeezes:
- Smallest file caps the shorter side at 720 pixels (720p landscape, 720×1280 portrait) and uses CRF 32. Use it for WhatsApp, Telegram, email, Discord's 10 MB free upload limit, or anything watched on a phone. Typical phone footage shrinks by 85–95%.
- Balanced caps the shorter side at 1080 pixels and uses CRF 28. It's the right default for uploads, cloud storage and sharing with people who might watch on a laptop or TV. Expect 60–85% savings on phone footage.
- High quality keeps the original resolution and uses CRF 23, the encoder's standard visually-transparent setting. Use it for archiving, or for 4K footage you still want in 4K, at around half the size.
What does CRF mean?
CRF, constant rate factor, is the quality knob of the x264 encoder. Lower numbers mean better quality and bigger files. 23 is the encoder's default and is hard to tell from the source on most footage, and every +6 roughly halves the file size. Unlike a fixed bitrate, CRF adapts to the content, so a static talking-head video comes out much smaller than a football match of the same length at the same CRF. That's why two videos of the same length can compress very differently.
Why won't my video get smaller?
If a video has already been compressed, by WhatsApp, a social network, a screen recorder set to a low bitrate or an earlier pass through a compressor, there may be little left to remove. Re-compressing it at a similar quality won't save much and can even make the file slightly bigger, and each extra pass softens the picture a little more.
The tool shows the new size next to the download button, so you can see before saving whether it was worth it. If the saving is small, try Smallest file, which also lowers the resolution, or cut the video to the part you actually need with the Video Cutter. Removing a minute of footage beats any amount of squeezing.
How small does a video need to be for email, WhatsApp or Discord?
Most people compress to get under a specific limit. These are the ones that come up most often:
- Email: Gmail and Yahoo allow 25 MB of attachments per message, and Outlook.com 20 MB. Anything bigger becomes a cloud link.
- Discord: 10 MB per file on the free plan.
- WhatsApp: videos sent as media are re-compressed by WhatsApp itself. Sending a smaller file first gives you control over how it looks, and sending it as a document skips WhatsApp's compression entirely.
- Job portals, school platforms and government forms often cap uploads at 10–100 MB.
How long does compressing a video take?
Compression is a full re-encode and runs in your browser, so the speed depends on your device. A recent laptop handles 1080p at roughly real time or faster with Smallest file, while a phone may take two or three times the video's length. Smaller output settings are faster because there are fewer pixels to encode. Keep the tab open until the progress bar finishes.
In exchange your video never leaves your device. There's no upload, no copy on a server, and no account. That matters for family videos, screen recordings of private documents and anything work-related.