Two ways to compress
To a file size is for limits: an upload form that refuses files over 25 MB, Discord's free limit, an email attachment. The tool divides the size by the duration to get the bitrate, sets aside a little for the sound and the file's own structure, and picks the largest resolution that will still look decent at that bitrate. You see the plan (resolution, frame rate, bitrate and estimated size) before you start, and the actual size afterwards.
To a quality level is for when you just want a smaller file. Like the quality slider in HandBrake, it asks the encoder for a level of quality and lets the size follow from the content. A quiet talking-head video comes out small; a busy action clip at the same setting comes out larger.
What decides a video's file size
A video file is mostly its bitrate (how many bits are spent per second) multiplied by its duration. A 2-minute clip at 2 megabits per second is about 2 × 120 ÷ 8 = 30 MB, plus the sound. Everything else matters only through the bitrate it needs to look good:
- Resolution. 1080p has 2.25 times the pixels of 720p, so it needs roughly twice the bitrate for the same sharpness. Below a certain bitrate, a smaller resolution looks better than a blocky big one, which is why the automatic setting steps down.
- Frame rate. 60 fps needs more bitrate than 30 fps; for talking, screen recordings and most phone clips, 30 or even 24 fps is plenty.
- Movement and detail. A static screen recording compresses far better than handheld footage of a crowd, confetti or water. Two videos of the same length and settings can differ several-fold in size.
- Codec. H.264 plays everywhere. VP9, HEVC (H.265) and AV1 give the same quality in 30 to 50% fewer bits but are not supported by every player or upload form.
- Sound. Usually small: 96 kbps stereo is about 0.7 MB a minute. Removing it helps only for very small targets.
Choosing settings
- Resolution: automatic drops to 720p, 540p or lower only when the bitrate would otherwise be too thin. Choose "Keep the original" if the people receiving it need full resolution and you can accept a lower quality, or pick 720p for anything watched on a phone.
- Frame rate: phone videos are often 60 fps. Capping at 30 fps saves a good share of the bitrate with little visible difference for most content.
- Sound: 96 kbps is fine for speech and most music on phone speakers. Use 64 kbps for tight targets, or remove the sound for screen recordings without narration.
Platform limits
The target list includes common limits with a small safety margin: Discord's free upload limit, email attachments and WhatsApp. Platforms change their limits, so each is listed with its source in the sources section below. There are dedicated pages for Discord, email and WhatsApp with the details.
Why it is slower than a desktop app, and when to use HandBrake
This tool uses your browser's own video encoders through WebCodecs, often the same hardware encoders a desktop app would use, but it runs inside a browser tab with a fraction of the computer's memory and without the tuned encoders desktop apps ship. Short clips are quick; a 10-minute 1080p video can take several minutes on a laptop and longer on a phone. The tool refuses files that are likely to run out of memory rather than failing halfway. For long videos, 4K footage, batches of large files, or precise control over the encoder, use HandBrake, which is free, open-source and much faster for heavy work.
Browser support and troubleshooting
The line at the top of the tool lists the video and audio codecs this browser can encode. Current Chrome and Edge on Windows and Mac handle H.264, VP9 and AV1 with AAC and Opus; Safari adds HEVC; Firefox supports WebCodecs from version 130. If a file will not open:
- "This browser cannot decode…" usually means HEVC (H.265) video, common from iPhones, in a browser without HEVC support. Try Safari or Edge on a computer with hardware HEVC, or convert it on the phone (Settings › Camera › Formats › Most Compatible for future videos).
- "Cannot read this file's format" means an old or unusual container such as AVI, WMV or FLV that browsers cannot read. Convert it with HandBrake first.
- It stops or the tab reloads on long or 4K videos: the tab ran out of memory. Trim the video into parts, close other tabs, or use a desktop app.
- Very slow on a phone or an older laptop: the browser may be using software encoding. Shorter clips and lower resolutions help.
A worked example
A 90-second 1080p phone video at 60 fps is 180 MB. To send it on Discord's free plan (20 MB), the tool targets 19 MB: 19 MB over 90 seconds is about 1.7 Mbps in total; take away 96 kbps for sound and 3% for the file structure and about 1.55 Mbps is left for the picture. At 1080p and 60 fps that is too thin, so with the frame rate capped at 30 fps the automatic setting picks 720p, where 1.55 Mbps looks clean. The estimate shows 18.9 MB; the result usually lands within a few percent, and if it lands over, the tool tries again at a corrected bitrate.
Privacy
Your video never leaves your device. It is read and written in the browser tab; there is no upload, no server-side processing and no account. You can disconnect from the internet after the page has loaded and it still works. Free use has no watermark and covers files up to 500 MB and 10 minutes; the A$9 lifetime licence removes those limits (your device's memory still applies), queues up to 20 files and saves presets.