How to use the video compressor
- Drop a video onto the box or click to choose one.
- Under Aim for, choose A quality level (High, Medium, Low or Very low) or A file size and enter the Target size in MB.
- Pick a Resolution, from Keep resolution down to 360p. 720p is the default.
- Optionally set Frame rate (keep, 30 or 24 fps) and Audio (remove, 64, 96 or 128 kbps).
- Choose an Output format (MP4, WebM, MOV or MKV), press Compress video and download the result.
What it does and when to use it
Phone cameras record at high bitrates, so even short clips can be too big to email, attach to a form, upload to a chat app or store on a nearly full phone. The compressor re-encodes the video with settings you choose so the file gets smaller, and shows how much you saved and the old and new resolution.
Quality mode is the easiest: pick a level and let the encoder decide the bitrate. Size mode is for hard limits, such as an upload form that rejects anything over a certain number of megabytes.
If only part of the clip matters, cut it first with the video trimmer, since a shorter clip needs far fewer bytes. To change only the dimensions, use video resize, and if you only need the sound, the video to audio extractor makes a much smaller file.
How it works
The tool uses Mediabunny (about 0.7 MB, loaded the first time) in a Web Worker to read the file, and your browser’s WebCodecs encoder to compress it again. MP4 output prefers H.264 (AVC); WebM prefers VP9. If the first choice is missing, the tool tries other codecs your browser can encode.
In size mode, the video bitrate is:
video bitrate = (target bytes × 8 × 0.98) ÷ duration in seconds − audio bitrate
The 0.98 leaves 2% for the container’s own data. If the answer is under 50 kbps, the tool refuses rather than producing an unwatchable video, and suggests a larger target or removing the audio.
Resolution presets set the short side of the frame, so a portrait clip at 720p becomes 720 pixels wide. Videos are never enlarged.
Worked examples
These bitrates come from the tool’s own size formula.
An 8 MB target for a 60-second clip with 96 kbps audio gives a video bitrate of 1,000,111 bps, about 1,000 kbps. At 720p that is often acceptable for talking-head or casual footage.
A 25 MB target for a 3-minute clip with 96 kbps audio gives about 1,046 kbps for the video.
An 8 MB target for a 10-minute clip leaves only about 14 kbps, under the 50 kbps floor, so the tool asks for a larger target instead.
Limits and tips
- Re-encoding takes time, especially for long clips on phones. A progress bar shows how far it has got, and you can cancel at any point.
- WebCodecs is required. Use a current desktop Chrome, Edge, Firefox or Safari, or Chrome on Android.
- Long or 4K files use a lot of memory because the output is assembled in the tab.
- Compressing twice loses quality twice. Start from the original file each time you try new settings.
Frequently asked questions
How do I compress a video to a specific size?
Which setting saves the most space?
Why is my compressed video not smaller?
Will the quality drop?
Is my video uploaded?
How do we know nothing is uploaded? Test it yourself on the privacy proof page.