Video Compressor
Video bitrate for a target size = target MB x 8,000 / seconds / 1.02 - audio kbps. A 60 second clip compressed to 8 MB with 96 kbps audio gets about 950 kbps of video. This compressor does the math and encodes to MP4 (H.264) or WebM in your browser, with no upload.
How to use
- Drop a video onto the box or press it to choose one (MP4, MOV, WebM, MKV and most other formats). Its size, length and resolution appear.
- Choose File size and type the size you need, for example 8 MB for a chat app limit, or choose Quality (CRF) to keep a steady quality. Pick MP4 or WebM, the audio bitrate and, if you like, a lower maximum height such as 720p.
- Press Compress video. The first time, the converter engine is downloaded once. Progress is shown while it encodes. When it is done, play the result, compare the sizes and download it.
How it works
In File size mode the video bitrate comes from the target: video kbps = target MB x 8,000 / seconds / 1.02 - audio kbps. The 2% covers the MP4 or WebM container. A 60 second clip with an 8 MB target and 96 kbps audio gets about 950 kbps of video. This is the same formula as the video bitrate calculator on this site.
In Quality mode the encoder uses CRF (constant rate factor): it keeps the picture quality steady and lets the size follow the content. For MP4 (H.264) the range is 18 to 40, where 23 is close to the original look and every +6 roughly halves the size. For WebM (VP8) the range is 4 to 50.
Encoding runs with FFmpeg compiled to WebAssembly on one CPU core, with the fastest presets (x264 veryfast, VP8 realtime). It is slower than desktop apps: on a recent laptop a 720p clip takes about as long as it plays, or longer. Lowering the height to 720p or 480p speeds it up and saves the most space.
FAQ
Is my video uploaded?
No. The video is read and encoded inside this browser tab. The only download is the converter engine from this site. No upload, no account and no watermark.
Why is the result a little bigger or smaller than my target?
The encoder aims at an average bitrate in one pass, so simple scenes come out smaller and busy scenes a bit larger. Expect the result within about 10% of the target. If it must stay under a hard limit, aim 10% lower.
Should I choose MP4 or WebM?
MP4 with H.264 plays almost everywhere, including phones, chat apps and editors, so it is the safe choice. WebM with VP8 is for web pages and browsers. It is open but is not accepted by every app.
How small can I make a video?
The tool needs at least 50 kbps for the picture after the audio is taken out. For a very small target, lower the audio bitrate and the height. As a guide, 480p looks acceptable from about 500 kbps, 720p from about 1,500 kbps.
Does it work on a phone?
Yes, in a recent browser, but encoding on a phone is slow and the tab has less memory, especially on iPhone and iPad (Safari 16.4 or later). Short clips work best. Keep the tab open until it finishes.