How to use
- Add one or more videos; each shows an estimated output size.
- Choose a target size or a quality preset; optionally lower the resolution, frame rate or audio bitrate.
- Compress and compare the before and after sizes, then download.
Worked example
With a 25 MB target, a 2-minute clip gets 25 MB × 8 ÷ 120 s = 1.75 Mb/s in total; after a 2% container allowance and 128 kb/s audio, the video is encoded at about 1.58 Mb/s (1 MB = 1,048,576 bytes).
Supported formats and limits
| Input | MP4, MOV, WebM, MKV |
|---|---|
| Output | MP4 (H.264, H.265 or AV1 with AAC), WebM (VP9, AV1 or VP8 with Opus) |
| Limits | Input files up to 4 GB; the compressed file is built in memory. Codec availability depends on the browser. Needs a browser with WebCodecs (current Chrome, Edge, Safari 17+ or Firefox 130+). Other browsers are told so before any work starts. |
| Engine | Mediabunny conversion with WebCodecs; bitrate derived from the target size and duration, with a second pass if the first lands above the target |
Limitations
- Target sizes are approximate because encoders vary the bitrate scene by scene. If the first result is over the target, the video is encoded once more at a lower bitrate; very grainy footage can still end up larger, and the tool says so.
- Some platform encoders only accept certain audio bitrates (for example 96 to 192 kb/s for AAC on Windows); the nearest supported one is used and noted.
Questions
Will the file land exactly on my target size?
Close to it, not exactly. The bitrate is worked out from the target and the duration, and encoders vary bitrate scene by scene. If the first result is over the target, the video is encoded again at a lower bitrate; very grainy footage can still end up larger, and the tool says so.
How is the bitrate for a target worked out?
Target size × 8 ÷ duration gives the total bitrate. A 2% container allowance and the audio bitrate are subtracted, and the rest goes to the video.
Which codecs can I use?
H.264, H.265 or AV1 in MP4, and VP9, AV1 or VP8 in WebM, depending on what your browser can encode. The tool checks before it starts.
Privacy
Runs on your device. Files and text are processed in this browser tab and are not uploaded.
See the privacy policy for how toolsdocks handles data.