How much smaller will my video get?

The estimate under the button says, and it updates as you change the settings. A phone records 1080p at around 17 Mbps and the balanced setting asks for 5.5, so footage straight off a phone usually lands near a third of its original size.

Will compressing it twice make it worse?

Yes. Each encode discards detail the next one cannot recover, so compressing an already compressed copy loses a second layer. Going back to the original and compressing once is always better than compressing the compressed version again.

Is my video uploaded anywhere?

No. It is decoded and re-encoded by your own browser and never leaves the machine. There is no server in this, which is also why the speed depends on your computer rather than on how busy a website is.

Why does the sound say it is being copied?

Because that is the default, and it is the better choice. The audio in a video has already been through an encoder once, and putting it through a second one for no reason loses a little more of it. Pick a bitrate instead if the sound itself needs to be smaller.

Can I compress a video on my phone?

Yes, if the browser is a recent Chrome or Safari, and a short clip is the sensible thing to try first. Phones have the same hardware encoders, though a long 4K video will warm the device up and may run out of memory before it finishes.

Compress Video

Re-encodes a video at a lower bitrate so the file comes out smaller. The figure under the button is the estimate, and it moves as you change the settings. You can also give it a size in megabytes to aim for and let it work the bitrate out backwards.

Choose a video or drop it hereMP4, MOV, WebM or MKV, up to 500 MB.

Runs entirely in your browser. Your files are never uploaded.

How to use Compress Video

1Choose a video, or drag it onto the box.
2Pick a quality, or type a size in MB to aim for.
3Drop the resolution too if the file has to get much smaller.
4Press compress, then download the result.

Where the size goes

A video's size is its bitrate multiplied by its length and almost nothing else. Bitrate is how many bits a second the encoder may spend on the pictures, so halving it halves the file, and no setting on this page gets around that arithmetic.

Which is why the quality setting is worth trying before the resolution. A 1080p clip at a lower bitrate usually looks better than the same clip shrunk to 480p and given a high one, because the encoder gets to choose where the detail goes instead of having three quarters of the pixels thrown away in advance.

Resolution earns its place when the drop has to be large. Moving from 1080p to 720p removes over half the pixels, and 720p needs about half the bitrate, so the two together take a file to roughly a fifth of its size and still look right on a phone.

Aiming for a size

Type a number of megabytes and the bitrate is worked out backwards from it. The length, the sound and about two percent of container overhead come off the top, and whatever is left is what the pictures get. Encoders hold that figure closely, so the result lands within a few percent of what you asked for.

There is a floor, at around 120 kbps, below which the picture stops being worth looking at. A target that would need less than that is not accepted quietly: the page says what the file will really come out as, so a two-minute clip does not silently fail to be 1 MB.

Most targets come from a limit somewhere else. 25 MB is the ceiling on a Gmail attachment, 16 MB on a WhatsApp video, and plenty of contact forms stop at 10. Removing the sound helps more than people expect at short lengths, since 128 kbps of audio is a quarter of the budget in a 10 MB minute.

What does the encoding

The same H.264 encoder your machine uses for everything else, reached through the browser's WebCodecs interface. On most computers that is a dedicated block on the graphics chip, so the work is not being done in JavaScript and the speed does not depend on how fast this page's code is.

That makes it quick. A 20 second 720p clip came out in 2.6 seconds on the machine this was tested on, and a 6 second one in under a second, which is around seven times faster than watching it. A slower machine without a hardware encoder will be slower, and the progress bar gives a time remaining once it has something to base one on.

The piece a browser does not provide is the container. WebCodecs hands back a stream of encoded chunks with nothing wrapped around them, and a player needs those inside an MP4 with an index. That part is done by mediabunny, which is about 700 KB. The usual way to encode video in a web page is ffmpeg compiled to WebAssembly, whose core file alone is 64.7 MB, which is larger than a single file may be on the hosting this site runs on.

Nothing is uploaded. The file is read, decoded, encoded and written inside the tab, and the download at the end was made on your own machine. That is worth knowing before putting anything private into a site that offers to compress it.

Limits

500 MB per file.
The result is an MP4 with H.264 video, which is the combination that plays everywhere.
A file this browser cannot decode cannot be compressed. HEVC and ProRes are the usual refusals.
The whole output is held in memory while it is written, so a long 4K clip needs a machine with room for it.
The size figure is an estimate. A target in megabytes is held closely, within about one percent in testing, because the rate is fixed to hit it. A quality setting lets the encoder vary, and on deliberately difficult test footage it came out 17 percent over the estimate.

Frequently asked questions

How much smaller will my video get?: The estimate under the button says, and it updates as you change the settings. A phone records 1080p at around 17 Mbps and the balanced setting asks for 5.5, so footage straight off a phone usually lands near a third of its original size.
Will compressing it twice make it worse?: Yes. Each encode discards detail the next one cannot recover, so compressing an already compressed copy loses a second layer. Going back to the original and compressing once is always better than compressing the compressed version again.
Is my video uploaded anywhere?: No. It is decoded and re-encoded by your own browser and never leaves the machine. There is no server in this, which is also why the speed depends on your computer rather than on how busy a website is.
Why does the sound say it is being copied?: Because that is the default, and it is the better choice. The audio in a video has already been through an encoder once, and putting it through a second one for no reason loses a little more of it. Pick a bitrate instead if the sound itself needs to be smaller.
Can I compress a video on my phone?: Yes, if the browser is a recent Chrome or Safari, and a short clip is the sensible thing to try first. Phones have the same hardware encoders, though a long 4K video will warm the device up and may run out of memory before it finishes.