Shrink a video to fit under a limit

Size, in bytes, at eight bits to the byte, spread across the clip's own length, gives a bits-per-second budget — the bitrate that clip needs to land under the target. Kept audio is subtracted from that budget first, using its own measured bitrate, because audio you keep still counts against the limit you asked for. A 10% margin comes off what's left before the encoder ever sees it, since a variable-bitrate encoder produces an average over the whole clip, not a hard ceiling on every frame.

Spread a very small bitrate budget across a lot of pixels and every one of them is starved — that's the blocky, smeared look people mean by “compressed to death”. Past a certain point it's the picture size, not the encoder, losing the fight. So in size-target mode this checks how much of the budget each pixel would actually get and steps the long side down — 1080, then 720, then 480, then 360 — only as far as it needs to, stopping the moment a resolution has enough room. Quality mode never touches the picture size at all.

The bitrate calculation is a plan, not a guarantee — encoders vary. The real file size is measured after encoding, and if one unlucky pass still lands over the target, this tool automatically tries again once at a lower bitrate. If it's still over after that, the summary says so plainly rather than handing over a file that misses the limit.

Decoding, the bitrate math and the video encoding all happen in this page. There is no server here to send the video to, and the page's security policy blocks any connection to anywhere but this site. Here is how that is enforced.