Video Size Target Compressor

About Video Size Target Compressor

Many upload forms and platforms cap file size at a hard limit — a 25MB email attachment, a 100MB submission portal — and knowing what quality setting will actually land you under that limit is mostly guesswork with a generic compressor. This tool works backward from your target size instead: tell it the size you need, and it calculates the exact bitrate required.

The math is straightforward but precise: your target size in megabytes converts to a total bit budget, the video's actual duration (read automatically from the uploaded file) determines how that budget spreads across the timeline, and a fixed audio bitrate (128kbps) is subtracted first so the remaining budget goes entirely toward video quality at the calculated bitrate.

A real FFmpeg build compiled to WebAssembly runs the compression entirely inside your browser using this calculated bitrate, encoding with the fast "veryfast" preset since single-pass bitrate-targeted encoding doesn't need the extra encoding passes a maximum-efficiency encode would use.

Because this uses single-pass encoding (rather than a slower two-pass approach that can hit an exact target more precisely), the actual result typically lands close to your target size but not always exactly at it — variance depends on how much the video's content complexity varies over its length. The exact resulting size is shown after compression so you know precisely where it landed.

How it works

1. Upload your video. Duration is detected automatically.
2. Set your target size in MB. The required bitrate is calculated from size and duration.
3. Compress and download. See the exact resulting size once it's done.