Compress an MP4 by saying how small it should be

What the plan shows before anything runs

An MP4's size comes mostly from its video bitrate multiplied by its length. ToolGPT reads both from your file and picks a target bitrate below the current one. The plan then shows the expected size as a range rather than one exact number, because an encoder lands near its target, not exactly on it.

By default the output keeps the original resolution and frame rate. For a large reduction, the assistant may suggest a smaller resolution, such as 1080p from a 4K source, because a smaller picture needs fewer bits to look sharp. If you disagree with a setting, say so and you get a revised plan.

It stays an MP4

The compressed file is an MP4 with H.264 video and AAC audio, a combination that plays on nearly every phone, computer and website. If you want another container, ask for WEBM, MOV or MKV in the same message.

ToolGPT uses your browser's built-in video encoder when it can, which is fast because it can use the graphics hardware. When the browser cannot encode what is needed, a WebAssembly build of FFmpeg does the work instead, at no more than 30 frames per second. Either way, the compression runs in your browser.

When an MP4 is already as small as it gets

Many MP4 files are already compressed efficiently, especially ones saved from streaming sites. If the planned settings would not make the file at least 5% smaller, ToolGPT does not run the job. It tells you the file is already efficiently compressed and suggests what could still work: a much lower bitrate or a smaller resolution. If a finished file still comes out no smaller than the original, it is discarded instead of being handed to you.