How this WhatsApp video compressor works
This compressor re-encodes a video so it aims under 16 MB, the size WhatsApp sends as media. A file above that is harder to send as a normal video in a chat. The result is an MP4 with H.264 video and AAC sound that plays on almost every phone.
VimCut works out a bitrate from the length of the clip, so a short clip keeps more detail and a longer one gets less. When the budget is tight the picture is scaled down so the file still fits. Sound is set to 64 kbps. If your file is already under 16 MB, it is returned unchanged and nothing is encoded. When your browser supports it, the work uses the built-in hardware encoder. Otherwise it falls back to WebAssembly (ffmpeg.wasm). The result is a normal MP4 that you download and send in WhatsApp yourself.