A minute of phone video is easily a hundred megabytes or more — far over most email attachment limits, and slow to send on a messaging app. Re-encoding it at a sensible quality makes it a fraction of the size.
Pick the trade-off
There are four levels: Visually Lossless, High Quality, Web Standard (the default) and Small File. Web Standard suits sharing online; pick Small File when you must fit a strict size limit, and Visually Lossless when you want to keep quality for editing.
What you get
The video is re-encoded to H.264 with AAC audio and saved as an MP4, which plays on virtually every phone, computer and messaging app, and starts playing before it has fully downloaded.
It runs on your device
Encoding uses ffmpeg compiled to WebAssembly, inside the page, so the video is not uploaded. Free use covers videos up to 5 minutes; long or 4K videos take a while in the browser, so leave the tab open until the progress bar finishes.
Only need part of it?
Trimming the clip to the moment that matters is the biggest saving of all — do that first, then compress.