Abbreviation for "Picture in Picture Open Source Software"
Brings Picture in Picture shortcut and custom button to any video.
Via Homebrew Cask (Recommended)
brew install --cask --no-quarantine artginzburg/tap/pipossCheck out the cask if you're interested.
Run the app, enable the PiPOSS extension in Safari, and give it access if it requests anything.
Now you'll be able to use P on your keyboard to toggle Picture in Picture mode for currently playing or the first appearing video on the page.
Also, YouTube will have a button for Picture in Picture.
If macOS refuses to run the app, run it via Ctrl+Click > Open.