With macOS (Sierra and higher), Apple has provided a convenient — and fun — Picture in Picture (PiP) feature. You can “float” a video window from Safari or iTunes/Apple TV over your desktop or a full-screen app. You can see my article on how to use it here. However, with the introduction of Safari 13, Apple has kicked things up a notch.
When you’re watching a video in the Safari web browser, you now make it “jump off” the webpage into a separate window of its own. Go to the page displaying the video, then click and hold the Volume icon in the navigation bar. A menu will pop up. Select Enter Picture in Picture and the video appears in its own window. You can resize and/or snap it to an edge of the screen.
To exit PiP, click on the close window icon (the X button) in the upper left corner of the video pop-up window. Alternately, you can click and hold on the Audio icon in the URL box and select Exit Picture in Picture.
Apple has also added support for PiP to QuickTime Player. You can play video in a resizable window that isn’t blocked by other windows.
To do this launch QuickTime Player. Use the playback controls to play the video file. Click the picture-in-picture button in the playback controls. You can click and drag the picture-in-picture window to anywhere on the screen, or click and drag any edge of the window to resize it. Click the full-screen button or the close button to close the picture-in-picture window.