HTML5 is default in Sierra/Safari 10, Harv.

Originally Posted By: Apple
Picture in Picture in macOS
Safari 10 brings Picture in Picture to macOS so users can watch video in a separate, resizable window that stays on top of other application windows and remains on-screen when switching desktop spaces.
Safari's default HTML5 video controls includes a new Picture in Picture control.
If you use custom HTML5 video controls, you can add Picture in Picture functionality using the JavaScript presentation mode API. (Emphasis added)

More: Safari 10 will prefer HTML5

(The downside is this pop-up, which pops up with infuriating regularity.

Last edited by artie505; 05/06/17 06:41 PM. Reason: Add link
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In Memory of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire