A long time ago (in Internet time) that actually was the case. HTML, the code which makes webpages, natively supports embedding all sorts of media, as long as the computer loading the page can play it (in the past, it would use apps like Windows Media Player and QuickTime to handle the computer side of things).
This worked okay, but didn’t protect videos so anyone could download any video. You can imagine that Disney wouldn’t want you to be able to download videos from their site. It also meant slower video loading. Now sites like YouTube store different quality of video and pick the quickest loading version (lower quality means smaller file) but also put the video in a custom player that they can restrict the ability to download it and put ads in.
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