One of the major new features Apple introduced in iOS 9 was the ability to take advantage of Picture in Picture mode on supported iPad models; a multitasking mode perfect for watching videos while tackling other tasks at the same time, such as web browsing, document writing, social networking, and more.
Oddly enough, the Apple TV, which is essentially a media entertainment system in itself, doesn't come with a similar feature for users wanting to multitask more efficiently on their television sets.
Developer Steve Troughton-Smith has demonstrated Picture in Picture multitasking on the Apple TV 4 via a custom app he made for himself, showing that the hardware inside of the Apple TV on the latest firmware is capable of handing the feature, but it appears Apple has chosen not to include it (yet).