Shows, how many seconds of the media were actually played, accumulated across all views of the media.
User A watches a video for 30 seconds, rewinds it, and watches another 20 seconds. The Play Duration for User A is 50 seconds, regardless of to which point the video was rewound.
User B watches a video for 10 seconds. The Play Duration for USer B is 10 seconds.
In total, the Play duration is 60 seconds, if no other user watched the video in the chosen time frame.