Rotation Lock is a useful feature that I use on my iPhone almost every single day. People use Rotation Lock for a bevy of different reasons, but many would coin video consumption to be a valid use since it can prevent the display from rotating to an uncomfortable orientation in those niche moments like laying in your bed.
Currently, the fastest and most convenient way to toggle Rotation Lock is via the dedicated Control Center toggle, but launching Control Center can interrupt your video playback. With that in mind, wouldn’t it have made perfect sense if Apple had simply integrated a Rotation Lock button into the video player interface to begin with?