Optionaldelegate: PlayerDomControllerElement sidecar videos without own host element are mounted into, layered over main media.
Binds element to controller, controller events are dispatched as media element events
Optionaloptions: VideoKeyframeOptionsDispatches media element events for state that is resolved on wiring, ie. duration
StaticmountMounts virtual playback element in place of delegate's video element. Video element is hidden until destroyed.
Element is inserted before video element and takes its slot, so media-chrome's media-controller (which uses first element in media slot) observes it as media.
VirtualPlaybackDomController that renders black slate with current timecode.