Optional issuerThe issuer of this event, as passed into the according API method. 'api' by default if no issuer was specified.
Previous audio track or null if no audio track was enabled before.
New audio track.
Current playback time in seconds.
The timestamp (in milliseconds) when this event was fired.
Event type.
Events which can be triggered by user interaction as well as internally.
The issuer is to determine whether this was triggered internally ('api') or by the UI ('ui')