Optional issuerThe issuer of this event, as passed into the according API method. 'api' by default if no issuer was specified.
Current playback time (in seconds)
The time at which this event was fired
The affected audio track
Event type, e.g. 'play'
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')