The meaning and contents of the data member depend on the event_id:
MPV_EVENT_GET_PROPERTY_REPLY: mpv_event_property*
MPV_EVENT_PROPERTY_CHANGE: mpv_event_property*
MPV_EVENT_LOG_MESSAGE: mpv_event_log_message*
MPV_EVENT_CLIENT_MESSAGE: mpv_event_client_message*
MPV_EVENT_START_FILE: mpv_event_start_file* (since v1.108)
MPV_EVENT_END_FILE: mpv_event_end_file*
MPV_EVENT_HOOK: mpv_event_hook*
MPV_EVENT_COMMAND_REPLY* mpv_event_command*
other: NULL
This is mainly used for events that are replies to (asynchronous)
requests. It contains a status code, which is >= 0 on success, or < 0
on error (a mpv_error value). Usually, this will be set if an
asynchronous request fails.
Used for:
MPV_EVENT_GET_PROPERTY_REPLY
MPV_EVENT_SET_PROPERTY_REPLY
MPV_EVENT_COMMAND_REPLY
If the event is in reply to a request (made with this API and this
API handle), this is set to the reply_userdata parameter of the request
call. Otherwise, this field is 0.
Used for:
MPV_EVENT_GET_PROPERTY_REPLY
MPV_EVENT_SET_PROPERTY_REPLY
MPV_EVENT_COMMAND_REPLY
MPV_EVENT_PROPERTY_CHANGE
MPV_EVENT_HOOK