If reason==MPV_END_FILE_REASON_ERROR, this contains a mpv error code
(one of MPV_ERROR_...) giving an approximate reason why playback
failed. In other cases, this field is 0 (no error).
Since API version 1.9.
Playlist entry ID of the file that was being played or attempted to be
played. This has the same value as the playlist_entry_id field in the
corresponding mpv_event_start_file event.
Since API version 1.108.
If loading ended, because the playlist entry to be played was for example
a playlist, and the current playlist entry is replaced with a number of
other entries. This may happen at least with MPV_END_FILE_REASON_REDIRECT
(other event types may use this for similar but different purposes in the
future). In this case, playlist_insert_id will be set to the playlist
entry ID of the first inserted entry, and playlist_insert_num_entries to
the total number of inserted playlist entries. Note this in this specific
case, the ID of the last inserted entry is playlist_insert_id+num-1.
Beware that depending on circumstances, you may observe the new playlist
entries before seeing the event (e.g. reading the "playlist" property or
getting a property change notification before receiving the event).
Since API version 1.108.