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.
Corresponds to the values in enum mpv_end_file_reason (the "int" type will be replaced with mpv_end_file_reason on the next ABI bump).