// listening for current item change
self.audioQueueObserver = self.playerQueue?.observe(\.currentItem, options: [.new]) {
    [weak self] (player, _) in
    print("media item changed...")
}

// listening for current item status change
self.audioQueueStatusObserver = self.playerQueue?.currentItem?.observe(\.status, options:  [.new, .old], changeHandler: {
    (playerItem, change) in
    if playerItem.status == .readyToPlay {
        print("current item status is ready")
    }
})

// listening for buffer is empty
self.audioQueueBufferEmptyObserver = self.playerQueue?.currentItem?.observe(\.playbackBufferEmpty, options: [.new]) {
    [weak self] (_, _) in
    print("buffering...")
}
// listening for event that buffer is almost full
self.audioQueueBufferAlmostThereObserver = self.playerQueue?.currentItem?.observe(\.playbackLikelyToKeepUp, options: [.new]) {
    [weak self] (_, _) in
    print("buffering ends...")
}

// listening for event that buffer is full
self.audioQueueBufferFullObserver = self.playerQueue?.currentItem?.observe(\.playbackBufferFull, options: [.new]) {
    [weak self] (_, _) in
    print("buffering is hidden...")
}

// listening for event about the status of the playback
self.audioQueueStallObserver = self.playerQueue?.observe(\.timeControlStatus, options: [.new, .old], changeHandler: {
    (playerItem, change) in
    if #available(iOS 10.0, *) {
        switch (playerItem.timeControlStatus) {
            case AVPlayerTimeControlStatus.paused:
            print("Media Paused")
            case AVPlayerTimeControlStatus.playing:
            print("Media Playing")
            case AVPlayerTimeControlStatus.waitingToPlayAtSpecifiedRate:
            print("Media Waiting to play at specific rate!")
        }
    }
    else {
        // Fallback on earlier versions
    }
})

// listening for change event when player stops playback
self.audioQueueWaitingObserver = self.playerQueue?.observe(\.reasonForWaitingToPlay, options: [.new, .old], changeHandler: {
    (playerItem, change) in
    if #available(iOS 10.0, *) {
        print("REASON FOR WAITING TO PLAY: ", playerItem.reasonForWaitingToPlay?.rawValue as Any)
    }
    else {
        // Fallback on earlier versions
    }
})