在这里给AVPlayer播放在线音频文件作个记号
1.在H文件中初始：
==============
AVPlayer *mp3Player;
AVPlayerItem *mp3PlayerItem;
id audioMix;
id volumeMixInput;


2.在MM文件中：
//作品播放
    NSURL * songUrl = [NSURL URLWithString:userInfo.songUrl];
    AVURLAsset *movieAsset    = [[[AVURLAsset alloc]initWithURL:songUrl options:nil]autorelease];

     self. mp3PlayerItem = [AVPlayerItem playerItemWithAsset:movieAsset];
     [self. mp3PlayerItem addObserver:self forKeyPath:@"status" options:0 context:NULL];
      self. mp3Player = [AVPlayer playerWithPlayerItem:self. mp3PlayerItem];
      AVPlayerLayer *playerLayer = [AVPlayerLayer playerLayerWithPlayer:self. mp3Player];
      playerLayer.frame = self.view.layer.bounds;
      playerLayer.videoGravity = AVLayerVideoGravityResizeAspect;
      [self.view.layer addSublayer:playerLayer];
       [self. mp3Player setAllowsExternalPlayback:YES];
    
3.实现代理方法：
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    if ([keyPath isEqualToString:@"status"])
    {
        if (AVPlayerItemStatusReadyToPlay == self. mp3Player.currentItem.status)
        {
            [self. mp3Player play];
        }
    }
}

4.现实音量调整
-(void) setVolume:(float)volume{
    //作品音量控制
    NSMutableArray *allAudioParams = [NSMutableArray array];
    AVMutableAudioMixInputParameters *audioInputParams =[AVMutableAudioMixInputParameters audioMixInputParameters];
    [audioInputParams setVolume:volume atTime:kCMTimeZero];
    [audioInputParams setTrackID:1];
    [allAudioParams addObject:audioInputParams];
    audioMix = [AVMutableAudioMix audioMix];
    [audioMix setInputParameters:allAudioParams];
    [self. mp3PlayerItem setAudioMix:audioMix]; // Mute the player item
    
    [avAudioPlayer setVolume:volume];
}

5.取得播放时间
- (NSTimeInterval) playableDuration
{
    AVPlayerItem * item = self.worksPlayer.currentItem;
    if (item.status == AVPlayerItemStatusReadyToPlay) {
        return CMTimeGetSeconds(self.worksPlayer.currentItem.duration);
    }
    else
    {
        return(CMTimeGetSeconds(kCMTimeInvalid));
    }
}
- (NSTimeInterval) playableCurrentTime
{
    AVPlayerItem * item = self.worksPlayer.currentItem;
    
    if (item.status == AVPlayerItemStatusReadyToPlay) {
        NSLog(@"%f\n",CMTimeGetSeconds(self.worksPlayer.currentItem.currentTime));
        if (!playBeginState&&CMTimeGetSeconds(self.worksPlayer.currentItem.currentTime)==CMTimeGetSeconds(self.worksPlayer.currentItem.duration)) {
            [streamer stop];
        }
        playBeginState = NO;
        return CMTimeGetSeconds(self.worksPlayer.currentItem.currentTime);
    }
    else
    {
        return(CMTimeGetSeconds(kCMTimeInvalid));
    }
}