从AVPlayer获取HLS的PCM数据

Question

这个问题在过去几年里似乎被问了几次，但都没有答案。我正在尝试处理来自HLS的PCM数据，我必须使用AVPlayer。

这篇文章点击了本地文件https://chritto.wordpress.com/2013/01/07/processing-avplayers-audio-with-mtaudioprocessingtap/

此水龙头适用于远程文件，但不适用于. m3u8 hls文件。http://venodesigns.net/2014/01/08/recording-live-audio-streams-on-ios/

我可以播放播放列表中的前两首曲目，但它不会启动获取pcm所需的回调，当文件是本地或远程（不是流）时，我仍然可以获取pcm，但它是hls不工作，我需要HLS工作

这是我的代码

//avplayer tap try
- (void)viewDidLoad {
    [super viewDidLoad];

    NSURL*testUrl= [NSURL URLWithString:@"http://playlists.ihrhls.com/c5/1469/playlist.m3u8"];

    AVPlayerItem *item = [AVPlayerItem playerItemWithURL:testUrl];
    self.player = [AVPlayer playerWithPlayerItem:item];

    // Watch the status property - when this is good to go, we can access the
    // underlying AVAssetTrack we need.
    [item addObserver:self forKeyPath:@"status" options:0 context:nil];

}

-(void)observeValueForKeyPath:(NSString *)keyPath
ofObject:(id)object
change:(NSDictionary *)change
context:(void *)context
{
    if(![keyPath isEqualToString:@"status"])
        return;

    AVPlayerItem *item = (AVPlayerItem *)object;
    if(item.status != AVPlayerItemStatusReadyToPlay)
        return;

    NSArray *tracks = [self.player.currentItem tracks];
    for(AVPlayerItemTrack *track in tracks) {
        if([track.assetTrack.mediaType isEqualToString:AVMediaTypeAudio]) {
            NSLog(@"GOT DAT FUCKER");
            [self beginRecordingAudioFromTrack:track.assetTrack];
            [self.player play];
        }
    }
}

- (void)beginRecordingAudioFromTrack:(AVAssetTrack *)audioTrack
{
    // Configure an MTAudioProcessingTap to handle things.
    MTAudioProcessingTapRef tap;
    MTAudioProcessingTapCallbacks callbacks;
    callbacks.version = kMTAudioProcessingTapCallbacksVersion_0;
    callbacks.clientInfo = (__bridge void *)(self);
    callbacks.init = init;
    callbacks.prepare = prepare;
    callbacks.process = process;
    callbacks.unprepare = unprepare;
    callbacks.finalize = finalize;

    OSStatus err = MTAudioProcessingTapCreate(
                                              kCFAllocatorDefault,
                                              &callbacks,
                                              kMTAudioProcessingTapCreationFlag_PostEffects,
                                              &tap
                                              );

    if(err) {
        NSLog(@"Unable to create the Audio Processing Tap %d", (int)err);
        return;
    }

    // Create an AudioMix and assign it to our currently playing "item", which
    // is just the stream itself.
    AVMutableAudioMix *audioMix = [AVMutableAudioMix audioMix];
    AVMutableAudioMixInputParameters *inputParams = [AVMutableAudioMixInputParameters
                                                     audioMixInputParametersWithTrack:audioTrack];

    inputParams.audioTapProcessor = tap;
    audioMix.inputParameters = @[inputParams];
    self.player.currentItem.audioMix = audioMix;
}

void process(MTAudioProcessingTapRef tap, CMItemCount numberFrames,
             MTAudioProcessingTapFlags flags, AudioBufferList *bufferListInOut,
             CMItemCount *numberFramesOut, MTAudioProcessingTapFlags *flagsOut)
{
    OSStatus err = MTAudioProcessingTapGetSourceAudio(tap, numberFrames, bufferListInOut,
                                                      flagsOut, NULL, numberFramesOut);
    if (err) NSLog(@"Error from GetSourceAudio: %d", (int)err);

    NSLog(@"Process");

}

void init(MTAudioProcessingTapRef tap, void *clientInfo, void **tapStorageOut)
{
    NSLog(@"Initialising the Audio Tap Processor");
    *tapStorageOut = clientInfo;
}

void finalize(MTAudioProcessingTapRef tap)
{
    NSLog(@"Finalizing the Audio Tap Processor");
}

void prepare(MTAudioProcessingTapRef tap, CMItemCount maxFrames, const AudioStreamBasicDescription *processingFormat)
{
    NSLog(@"Preparing the Audio Tap Processor");
}

void unprepare(MTAudioProcessingTapRef tap)
{
    NSLog(@"Unpreparing the Audio Tap Processor");
}

void init被称为void prepare，也必须调用process。

我该怎么做？

Answer 1

我建议使用奴佛卡因

在iOS和Mac OS X中，使用音频单元实现真正快速的音频是很困难的，这会让你伤痕累累、血肉模糊。过去需要几天的时间，现在只需几行代码就可以完成。

Answer 2

我建议您使用FFMPEG库来处理HLS流。这有点难，但提供了更多的灵活性。几年前，我为Android制作了HLS Player（使用了这个项目），我相信这同样适用于iOS。