AVPlayer实时流如何获得功率以进行音频电平计量 [英] AVPlayer Live stream how to get power for audio level metering

问题描述

我试图在我的应用中显示一个仪表图，该仪表图使用AVPlayer传输实时音频流.

I am trying to show a meter graph in my app which uses AVPlayer to stream live audio streams.

我知道对于AVAudioPlayer，有一种方法如下: 试图了解AVAudioPlayer和音频电平计量

I know for AVAudioPlayer there is a way as per: Trying to understand AVAudioPlayer and audio level metering

使用peakPowerForChannel

但是AVAudioPlayer不适用于音频流.

But AVAudioPlayer doesn't work for audio streams.

AVPlayer是否有类似的东西?还是有其他方法可以从AVPlayer获取功率值?

Is there something similar for AVPlayer? Or is there any other way I can get the power values from the AVPlayer?

代码:

[[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryPlayback error:nil];
    if (self.avplayer) {
        [self.avplayer replaceCurrentItemWithPlayerItem:nil];
    }
    AVURLAsset *avAsset = [[AVURLAsset alloc] initWithURL:[NSURL URLWithString:@"http://broadcast.infomaniak.net/radionova-high.mp3"] options:nil];
    NSArray *keys = @[@"playable"];
    [avAsset loadValuesAsynchronouslyForKeys:keys completionHandler:^{
        dispatch_async(dispatch_get_main_queue(), ^{
            AVPlayerItem *newItem = [[AVPlayerItem alloc] initWithAsset:avAsset];
            if (!self.avplayer) {
                self.avplayer = [[AVPlayer alloc] initWithPlayerItem:newItem];
            } else {
                [self.avplayer replaceCurrentItemWithPlayerItem:newItem];
            }
            [self.avplayer addObserver:self forKeyPath:@"status" options:(NSKeyValueObservingOptionNew | NSKeyValueObservingOptionInitial) context:nil];
            [self.avplayer addObserver:self forKeyPath:@"rate" options:(NSKeyValueObservingOptionNew | NSKeyValueObservingOptionInitial) context:nil];
        });
    }];

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object
                        change:(NSDictionary *)change context:(void *)context {
    NSLog(@"%@ called",keyPath);
    if ( [keyPath isEqualToString:@"status"]) {
        [self.avplayer play];
    } else if ( [keyPath isEqualToString:@"rate"]) {
        if (self.avplayer.rate) {
            NSLog(@"Playing...");
            [[NSNotificationCenter defaultCenter] postNotificationName:@"currentPlayingChangedToPlay" object:nil];

        } else {
            NSLog(@"Not playing...");
            [[NSNotificationCenter defaultCenter] postNotificationName:@"currentPlayingChangedToPause" object:nil];
        }
    }

}

推荐答案

通常，您可以通过在播放器项目上使用MTAudioProcessingTap来获取AVPlayer的音频样本，但是您的资产会对此进行抵抗

Ordinarily, you can get at the audio samples of an AVPlayer by using an MTAudioProcessingTap on the player item, however your asset resists this through

1. AVURLAsset上的tracks属性从不可用
2. 当您观察并将水龙头连接到playerItem.tracks的assetTrack时，请不要回电.

1. the tracks property on your AVURLAsset never becoming available
2. not calling you back when you observe and attach the tap to your playerItem.tracks's assetTrack.

我从未见过很好的解释，为什么它不适用于远程mp3或m3u8流，但令人讨厌的是，它确实适用于其他远程资产类型，例如aac.不公平地，在视频方面， AVPlayerItemVideoOutput 似乎适用于所有类型的资产(除非存在DRM问题)！

I've never seen a good explanation for why this doesn't work for remote mp3s or m3u8 streams, and annoyingly, it does work for other remote asset types, like aac. Unjustly, on the video side, AVPlayerItemVideoOutput seems to work for all types of assets (barring DRM problems)!

那么这会让你离开哪里?一种方法是自己流式传输mp3数据，您可以在其中使用AudioQueue对其进行解码和播放，然后 使用上述MTAudioProcessingTap计算峰值功率.还想到了涉及AudioConverter/AudioUnit和AVAudioConverter/AVAudioEngine的解决方案.

So where does this leave you? One way is to stream the mp3 data yourself from where you can decode and play it using an AudioQueue, and also calculate the peak power using the aforementioned MTAudioProcessingTap. Solutions involving AudioConverter/AudioUnit and AVAudioConverter/AVAudioEngine come to mind too.

如果只是为了替换单个属性而听起来工作量太大，则可以查看预先烘焙的解决方案，例如 FreeStreamer ，然后计算功效.您可能会找到一个可以为您计算功率的库.如果没有，您可以使用此公式

If that sounds like too much work just to replace a single property, you could look at pre-baked solutions, like StreamingKit or FreeStreamer and then calculate power. You may find a library that calculates power for you. If not, you can calculate peakPowerForChannel using this formula

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