在iOS上播放一定时间的循环音频

Question

我想知道在iOS上循环播放音频的最佳解决方案是什么。我现在在玩

• AVAudioPlayer (在这里，我可以定义重复计数，但不能定义结束时间)
• AVPlayer (在这里，我可以定义一个forwardPlaybackEndTime机器人，而不是循环计数)
• AVPlayerLooper (我还没有完全理解)

所以我需要的是定义一个特定声音文件被重复的持续时间。F.e.我有一个8秒的mp3，我想播放它一分钟。

如果我能在它重新开始的时候褪色的话，那就更好了。

Answer 1

你和AVPlayerLooper走在正确的轨道上。

这是如何设置AVPlayerLooper的

var playerLooper: AVPlayerLooper!
var player: AVQueuePlayer!

func play(_ url: URL) {
    let asset = AVAsset(url: url)
    let playerItem = AVPlayerItem(asset: asset)

    player = AVQueuePlayer(playerItem: playerItem)
    playerLooper = AVPlayerLooper(player: player, templateItem: playerItem)

    player.play()
}

要在设定的时间后停止循环，可以使用addBoundaryTimeObserver(forTimes:queue:using:)，例如：

let assetDuration = CMTimeGetSeconds(asset.duration)
let maxDuration = 60.0 // Define max duration
let maxLoops = floor(maxDuration / assetDuration)
let lastLoopDuration = maxDuration - (assetDuration * maxLoops)
let boundaryTime = CMTimeMakeWithSeconds(lastLoopDuration, preferredTimescale: 1)
let boundaryTimeValue = NSValue(time: boundaryTime)

player.addBoundaryTimeObserver(forTimes: [boundaryTimeValue], queue: DispatchQueue.main) { [weak self] in
    if self?.playerLooper.loopCount == Int(maxLoops) {
        self?.player.pause()
    }
}

为了渐入/退出，您必须在使用audioMix之前将它设置为您的AVPlayerItem实例。

let introRange = CMTimeRangeMake(start: CMTimeMakeWithSeconds(0, preferredTimescale: 1), duration: CMTimeMakeWithSeconds(1, preferredTimescale: 1))
let endingSecond = CMTimeRangeMake(start: CMTimeMakeWithSeconds(assetDuration - 1, preferredTimescale: 1), duration: CMTimeMakeWithSeconds(1, preferredTimescale: 1))

let inputParams = AVMutableAudioMixInputParameters(track: asset.tracks.first! as AVAssetTrack)
inputParams.setVolumeRamp(fromStartVolume: 0, toEndVolume: 1, timeRange: introRange)
inputParams.setVolumeRamp(fromStartVolume: 1, toEndVolume: 0, timeRange: endingSecond)

let audioMix = AVMutableAudioMix()
audioMix.inputParameters = [inputParams]
playerItem.audioMix = audioMix

功能齐全：

func play(_ url: URL) {
    let asset = AVAsset(url: url)
    let playerItem = AVPlayerItem(asset: asset)

    let assetDuration = CMTimeGetSeconds(asset.duration)

    let introRange = CMTimeRangeMake(start: CMTimeMakeWithSeconds(0, preferredTimescale: 1), duration: CMTimeMakeWithSeconds(1, preferredTimescale: 1))
    let endingSecond = CMTimeRangeMake(start: CMTimeMakeWithSeconds(assetDuration - 1, preferredTimescale: 1), duration: CMTimeMakeWithSeconds(1, preferredTimescale: 1))

    let inputParams = AVMutableAudioMixInputParameters(track: asset.tracks.first! as AVAssetTrack)
    inputParams.setVolumeRamp(fromStartVolume: 0, toEndVolume: 1, timeRange: introRange)
    inputParams.setVolumeRamp(fromStartVolume: 1, toEndVolume: 0, timeRange: endingSecond)

    let audioMix = AVMutableAudioMix()
    audioMix.inputParameters = [inputParams]
    playerItem.audioMix = audioMix

    player = AVQueuePlayer(playerItem: playerItem)
    playerLooper = AVPlayerLooper(player: player, templateItem: playerItem)
    player.play()

    let maxDuration = 60.0 // Define max duration
    let maxLoops = floor(maxDuration / assetDuration)
    let lastLoopDuration = maxDuration - (assetDuration * maxLoops)
    let boundaryTime = CMTimeMakeWithSeconds(lastLoopDuration, preferredTimescale: 1)
    let boundaryTimeValue = NSValue(time: boundaryTime)

    player.addBoundaryTimeObserver(forTimes: [boundaryTimeValue], queue: DispatchQueue.main) { [weak self] in
        if self?.playerLooper.loopCount == Int(maxLoops) {
            self?.player.pause()
        }
    }
}