使用 AVAudioTime 安排将来播放的音频文件

Question

我正在尝试弄清楚如何在不久的将来正确安排音频文件。我的实际目标是同步播放多首曲目。

那么如何正确配置 'aTime' 使其在大约 0.3 秒后启动。我想我可能也需要 hostTime，但我不知道如何正确使用它

func createStartTime() -> AVAudioTime? {
    var time:AVAudioTime?
    if let lastPlayer = self.trackPlayerDictionary[lastPlayerKey] {
        if let sampleRate = lastPlayer.file?.processingFormat.sampleRate {
            var sampleTime = AVAudioFramePosition(shortStartDelay * sampleRate )
            time = AVAudioTime(sampleTime: sampleTime, atRate: sampleRate)
        }
    }
    return time
}

这是我用来开始播放的函数：

func playAtTime(aTime:AVAudioTime?){
    self.startingFrame = AVAudioFramePosition(self.currentTime * self.file!.processingFormat.sampleRate)
    let frameCount = AVAudioFrameCount(self.file!.length - self.startingFrame!)

    self.player.scheduleSegment(self.file!, startingFrame: self.startingFrame!, frameCount: frameCount, atTime: aTime, completionHandler:{ () -> Void in
        NSLog("done playing")//actually done scheduling
    })
    self.player.play()

}

Answer 1

我想通了！

我在mach_absolute_time()中填写的hostTime参数，这是computer/iPad的'now'时间。 AVAudioTime(hostTime:sampleTime:atRate) 将 sampleTime 添加到 hostTime 并在不久的将来返回一个时间，可用于在同一 startingTime

安排多个音频段

func createStartTime() -> AVAudioTime? {

    var time:AVAudioTime?
    if let lastPlayer = self.trackPlayerDictionary[lastPlayerKey] {

        if let sampleRate = lastPlayer.file?.processingFormat.sampleRate {

            var sampleTime = AVAudioFramePosition(shortStartDelay * sampleRate )

            time = AVAudioTime(hostTime: mach_absolute_time(), sampleTime: sampleTime, atRate: sampleRate)
        }
    }
    return time

}

Answer 2

好吧 - 它是 ObjC - 但你会明白重点的...

不需要 mach_absolute_time() - 如果你的引擎是运行ning 你已经有一个 @属性 AVAudioNode 中的 lastRenderTime - 你的播放器的 superclass ...

AVAudioFormat *outputFormat = [playerA outputFormatForBus:0];

const float kStartDelayTime = 0.0; // seconds - in case you wanna delay the start

AVAudioFramePosition startSampleTime = playerA.lastRenderTime.sampleTime;

AVAudioTime *startTime = [AVAudioTime timeWithSampleTime:(startSampleTime + (kStartDelayTime * outputFormat.sampleRate)) atRate:outputFormat.sampleRate];

[playerA playAtTime: startTime];
[playerB playAtTime: startTime];
[playerC playAtTime: startTime];
[playerD playAtTime: startTime];

[player...

顺便说一句 - 您可以使用 AVAudioPlayer 获得相同的 100% 采样帧准确结果 class...

NSTimeInterval startDelayTime = 0.0; // seconds - in case you wanna delay the start
NSTimeInterval now = playerA.deviceCurrentTime;

NSTimeInterval startTime = now + startDelayTime;

[playerA playAtTime: startTime];
[playerB playAtTime: startTime];
[playerC playAtTime: startTime];
[playerD playAtTime: startTime];

[player...

在没有 startDelayTime 的情况下，所有玩家的前 100-200 毫秒将被截断，因为尽管玩家已经开始（嗯，已安排），但开始命令实际上将其时间用于运行循环 100% 现在同步。但是有了 startDelayTime = 0.25 你就可以开始了。永远不要忘记提前 prepareToPlay 你的玩家，这样在开始时就不需要做额外的缓冲或设置 - 只是让他们开始 ;-)

如需更深入的解释，请查看我在

中的回答

AVAudioEngine multiple AVAudioInputNodes do not play in perfect sync

使用 AVAudioTime 安排将来播放的音频文件

Scheduling an audio file for playback in the future with AVAudioTime

objective-c

core-audio

ios

swift