在 iOS 安排音频样本播放

Question

在 iOS 应用程序 (Swift) 中，我如何安排音频样本在准确的时间播放？

我想通过安排音频样本在准确的时间播放来制作音乐 - 一系列“曲目”。我有一些想法，我应该使用 AVFoundation，但我发现缺乏服务于这个特定用例的文档。

我知道 AudioKit 存在，但我希望最终将我的应用程序移动到 Apple Watch，目前 AudioKit 不支持它。

Answer 1

我想出了我需要做的事情。

创建一个 AVMutableComposition，添加一个可变轨道，并在该轨道上添加片段（静音和声音资产视图）

import AVFoundation

let drumUrl = Bundle.main.url(forResource: "bd_909dwsd", withExtension: "wav")!

func makePlayer(bpm: Float, beatCount: Int) -> AVPlayer? {
    let beatDuration = CMTime(seconds: Double(60 / bpm), preferredTimescale: .max)
    
    let composition = AVMutableComposition()
    guard let track = composition.addMutableTrack(withMediaType: .audio, preferredTrackID: kCMPersistentTrackID_Invalid) else {
        return nil
    }
    
    let drumAsset = AVAsset(url: drumUrl)
    let drumDuration = drumAsset.duration
    let drumTimeRange = CMTimeRange(start: CMTime.zero, duration: drumDuration)
    
    let silenceDuration = beatDuration - drumDuration
    
    var prevBeatEnd = CMTime.zero
    
    for deatIndex in 0 ..< beatCount {
        let drumTargetRange = CMTimeRange(start: prevBeatEnd, duration: drumDuration)
        let drumSegment = AVCompositionTrackSegment(url: drumUrl, trackID: track.trackID, sourceTimeRange: drumTimeRange, targetTimeRange: drumTargetRange)
        track.segments.append(drumSegment)
        
        if deatIndex == 0 {
            prevBeatEnd = prevBeatEnd + drumDuration
        } else {
            let silenceTargetRange = CMTimeRange(start: prevBeatEnd, duration: silenceDuration)
            track.insertEmptyTimeRange(silenceTargetRange)
            prevBeatEnd = prevBeatEnd + silenceDuration + drumDuration
        }
    }
    
    try! track.validateSegments(track.segments)
    
    let playerItem = AVPlayerItem(asset: composition)
    
    return AVPlayer(playerItem: playerItem)
}

在 iOS 安排音频样本播放

Scheduling Audio Sample Playback on iOS

scheduling

sample

avfoundation

sequencing