ios - scaleTimeRange 对音频类型 AVMutableCompositionTrack 没有影响

Question

我正在开发一款简单的视频编辑应用。我想在我的应用程序中添加慢动作。我注意到 AVMutableCompositionTrack 类中有一个 scaleTimeRange 方法，因此我使用它来实现我的目的。我发现 scaleTimeRange 在视频轨道上效果很好，但对音频轨道没有任何影响。这意味着音轨仍以原始速度播放。

下面是我的代码:

    CMTime insertionPoint = kCMTimeZero;

    double wholeDuration = CMTimeGetSeconds([asset duration]);
    double doubleDuration = CMTimeGetSeconds([asset duration])*2.0;
    CMTime trimmedDuration = CMTimeMakeWithSeconds(wholeDuration, 600.0);

    // Create a new composition
    self.mutableComposition = [AVMutableComposition composition];

    // Insert video and audio tracks from AVAsset
    if(assetVideoTrack != nil) {
        AVMutableCompositionTrack *compositionVideoTrack = [self.mutableComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
        [compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, trimmedDuration) ofTrack:assetVideoTrack atTime:insertionPoint error:&error];

        [compositionVideoTrack scaleTimeRange:CMTimeRangeMake(kCMTimeZero, trimmedDuration) toDuration:CMTimeMakeWithSeconds(doubleDuration, 600.0)];
    }
    if(assetAudioTrack != nil) {
        AVMutableCompositionTrack *compositionAudioTrack = [self.mutableComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
        [compositionAudioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, trimmedDuration) ofTrack:assetAudioTrack atTime:insertionPoint error:&error];

        [compositionAudioTrack scaleTimeRange:CMTimeRangeMake(kCMTimeZero, trimmedDuration) toDuration:CMTimeMakeWithSeconds(doubleDuration, 600.0)];
    }

谁能给我一些关于这个问题的建议？谢谢!

Answer 1

为了能够播放带有声音的慢动作，只需为 AVPlayerItem 设置适当的 audioTimePitchAlgorithm

playerItem.audioTimePitchAlgorithm = AVAudioTimePitchAlgorithmVarispeed;