iOS-更改每个AVAssetTrack的音量

我有一些音频文件需要插入到

AVMutableComposition

中。每个音频都有不同的音量。为此，我为每个音频文件创建了一个

AVMutableTrackComposition

和一个

AVAssetTrack

。因此，我使用

AVMutableAudioMix

的实例更改每个曲目的音量

let composition = AVMutableComposition()
var trackMixArray = NSMutableArray()

for audio in layer{
   let trackAudio:AVMutableCompositionTrack = composition.addMutableTrackWithMediaType(AVMediaTypeAudio, preferredTrackID: CMPersistentTrackID())

   let file = project.stringByAppendingPathComponent(audio.name)
   let soundAsset = AVURLAsset(URL: NSURL(fileURLWithPath: file), options: option as [NSObject : AnyObject])
   let sounds = soundAsset.tracksWithMediaType(AVMediaTypeAudio)
   var sound:AVAssetTrack = sounds[0] as! AVAssetTrack
   let duration:CMTime = sound.timeRange.duration

   let audioTimeRange:CMTimeRange = CMTimeRangeFromTimeToTime(kCMTimeZero, duration)
   let start:CMTime = CMTimeMakeWithSeconds(audio.start.toDouble()!, 600)
   let stop:CMTime = CMTimeMakeWithSeconds(audio.stop.toDouble()!, 600)

   let trackMix = AVMutableAudioMixInputParameters(track: trackAudio)
   trackMix.setVolume(audio.volume, atTime: kCMTimeZero)
   trackMixArray.addObject(trackMix)

   trackAudio.insertTimeRange(audioTimeRange, ofTrack: sound, atTime: start, error: nil)
 }

let audioMix = AVMutableAudioMix()
audioMix.inputParameters = trackMixArray as [AnyObject]

使用单个

AVMutableCompositionTrack

以及与其关联的更多

AVAssetTrack

不允许我更改每个曲目的音量

 let trackMix = AVMutableAudioMixInputParameters(track: sound)
 trackMix.setVolume(audio.volume, atTime: kCMTimeZero)
 trackMixArray.addObject(trackMix)

---

可以直接从

AVAssetTrack

更改音量？

您所说的“不允许我更改每个曲目的音量”是什么意思？“直接改变音量”是什么意思？清楚地解释你想做什么。我可以更改每个AVMutableCompositionTrack的音量，但不能更改每个AVAssetTrack的音量。为此，我必须将每个AVAssetTrack分配给AVMutableCompositionTrack，并更改AVMutableCompositionTrack中的卷。我的目标是使用单个AVMutableCompositionTrack，因为使用它会降低AvPlayerItem的声明速度。我仍然没有看到问题。您已经很好地解释了如何设置资产跟踪的首选卷，方法是将其下拉到可变组合跟踪子类，在该子类中它是可变的。那就这么做吧。可变组合轨迹是资产轨迹；可以在任何可以使用后者的地方使用前者。子类。看到了吗？这会更改每个AVMutableCompositionTrack的卷，而不是每个AVAssetTrack的卷

    AVMutableComposition *collageComposition = [[AVMutableComposition alloc]init];
        ...
        Some Magic
        ...
    NSArray *tracksToDuck = [collageComposition tracksWithMediaType:AVMediaTypeAudio];
            audioMix = [AVMutableAudioMix audioMix];
            NSMutableArray *trackMixArray = [NSMutableArray array];
            for (int i = 0; i < [tracksToDuck count]; i++) {
                AVMutableAudioMixInputParameters *trackMix = [AVMutableAudioMixInputParameters audioMixInputParametersWithTrack:[tracksToDuck objectAtIndex:i]];
                        [trackMix setVolume:volume atTime:kCMTimeZero];
                [trackMixArray addObject:trackMix];
            }
            audioMix.inputParameters = trackMixArray;

    ... 
    AVAssetExportSession Magic
    ...
    generalExporter = [[AVAssetExportSession alloc] initWith...
    generalExporter.audioMix = audioMix;

 - (void)setVolumeRampFromStartVolume:(float)startVolume
                         toEndVolume:(float)endVolume
                           timeRange:(CMTimeRange)timeRange