如何更改 AVMutableComposition 中曲目的音量

Question

我一直在尝试不同的方法来解决这个问题，但它们需要很长时间才能处理（更改不同卷的 MP3 文件）。

我有一个 AVMutableComposition，其中填充了多个用于音频和视频的 AVMutableCompositionTrack。混合工作正常，但音轨音量调整不起作用，并且在导出时失败。

这是我使用的代码：

AVMutableComposition* mixComposition = [AVMutableComposition composition];
AVURLAsset *soundTrackAsset = [[AVURLAsset alloc]initWithURL:trackTempProcessedURL options:nil];

//ADDING AUDIO
AVMutableCompositionTrack *compositionAudioSoundTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:trackIDSoundTrack];
[compositionAudioSoundTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, audioAsset.duration) 
                                    ofTrack:[[soundTrackAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0] 
                                     atTime:CMTimeAdd(cmTimeDifference,startTime) error:nil];

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

//ADDING VIDEO
AVURLAsset* videoAsset = [[AVURLAsset alloc]initWithURL:frontAssetURL options:nil];
[compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, videoAsset.duration) 
                               ofTrack:[[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0]
                                atTime:startTime error:nil];

//EXPORTING
_assetExport = [[AVAssetExportSession alloc] initWithAsset:mixComposition presetName: AVAssetExportPresetPassthrough];

_assetExport.outputFileType = AVFileTypeQuickTimeMovie; 
_assetExport.outputURL = exportUrl;
_assetExport.shouldOptimizeForNetworkUse = YES;
_assetExport.audioMix = audioMix;  

[_assetExport exportAsynchronouslyWithCompletionHandler:
 ^(void ) { 
 ...

没有音频混合器，一切都混合得很好，但是当我尝试改变音量时，导出会出现错误：

AVFoundationErrorDomain Error: 11822

Answer 1

AVMutableAudioMixInputParameters 需要设置“trackID”来指示哪个音轨应应用该参数。

for (NSInteger i = 0; i < [tracksToDuck count]; i++) {
    AVMutableAudioMixInputParameters *trackMix = [AVMutableAudioMixInputParameters audioMixInputParametersWithTrack:[tracksToDuck objectAtIndex:i]];
    [trackMix setVolume:volume atTime:kCMTimeZero];   

//+++++code
    AVMutableCompositionTrack * track = [tracksToDuck objectAtIndex:i]
    [trackMix setTrackID:[track trackID]];

    [trackMixArray addObject:trackMix];
}