在 iPhone 上合并两个 .caf 文件

我一直在寻找答案，但似乎找不到。很多人问过，但没有人得到答案。我有一个使用 AVAudioRecorder 录制音频的应用程序。现在我只想将两个或多个录音合并到一个可以通过电子邮件发送的文件中。有谁知道如何做到这一点？

(这个答案建议使用称为音频服务队列的东西，但我对此一无所知）

这并不像您想象的那么容易。我用的是AV基础框架完全按照您要求创建的内容进行操作我是铃声。它需要从音频文件创建 AVAsset 并设置 AVExportSession。最终的结果很棒，但确实需要一些工作。以下是我们在应用程序中创建导出功能的大致方法：

- (void) setUpAndAddAudioAtPath:(NSURL*)assetURL toComposition:(AVMutableComposition *)composition {

    AVURLAsset *songAsset = [AVURLAsset URLAssetWithURL:assetURL options:nil];  

    AVMutableCompositionTrack *track = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
    AVAssetTrack *sourceAudioTrack = [[songAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];

    NSError *error = nil;
    BOOL ok = NO;

    CMTime startTime = CMTimeMakeWithSeconds(0, 1);
    CMTime trackDuration = songAsset.duration;
    CMTime longestTime = CMTimeMake(848896, 44100); //(19.24 seconds)
    CMTimeRange tRange = CMTimeRangeMake(startTime, trackDuration);

    //Set Volume
    AVMutableAudioMixInputParameters *trackMix = [AVMutableAudioMixInputParameters audioMixInputParametersWithTrack:track];
    [trackMix setVolume:0.8f atTime:startTime];
    [audioMixParams addObject:trackMix];

    //Insert audio into track
    ok = [track insertTimeRange:tRange ofTrack:sourceAudioTrack atTime:CMTimeMake(0, 44100) error:&error];
}   

上述方法从以下方法调用两次（每个音轨一次）：

- (void) exportAudio {

    AVMutableComposition *composition = [AVMutableComposition composition];
    audioMixParams = [[NSMutableArray alloc] initWithObjects:nil];

    //Add Audio Tracks to Composition
    NSString *URLPath1 = pathToYourAudioFile1;
    NSURL *assetURL1 = [NSURL fileURLWithPath:URLPath1];
    [self setUpAndAddAudioAtPath:assetURL1 toComposition:composition];

    NSString *URLPath2 = pathToYourAudioFile2;
    NSURL *assetURL2 = [NSURL fileURLWithPath:URLPath2];
    [self setUpAndAddAudioAtPath:assetURL2 toComposition:composition];

    AVMutableAudioMix *audioMix = [AVMutableAudioMix audioMix];
    audioMix.inputParameters = [NSArray arrayWithArray:audioMixParams];

    //If you need to query what formats you can export to, here's a way to find out
    NSLog (@"compatible presets for songAsset: %@",
            [AVAssetExportSession exportPresetsCompatibleWithAsset:composition]);

    AVAssetExportSession *exporter = [[AVAssetExportSession alloc]
                                  initWithAsset: composition
                                  presetName: AVAssetExportPresetAppleM4A];
    exporter.audioMix = audioMix;
    exporter.outputFileType = @"com.apple.m4a-audio";
    NSString *fileName = @"someFilename";
    NSString *exportFile = [[util getDocumentsDirectory] stringByAppendingFormat: @"/%@.m4a", fileName];    

    // set up export 
    myDeleteFile(exportFile);
    NSURL *exportURL = [NSURL fileURLWithPath:exportFile];
    exporter.outputURL = exportURL; 

    // do the export
    [exporter exportAsynchronouslyWithCompletionHandler:^{
            int exportStatus = exporter.status;
            switch (exportStatus) {
                case AVAssetExportSessionStatusFailed: 
                    NSError *exportError = exporter.error;
                    NSLog (@"AVAssetExportSessionStatusFailed: %@", exportError);
                    break;

                case AVAssetExportSessionStatusCompleted: NSLog (@"AVAssetExportSessionStatusCompleted"); break;
                case AVAssetExportSessionStatusUnknown: NSLog (@"AVAssetExportSessionStatusUnknown"); break;
                case AVAssetExportSessionStatusExporting: NSLog (@"AVAssetExportSessionStatusExporting"); break;
                case AVAssetExportSessionStatusCancelled: NSLog (@"AVAssetExportSessionStatusCancelled"); break;
                case AVAssetExportSessionStatusWaiting: NSLog (@"AVAssetExportSessionStatusWaiting"); break;
                default:  NSLog (@"didn't get export status"); break;
    }
}];

    // start up the export progress bar
    progressView.hidden = NO;
    progressView.progress = 0.0;
    [NSTimer scheduledTimerWithTimeInterval:0.1
                                 target:self
                               selector:@selector (updateExportProgress:)
                               userInfo:exporter
                                repeats:YES];

}