2018-06-17

音乐合并，混音

https://stackoverflow.com/questions/7656512/combining-two-caf-files-on-iphone

- (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];

} 

- (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];

}