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];
}