音樂合并，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];
}
