Concatenating sound files on the iPhone (m4a) fails - iphone

Question

I am trying to make one long sound file by concatenating several smaller sound files - all are in the m4a format, and the result should also be in the m4a format.
Here is the code (the audFiles array holds the names of the sound files to join).
Note I only print the file sizes for peace of mind...
CMTime nextClipStartTime = kCMTimeZero;
AVMutableComposition *combinedSounds = [AVMutableComposition composition];
NSString *tempDir = NSTemporaryDirectory();
NSArray *audFiles;
for (int i = 0; i < [audFiles count]; i++)
{
NSString *addSound = [tempDir stringByAppendingString:audFiles[i]];
if ([[NSFileManager defaultManager] fileExistsAtPath:addSound] == YES)
{
NSDictionary *fileAttributes = [[NSFileManager defaultManager] attributesOfItemAtPath:addSound error:nil];
if (fileAttributes != nil)
{
NSString *fileSize = [fileAttributes objectForKey:NSFileSize];
NSLog(#"file %# %#", addSound, fileSize);
NSURL *assetURL = [[NSURL alloc] initFileURLWithPath:addSound];
AVURLAsset *asset = [[AVURLAsset alloc] initWithURL:assetURL options:nil];
if (asset != nil)
{
CMTimeRange timeRange = CMTimeRangeMake(kCMTimeZero, asset.duration);
NSLog(#"asset %d length %lld", i, asset.duration.value);
if (asset.duration.value > 0)
{
AVAssetTrack *audTrack = [asset tracksWithMediaType:AVMediaTypeAudio][0];
AVMutableCompositionTrack *audioTrack = [combinedSounds addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
if ([audioTrack insertTimeRange:timeRange ofTrack:audTrack atTime:nextClipStartTime error:nil] == NO)
{
NSLog(#"insertTimeRange %d FAILED", i);
}
nextClipStartTime = CMTimeAdd(nextClipStartTime, asset.duration);
nextClipStartTime = CMTimeAdd(nextClipStartTime, CMTimeMake(0.1, 1));
NSLog(#"nextClipStartTime %lld", nextClipStartTime.value);
}
}
}
}
}
NSString *finalSound = [tempDir stringByAppendingString:#"result.m4a"];
AVAssetExportSession *exportSession = [[AVAssetExportSession alloc] initWithAsset:combinedSounds presetName:AVAssetExportPresetPassthrough];
NSString *exported = [tempDir stringByAppendingString:finalSound];
[[NSFileManager defaultManager] removeItemAtPath:exported error:nil];
NSURL *exportedURL = [[NSURL alloc] initFileURLWithPath:exported];
exportSession.outputURL = exportedURL;
exportSession.shouldOptimizeForNetworkUse = YES;
exportSession.outputFileType = AVFileTypeAppleM4A;
[exportSession exportAsynchronouslyWithCompletionHandler:^{
switch (exportSession.status)
{
case AVAssetExportSessionStatusFailed:
{
NSLog(#"exportSession FAIL");
break;
}
case AVAssetExportSessionStatusCompleted:
{
NSLog(#"exportSession SUCCESS");
}
}
}];
"exportSession SUCCESS" is reported, and the exported file exists and can be played, but it only contains the first of the constituent files.
Any ideas what I am doing wrong ?
Thanks.

Answer 1

Step 1 : Add AVFoundation.Framework and CoreMedia.Framework in your Project
Step 2 : #import <AVFoundation/AVFoundation.h> in your .h file
Step 3 : Write following method in your .m file
Step 4 : Call this function from ViewDidAppear to create Merged Audio file.
// Get Asset Detail
- (AVAsset *)getAvAssetForFile:(NSString *)fileName andType:(NSString *)fileType
{
NSString *URLPath = [[NSBundle mainBundle] pathForResource:fileName ofType:fileType];
NSURL *assetURL = [NSURL fileURLWithPath:URLPath];
AVAsset *asset = [AVAsset assetWithURL:assetURL];
return asset;
}
- (void)mergeAudioFiles
{
// `An Array with List of Audio Clips to be Merged, they could be of different type also`
NSMutableArray *listOfAudio = [[NSMutableArray alloc] initWithCapacity:0];
// `Create AVAsset Object from your audio files and add to array`
[listOfAudio addObject:[self getAvAssetForFile:#"audioFile1" andType:#"caf"]];
[listOfAudio addObject:[self getAvAssetForFile:#"audioFile2" andType:#"caf"]];
[listOfAudio addObject:[self getAvAssetForFile:#"audioFile3" andType:#"aiff"]];
AVMutableComposition *composition = [AVMutableComposition composition];
CMTime current = kCMTimeZero;
NSError *compositionError = nil;
for(AVAsset *asset in listOfAudio) {
BOOL result = [composition insertTimeRange:CMTimeRangeMake(kCMTimeZero, [asset duration])
ofAsset:asset
atTime:current
error:&compositionError];
if(!result) {
if(compositionError) {
// manage the composition error case
NSLog(#"Error in Merging : %#",[compositionError debugDescription]);
}
} else {
current = CMTimeAdd(current, [asset duration]);
}
}
AVAssetExportSession *exporter = [[AVAssetExportSession alloc]
initWithAsset: composition
presetName: AVAssetExportPresetAppleM4A];
exporter.outputFileType = #"com.apple.m4a-audio";
// Set Output FileName
NSString *fileName = #"myAudioTrack";
NSString *exportFile = [DOC_DIR_PATH stringByAppendingFormat: #"/%#.m4a", fileName];
// set up export
NSURL *exportURL = [NSURL fileURLWithPath:exportFile];
exporter.outputURL = exportURL;
// do the export
[exporter exportAsynchronouslyWithCompletionHandler:^{
int exportStatus = exporter.status;
switch (exportStatus) {
case AVAssetExportSessionStatusFailed: NSLog (#"AVAssetExportSessionStatusFailed: %#", exporter.debugDescription); 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;
}
}];
}