IOS - Merge two audios and get it as a mp3 format - ios

Question

Here I have two audio files, I successfully combined these two audio files but its return only a .m4a format, I need the mp3 format
- (BOOL) combineVoices1
{
NSError *error = nil;
BOOL ok = NO;
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
CMTime nextClipStartTime = kCMTimeZero;
//Create AVMutableComposition Object.This object will hold our multiple AVMutableCompositionTrack.
AVMutableComposition *composition = [[AVMutableComposition alloc] init];
AVMutableCompositionTrack *compositionAudioTrack = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
[compositionAudioTrack setPreferredVolume:0.8];
NSString *soundOne =[[NSBundle mainBundle]pathForResource:#"test1" ofType:#"caf"];
NSURL *url = [NSURL fileURLWithPath:soundOne];
AVAsset *avAsset = [AVURLAsset URLAssetWithURL:url options:nil];
NSArray *tracks = [avAsset tracksWithMediaType:AVMediaTypeAudio];
AVAssetTrack *clipAudioTrack = [[avAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];
[compositionAudioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, avAsset.duration) ofTrack:clipAudioTrack atTime:kCMTimeZero error:nil];
AVMutableCompositionTrack *compositionAudioTrack1 = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
[compositionAudioTrack setPreferredVolume:0.3];
NSString *soundOne1 =[[NSBundle mainBundle]pathForResource:#"test" ofType:#"caf"];
NSURL *url1 = [NSURL fileURLWithPath:soundOne1];
AVAsset *avAsset1 = [AVURLAsset URLAssetWithURL:url1 options:nil];
NSArray *tracks1 = [avAsset1 tracksWithMediaType:AVMediaTypeAudio];
AVAssetTrack *clipAudioTrack1 = [[avAsset1 tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];
[compositionAudioTrack1 insertTimeRange:CMTimeRangeMake(kCMTimeZero, avAsset.duration) ofTrack:clipAudioTrack1 atTime:kCMTimeZero error:nil];
AVMutableCompositionTrack *compositionAudioTrack2 = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
[compositionAudioTrack2 setPreferredVolume:1.0];
NSString *soundOne2 =[[NSBundle mainBundle]pathForResource:#"song" ofType:#"caf"];
NSURL *url2 = [NSURL fileURLWithPath:soundOne2];
AVAsset *avAsset2 = [AVURLAsset URLAssetWithURL:url2 options:nil];
NSArray *tracks2 = [avAsset2 tracksWithMediaType:AVMediaTypeAudio];
AVAssetTrack *clipAudioTrack2 = [[avAsset2 tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];
[compositionAudioTrack1 insertTimeRange:CMTimeRangeMake(kCMTimeZero, avAsset2.duration) ofTrack:clipAudioTrack2 atTime:kCMTimeZero error:nil];
AVAssetExportSession *exportSession = [AVAssetExportSession
exportSessionWithAsset:composition
presetName:AVAssetExportPresetAppleM4A];
if (nil == exportSession) return NO;
NSString *soundOneNew = [documentsDirectory stringByAppendingPathComponent:#"combined10.m4a"];
//NSLog(#"Output file path - %#",soundOneNew);
// configure export session output with all our parameters
exportSession.outputURL = [NSURL fileURLWithPath:soundOneNew]; // output path
exportSession.outputFileType = AVFileTypeAppleM4A; // output file type
// perform the export
[exportSession exportAsynchronouslyWithCompletionHandler:^{
if (AVAssetExportSessionStatusCompleted == exportSession.status) {
NSLog(#"AVAssetExportSessionStatusCompleted");
} else if (AVAssetExportSessionStatusFailed == exportSession.status) {
// a failure may happen because of an event out of your control
// for example, an interruption like a phone call comming in
// make sure and handle this case appropriately
NSLog(#"AVAssetExportSessionStatusFailed");
} else {
NSLog(#"Export Session Status: %d", exportSession.status);
}
}];
return YES;
}
Could any body help me please

Answer 1

You are in for a world of trouble in trying to convert to mp3's. There are expensive patent licenses involved. You can find ton's of questions of people looking for a solution to this, and no good responses.
If you are looking to just do something for yourself on your own, you can try FFMpeg, but they have some pretty serious legals disclaimers here:
This line is particularly worrisome:
Q: Is it perfectly alright to incorporate the whole FFmpeg core into
my own commercial product?
A: You might have a problem here. There
have been cases where companies have used FFmpeg in their products.
These companies found out that once you start trying to make money
from patented technologies, the owners of the patents will come after
their licensing fees. Notably, MPEG LA is vigilant and diligent about
collecting for MPEG-related technologies.