How to merge 4 audio file in 1 audio file iOS

Question

I have created application in which i want four audio file and i have got full URL path of that audio file. Here is the code for that

//Audio 1
NSURL *outputFileUrl1 = [NSURL fileURLWithPath:outputFilePath1];
NSLog(@"Output Audio file 1 URL : %@",outputFileUrl1);

//Audio 2
NSURL *outputFileUrl2 = [NSURL fileURLWithPath:outputFilePath2];
NSLog(@"Output Audio file 2 URL : %@",outputFileUrl2);

//Audio 3
NSURL *outputFileUrl3 = [NSURL fileURLWithPath:outputFilePath3];
NSLog(@"Output Audio file 3 URL : %@",outputFileUrl3);

//Audio 4
NSURL *outputFileUrl4 = [NSURL fileURLWithPath:outputFilePath4];
NSLog(@"Output Audio file 4 URL : %@",outputFileUrl4);

Now, i want to merge this all four audio and play it as a one single audio. any code snippet will be appreciated.