iOS AVFoundation Export Session is missing audio

Here is the complete code which solved this, it has two videos whcih are combined with their audios:-

AVURLAsset* video1 = [[AVURLAsset alloc]initWithURL:[NSURL fileURLWithPath:path1] options:nil];AVURLAsset* video2 = [[AVURLAsset alloc]initWithURL:[NSURL fileURLWithPath:path2] options:nil];if (video1 !=nil && video2!=nil) {    // 1 - Create AVMutableComposition object. This object will hold your AVMutableCompositionTrack instances.    AVMutableComposition *mixComposition = [[AVMutableComposition alloc] init];    // 2 - Video track    AVMutableCompositionTrack *firstTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo                                                                        preferredTrackID:kCMPersistentTrackID_Invalid];    AVMutableCompositionTrack *firstTrackAudio = [mixComposition addMutableTrackWithMediaType:AVMediaTypeAudio                                                                        preferredTrackID:kCMPersistentTrackID_Invalid];    [firstTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, video1.duration)                        ofTrack:[[video1 tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] atTime:kCMTimeZero error:nil];    [firstTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, video2.duration)                        ofTrack:[[video2 tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] atTime:video1.duration error:nil];

// it has an audio track

    if ([[video1 tracksWithMediaType:AVMediaTypeAudio] count] > 0)    {        AVAssetTrack *clipAudioTrack = [[video1 tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];        [firstTrackAudio insertTimeRange:CMTimeRangeMake(kCMTimeZero, video1.duration) ofTrack:clipAudioTrack atTime:kCMTimeZero error:nil];    }

// it has an audio track

    if ([[video2 tracksWithMediaType:AVMediaTypeAudio] count] > 0)    {        AVAssetTrack *clipAudioTrack = [[video2 tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];        [firstTrackAudio insertTimeRange:CMTimeRangeMake(kCMTimeZero, video2.duration) ofTrack:clipAudioTrack atTime:video1.duration error:nil];    }

// export session

    AVAssetExportSession *exporter = [[AVAssetExportSession alloc] initWithAsset:mixComposition                                                                      presetName:AVAssetExportPresetHighestQuality];    //Creates the path to export to  - Saving to temporary directory    NSString* filename = [NSString stringWithFormat:@"Video_%d.mov",arc4random() % 1000];    NSString* path = [NSTemporaryDirectory() stringByAppendingPathComponent:filename];    //Checks if there is already a file at the output URL.      if ([[NSFileManager defaultManager] fileExistsAtPath:path])    {        NSLog(@"Removing item at path: %@", path);        [[NSFileManager defaultManager] removeItemAtPath:path error:nil];    }    exporter.outputURL = [NSURL fileURLWithPath:path];    //Set the output file type    exporter.outputFileType = AVFileTypeQuickTimeMovie;    path3=path;    [arr_StoredDocumentoryUrls addObject:path3];    //Exports!    [exporter exportAsynchronouslyWithCompletionHandler:^{        switch (exporter.status) {            case AVAssetExportSessionStatusCompleted:{                NSLog(@"Export Complete");                break;            }            case AVAssetExportSessionStatusFailed:                NSLog(@"Export Error: %@", [exporter.error description]);                break;            case AVAssetExportSessionStatusCancelled:                NSLog(@"Export Cancelled");                break;            default:                break;        }    }];}

Swift 4 version based on @Ashish's answer

let video1 = AVURLAsset(url: videoURL1)let video2 = AVURLAsset(url: videoURL2)// Create AVMutableComposition object. This object will hold your AVMutableCompositionTrack instances.let mixComposition = AVMutableComposition()guard let firstTrack = mixComposition.addMutableTrack(withMediaType: AVMediaType.video, preferredTrackID: Int32(kCMPersistentTrackID_Invalid)) else {return}guard let firstAudioTrack = mixComposition.addMutableTrack(withMediaType: AVMediaType.audio,preferredTrackID: Int32(kCMPersistentTrackID_Invalid)) else {return}do {  try firstTrack.insertTimeRange(CMTimeRangeMake(kCMTimeZero, video1.duration),                                 of: video1.tracks(withMediaType: AVMediaType.video)[0],                                 at: kCMTimeZero)} catch {  print("error handling video1")}do {  try firstTrack.insertTimeRange(CMTimeRangeMake(kCMTimeZero, video2.duration),                                 of: video2.tracks(withMediaType: AVMediaType.video)[0],                                 at: kCMTimeZero)} catch {  print("error handling video2")}// if video 1 has an audio trackif video1.tracks.count > 0 {  let clipAudioTrack = video1.tracks[0]  do {    try firstAudioTrack.insertTimeRange(CMTimeRangeMake(kCMTimeZero, video1.duration), of: clipAudioTrack, at: kCMTimeZero)  } catch {    print("error inserting audio track 1")  }}// if video 2 has an audio trackif video2.tracks.count > 0 {  let clipAudioTrack = video2.tracks[0]  do {    try firstAudioTrack.insertTimeRange(CMTimeRangeMake(kCMTimeZero, video2.duration), of: clipAudioTrack, at: video1.duration)  } catch {    print("error inserting audio track 2")  }}// Checks if there is already a file at the output URL.if FileManager.default.fileExists(atPath: "path") {  try? FileManager.default.removeItem(atPath: "path")}// Create Exporterguard let exporter = AVAssetExportSession(asset: mixComposition, presetName: AVAssetExportPresetHighestQuality) else {return}// Get pathguard let documentDirectory = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first else {return}let documentUrl = documentDirectory.appendingPathComponent("mergeVideo.mov")// Set the output file typeexporter.outputURL = documentUrlexporter.outputFileType = AVFileType.mov// Exports!exporter.exportAsynchronously {  switch exporter.status {  case .completed:    print("export completed")  case .failed:    print("export failed")  case .cancelled:    print("export candelled")  default:    break  }}

Try adding MobileCoreServices and execute.