title: AVAssetExportSession with outputFileType m4a not working iOS13
body: <p><strong>I Suspect Xcode 11 with iOS13 not working Xcode 10.2.1 with iOS12.2 working fine</strong></p>
  
  <p>I trying to merge two audio file into one audio file. </p>
  
  <p>Bellow code working fine Xcode 10.2.1 with iOS 12.2  but now working xcode 11 with iOS13</p>
  
  <pre><code>   @objc func applyMergeAudio(){
  
          playmerge(audio1: Bundle.main.url(forResource: "audio0", withExtension: "mp3")!,audio2: Bundle.main.url(forResource: "Asteroid_Sound", withExtension: "mp3")!)
      }
  
      func playmerge(audio1: URL, audio2:  URL)
      {
          let composition = AVMutableComposition()
          let compositionAudioTrack1:AVMutableCompositionTrack = composition.addMutableTrack(withMediaType: AVMediaType.audio, preferredTrackID: CMPersistentTrackID())!
          let compositionAudioTrack2:AVMutableCompositionTrack = composition.addMutableTrack(withMediaType: AVMediaType.audio, preferredTrackID: CMPersistentTrackID())!
  
          let documentDirectoryURL = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!
          let fileDestinationUrl = documentDirectoryURL.appendingPathComponent("resultmerge.m4a")
  
          let filemanager = FileManager.default
          if (!filemanager.fileExists(atPath: fileDestinationUrl.path))
          {
              do
              {
                  try filemanager.removeItem(at: fileDestinationUrl)
              }
              catch let error as NSError
              {
                  NSLog("Error: \(error)")
              }
          }
  
          let avAsset1 = AVURLAsset(url: audio1, options: nil)
          let avAsset2 = AVURLAsset(url: audio2, options: nil)
  
          var tracks1 = avAsset1.tracks(withMediaType: AVMediaType.audio)
          var tracks2 = avAsset2.tracks(withMediaType: AVMediaType.audio)
  
          let assetTrack1:AVAssetTrack = tracks1[0]
          let assetTrack2:AVAssetTrack = tracks2[0]
  
          let duration1: CMTime = assetTrack1.timeRange.duration
          let duration2: CMTime = assetTrack2.timeRange.duration
  
          let timeRange1 = CMTimeRangeMake(start: CMTime.zero, duration: duration1)
          let timeRange2 = CMTimeRangeMake(start: CMTime.zero, duration: duration2)
          do
          {
              try compositionAudioTrack1.insertTimeRange(timeRange1, of: assetTrack1, at: CMTime.zero)
              try compositionAudioTrack2.insertTimeRange(timeRange2, of: assetTrack2, at: CMTime.zero)
          }
          catch
          {
              print(error)
          }
  
          //below line force unwarp Version xcode 10.2.1 working fine with iOS12.2. but xcode 11 with iOS13 got crush . .
          let assetExport = AVAssetExportSession(asset: composition, presetName: AVAssetExportPresetAppleM4A)
          assetExport?.outputFileType = AVFileType.m4a
          assetExport?.outputURL = fileDestinationUrl
          assetExport?.exportAsynchronously(completionHandler:
              {
                  //xcode 11 with iOS13 not fire this block but xcode 10.2.1 with iOS12.2 working fine.
                  print(fileDestinationUrl)
          })
      }
  </code></pre>
  
  <p>so would you tell me any alternative solution or did i miss anything?. </p>