title: Why is the only available AVAssetExportSession.outputFileType = AVFileTypeQuickTimeMovie
body: <p>I've set up an <code>AVAssetExportSession</code> with just 2 tracks of audio and no video, which plays just like I want it to in the <code>AVPlayer</code> - but as I go to export it, the only available <code>outputFileType</code> is <code>AVFileTypeQuickTimeMovie</code> - Why can't I choose an audio format?</p>
  
  <p>When I <code>NSLog(@"%@", [session supportedFileTypes]);</code> i get;</p>
  
  <pre><code>[51330:c07] (
      "com.apple.quicktime-movie"
  )
  </code></pre>
  
  <p>Here is my code;</p>
  
  <pre><code>- (AVMutableComposition *)getComposition {
      AVAsset *backingAsset = [AVAsset assetWithURL:self.urlForEightBarAudioFile];
      AVAsset *vocalsAsset = [AVAsset assetWithURL:self.recorder.url];
      AVMutableComposition *composition = [AVMutableComposition composition];
      AVMutableCompositionTrack *compositionBackingTrack = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
      AVMutableCompositionTrack *compositionVocalTrack = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
  
      AVAssetTrack *backingAssetTrack = [backingAsset.tracks objectAtIndex:0];
      AVAssetTrack *vocalsAssetTrack = [vocalsAsset.tracks objectAtIndex:0];
  
      CMTimeRange timeRange = CMTimeRangeFromTimeToTime(kCMTimeZero, backingAsset.duration);
  
      [compositionBackingTrack insertTimeRange:timeRange ofTrack:backingAssetTrack atTime:kCMTimeZero error:nil];
      [compositionVocalTrack insertTimeRange:timeRange ofTrack:vocalsAssetTrack atTime:kCMTimeZero error:nil];
  
      return composition;
  }
  
  
  - (IBAction)acceptRecording:(id)sender {
      AVAssetExportSession * session = [[AVAssetExportSession alloc] initWithAsset:[self getComposition] presetName:AVAssetExportPresetMediumQuality];
      NSURL *output = [self.urlForPathToEightBarRecordings URLByAppendingPathComponent:@"mix.mov"];
      session.outputURL = output;
      session.outputFileType = AVFileTypeQuickTimeMovie;
  
      NSLog(@"%@", [session supportedFileTypes]);
      [session exportAsynchronouslyWithCompletionHandler:^() {
          switch (session.status) {
              case AVAssetExportSessionStatusCompleted:
                  NSLog(@"It's done...hallelujah");
                  break;
  
              default:
                  break;
          }
      }];
  }
  </code></pre>