title: calculate full album length
body: <p>I need to get the full length of an album that is on a device but don't get the correct result. What I have is the follwing to get an Array with the songs of one album:</p>
  
  <pre><code>MPMediaPropertyPredicate *albumNamePredicate = [MPMediaPropertyPredicate predicateWithValue:albumTitle
                                   forProperty: MPMediaItemPropertyAlbumTitle];
  MPMediaQuery *myAlbumQuery = [[MPMediaQuery alloc] init];
  [myAlbumQuery addFilterPredicate: albumNamePredicate];
  songsAlbumList = [myAlbumQuery items];
  </code></pre>
  
  <p>To get the length of a song, I use this:</p>
  
  <pre><code>NSNumber *songTrackLength = [song valueForProperty:MPMediaItemPropertyPlaybackDuration];
  int minutes = floor([songTrackLength floatValue] / 60);
  int seconds = trunc([songTrackLength floatValue] - minutes * 60);
  TracklengthLabel.text = [NSString stringWithFormat:@"%d:%02d", minutes, seconds];
  </code></pre>
  
  <p>So the above works fine, I just do not get a correct addition of the songdurations ... Any ideas?</p>