title: VTCompressionSessionCreate works on iOS 9 but not on iOS 8
body: <p>These simple lines of code (nothing else whatsoever in the app) work fine on iOS 9 (iPhone 6 and iPhone 4S), but not on iOS 8 (iPhone 5 and iPod Touch 5G):</p>
  
  <pre><code>VTCompressionSessionRef videoEncoder;
  OSStatus err = VTCompressionSessionCreate(NULL, 1920, 1080,
                                            kCMVideoCodecType_H264, 
                                            NULL, 
                                            NULL, 
                                            NULL, 
                                            NULL, 
                                            (__bridge void*)self, &amp;videoEncoder);
  if (err != noErr) {
      NSLog(@"Error when creating compression session : %d", (int)err);
  } else {
      NSLog(@"All systems go!");
  }
  </code></pre>
  
  <p>I have also tried with lower resolutions, tried providing some or all of the optional parameters, in all cases it works on iOS 9 and fails on iOS 8 with the error -12902 (kVTParameterErr). Nice to know that some parameter is wrong, but which one and why isn't it considered wrong on iOS 9?</p>
  
  <p>Note that VTCopyVideoEncoderList does give me a list where the avc1 (H264) encoder is present in all cases also.</p>
  
  <p>Any idea what's going on?</p>