title: AVFoundation I use setActiveVideoMinFrameDuration didn't work
body: <p>I use <code>AVCaptureVideoDataOutput</code> in my demo ,for take photos in loop (like scanner) without sound,
  so i set fps to low Level</p>
  
  <pre><code>[device setActiveVideoMinFrameDuration:CMTimeMake(1, 1)];
  [device setActiveVideoMaxFrameDuration:CMTimeMake(1, 1)];
  </code></pre>
  
  <p>In my code, then do this</p>
  
  <pre><code>- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer
     fromConnection:(AVCaptureConnection *)connection
  {
       NSLog(@"date");
  }
  </code></pre>
  
  <p>for check is it work, I found it print 24 times in a second,not 1 times 1 second</p>
  
  <p>PS: the device edition is iPhone 5C and iOS 8.12</p>