title: CMTimeMake crash when making video thumbnail
body: <p>I'm trying to make a video thumbnail, and was following another tutorial here on SO. I'm sure I've done everything it told me to do, but it's still not working...</p>
  
  <p>This is the error I get:</p>
  
  <pre><code>Undefined symbols for architecture armv7:
  "_CMTimeMake", referenced from:
    -[MainMenuController imagePickerController:didFinishPickingMediaWithInfo:] in MainMenuController.o
  ld: symbol(s) not found for architecture armv7
  clang: error: linker command failed with exit code 1 (use -v to see invocation)
  </code></pre>
  
  <p>The code:</p>
  
  <pre><code>AVURLAsset* asset = [AVURLAsset URLAssetWithURL:[NSURL URLWithString:movieUrl] options:nil];
      AVAssetImageGenerator* imageGenerator = [AVAssetImageGenerator assetImageGeneratorWithAsset:asset];
      pickedImage = [UIImage imageWithCGImage:[imageGenerator copyCGImageAtTime:CMTimeMake(1, 1) actualTime:nil error:nil]];
  </code></pre>
  
  <p>Do any of you have any idea of what might be wrong?</p>
  
  <p>I have included the AVFoundation Framework, just fyi...</p>
  
  <p>Thanks in advance, Tom</p>