title: Understanding CGAffineTransform Rotation
body: <p>I have a <code>AVMutableComposition</code> which i'm applying transform to fix the orientations issue.</p>
  
  <p>I solved all the others rotations cases, expect one. </p>
  
  <pre><code>else if (p.a == 0.0 &amp;&amp; p.b == 1.0 &amp;&amp; p.c == 1.0 &amp;&amp; p.d == 0.0)
          {
              p.a = 1
              p.d = -1.0
              p.c = 0
              p.b = 0
              p.tx = 0
              p.ty = originalVideoTrack.naturalSize.width
          }
  </code></pre>
  
  <p><strong>The video is in the right size &amp; shape. Tho he is missing 90 degrees rotations,in order to fit his layer. Any suggestions how can i achieve this 90 degrees rotate thru the matrix values?</strong></p>