title: Is mBytesPerFrame needed in AudioStreamBasicDescription?
body: <p>In <code>AudioStreamBasicDescription</code> struct:</p>
  
  <pre><code>struct AudioStreamBasicDescription {
      Float64 mSampleRate;
      UInt32  mFormatID;
      UInt32  mFormatFlags;
      UInt32  mBytesPerPacket;
      UInt32  mFramesPerPacket;
      UInt32  mBytesPerFrame;
      UInt32  mChannelsPerFrame;
      UInt32  mBitsPerChannel;
      UInt32  mReserved; 
  };
  </code></pre>
  
  <p>if we know nChannelsPerFrame and mBitsPerChannels, we can calculate mBytesPerFrame like this:
  <code>mBytesPerFrame = mBitsPerChannels * mChannelsPerFrame / 8</code> (correct me if I'm wrong)</p>
  
  <p>I believe that all of the fields exist for some reason. What is it for mBytesPerFrame?</p>