Crop camera preview for TextureView

I have a TextureView with a fixed width and height and I want to show a camera preview inside of it. I need to crop the camera preview so that it doesn't look stretched inside my TextureView. How to do the cropping? If I need to use OpenGL, how to tie the Surface Texture to OpenGL and how to do the cropping with OpenGL?

public class MyActivity extends Activity implements TextureView.SurfaceTextureListener 
{

   private Camera mCamera;
   private TextureView mTextureView;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_options);

    mTextureView = (TextureView) findViewById(R.id.camera_preview);
    mTextureView.setSurfaceTextureListener(this);
}

@Override
public void onSurfaceTextureAvailable(SurfaceTexture surface, int width, int height) {
    mCamera = Camera.open();

    try 
    {
        mCamera.setPreviewTexture(surface);
        mCamera.startPreview();
    } catch (IOException ioe) {
        // Something bad happened
    }
}

@Override
public boolean onSurfaceTextureDestroyed(SurfaceTexture surface) {
    mCamera.stopPreview();
    mCamera.release();
    return true;
}

@Override
public void onSurfaceTextureSizeChanged(SurfaceTexture surface, int width, int height) {
}

@Override
public void onSurfaceTextureUpdated(SurfaceTexture surface)
 {
    // Invoked every time there's a new Camera preview frame
 }
}

Also, after doing the preview correctly, I need to be able to read in real-time the pixels found in the center of the cropped image.