title: How to add interactive UIView (e.g. countdown timer) in a CoreVideo live streaming session
body: <p>I am following a sample swift code that initiates a Facebook live streaming session from iPhone:</p>
  
  <pre><code>override func viewDidLoad() {
      super.viewDidLoad()
  
      liveButton.layer.cornerRadius = 15
  
      session = VCSimpleSession(videoSize: CGSize(width: 1280, height: 720), frameRate: 30, bitrate: 4000000, useInterfaceOrientation: false)
      contentView.addSubview(session.previewView)
      session.previewView.frame = contentView.bounds
      session.delegate = self
  }
  
  func startFBLive() {
      if FBSDKAccessToken.current() != nil {
          FBLiveAPI.shared.startLive(privacy: livePrivacy) { result in
              guard let streamUrlString = (result as? NSDictionary)?.value(forKey: "stream_url") as? String else {
                  return
              }
              let streamUrl = URL(string: streamUrlString)
  
              guard let lastPathComponent = streamUrl?.lastPathComponent,
                  let query = streamUrl?.query else {
                      return
              }
  
              self.session.startRtmpSession(
                  withURL: "rtmp://rtmp-api.facebook.com:80/rtmp/",
                  andStreamKey: "\(lastPathComponent)?\(query)"
              )
  
              self.livePrivacyControl.isUserInteractionEnabled = false
          }
      } else {
          fbLogin()
      }
  }
  </code></pre>
  
  <p>This code will stream camera video feed to Facebook correctly. </p>
  
  <p>However, how should I overlay a UIView, e.g. a countdown text ontop of the camera feed? I did not mean showing the UIView locally on the phone, I meant overlaying the UIView into the video feed so that the UIView gets streamed into Facebook Live stream and will be visible by other live stream viewers on other devices.</p>
  
  <p>I can see that VCSimpleSession has this method: </p>
  
  <pre><code>addPixelBufferSource: (UIImage*) image
                       withRect: (CGRect) rect;
  </code></pre>
  
  <p>But this is probably not what I want since I need to add a countdown text...Any ideas?</p>