title: ReplayKit doesn't work when work with webrtc
body: <p>I use WebRtc to create a peer to peer connection to share video and audio. i want to use replaykit to record Screen &amp; Microphone.if i start recording after the peer connection has been established which means the two can share video and audio from each other.in this case,repalykit failed to record Screen &amp; Microphone and previewController was black.if i start to record before connection has been established replaykit works well.if i choose record screen only or don't add <code>RTCAudioTrack</code>,it works all the time.<br>
  So how to use replaykit with webrtc?<br>
  You can start to test with <a href="https://github.com/ISBX/apprtc-ios" rel="nofollow noreferrer">apprtc-ios</a></p>