How to pinch zoom in/out of a SurfaceViewRenderer from Webrtc?

I'm new to Webrtc, I have a video stream in a SurfaceViewRenderer. I'm using Amazon AWS Webrtc demo and they are using it.

 <org.webrtc.SurfaceViewRenderer
            android:id="@+id/cameraSurfaceView"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:background="@color/black" />

How I could add pinch zoom in/out? Could anyone point me in the right direction?

Thank you.