Fix missing id error

PiperOrigin-RevId: 469750922

demos/gl/src/main/java/androidx/media3/demo/gl/MainActivity.java

@@ -15,6 +15,8 @@
  */
  */
 package androidx.media3.demo.gl;
 package androidx.media3.demo.gl;
 
 
+import static androidx.media3.common.util.Assertions.checkNotNull;
+
 import android.app.Activity;
 import android.app.Activity;
 import android.content.Context;
 import android.content.Context;
 import android.content.Intent;
 import android.content.Intent;
@@ -83,7 +85,8 @@ public final class MainActivity extends Activity {
     VideoProcessingGLSurfaceView videoProcessingGLSurfaceView =
     VideoProcessingGLSurfaceView videoProcessingGLSurfaceView =
         new VideoProcessingGLSurfaceView(
         new VideoProcessingGLSurfaceView(
             context, requestSecureSurface, new BitmapOverlayVideoProcessor(context));
             context, requestSecureSurface, new BitmapOverlayVideoProcessor(context));
-    FrameLayout contentFrame = findViewById(R.id.exo_content_frame);
+    checkNotNull(playerView);
+    FrameLayout contentFrame = playerView.findViewById(R.id.exo_content_frame);
     contentFrame.addView(videoProcessingGLSurfaceView);
     contentFrame.addView(videoProcessingGLSurfaceView);
     this.videoProcessingGLSurfaceView = videoProcessingGLSurfaceView;
     this.videoProcessingGLSurfaceView = videoProcessingGLSurfaceView;
   }
   }