demo : https://webrtc.github.io/samples/src/content/devices/input-output/ Case : OS : macOS 10.14 , Browser : Safari 12/Safari Preview Release 58 Steps: 1. Select the “FaceTime HD Camera” for the Video source , there is video in the demo page. 2. Select the External Camera for the Video source , there is video in the demo page. 3. Select the “FaceTime HD Camera” for the Video source , there is no video in the demo page