Generally, poor network conditions can manifest as black streams. Please follow the below listed actions to troubleshoot this issue.
1. Please check whether your network and connection status are stable. If not, switch to a more stable network.
2. Check if you're able to reproduce this issue on our Sample App. If not, this may be an implementation issue on your end.
3. Check that your app has been granted the requisite permission to access your camera.
4. Check that you have not accidentally muted the video stream.
5. Check that you're using the latest SDK version.
6. If this issue is only observed after concluding a screen-sharing session, try restarting the app.
7. Ensure that background applications which may be draining device resources are closed and test again.
Please include the following information:
Other Video Troubleshooting Documentation you may wish to see