First add your CAST as a video source in the bottom left panel by pressing on “+” and choose Video Capture Device from the dropdown.
In the window that now opens, confirm that you want to create the new input source.
Next, choose AtomX CAST from the Devices dropdown and set the resolution to 1920x1080 to match your CAST’s output to your computer.
To set the AtomX CAST as your audio source in OBS, you need to add it to your Sources by choosing Audio Input Capture from the dropdown.
In the window that now opens, confirm that you want to create a new audio source.
Choose AtomX CAST from the Devices dropdown. Your embedded audio should now appear in the Audio Mixer panel on the bottom.
Further adjustments such as dialing in the streaming bit rate and entering the stream key can now be made via the OBS Settings.