Using GotoWebinar 10.13.1 Build 18705 on Win10-64, the audio of a presented movie is played on the system default speakers, not though the configured headset (where the spoken voice is heard).
@MWeus Please keep in mind that GoToWebinar video sharing will only play the audio through your speakers / headset connected to your device. We may change this functionality in the future to also include telephone callers.
I reported the devices at 10-29-2020 09:07 AM
Please note that the speakers are set as default audiodevice, the headset is configured as device only for the meeting. Since I'm an attendee I don't know the source of the video. It was some corporate promotion video I assume mp4