With Webex Events in its current form, when you push the share button, you have the option to Share File. You will be prompted to select a file and are able to share any video file on your desktop just fine with audio. However, if you plan on recording this event, the recording will not include the file you shared on screen.
NOTE: Currently, you cannot share a youtube video or video embedded in a PowerPoint with audio. Share File is the only option to work at this very moment.
As Goswin mentioned, be on the lookout for the upcoming updates to Webex Events. The action of sharing a video with sound will be much simpler and smoother.
