When you are setting up your Registration page, you will have certain expectations on how it will look and behave with your attendees. The registration's about section gives you the ability to inform your attendees of what to expect in the event, as well as give them information about the organization, the sponsors, etc.
If your media is not playing on the registration page, there could be a number of factors to consider.
Web browsers have moved towards stricter autoplay policies in recent years which means they will not play video or audio automatically unless certain conditions are met first. You can read more about Autoplay here.
In short, your media may not play automatically. Your attendees will need to click the play button to view and hear media.
When embedding media in the about section of your registration page you want to make sure the media is able to be publicly viewed. The links you add need to be set as public, for the preview to generate correctly and for attendees to be able to play media. Once you add the URL to the content area, the preview will generate automatically for all supported media types. Once all is set accordingly, media should also play fine from the attendees' perspective.
You can find how to set privacy setting for some of the media providers below.