Hi Mark, whilst you can certainly create a field in the
custom form builder allowing for the link of a YouTube video to be added, this won't display as an embedded video unless it is placed in the actual description field. So yes this would require customization of the default theme in order to allow more flexibility as to where it appears in the listing. Unfortunately there aren't really any specific tutorials available for changes such as this, and our
developer centre offers more general information about making modifications. The available tutorials for Vantage can be found
here. Thanks.