Welcome to TG.

If you go into YouTube, find the video you wish to insert (Share) into Xara, below there is normally an option to Share. (In the menu About / Share / Add To / etc menu bar)

Click on the share option. This opens a further menu Share this Video / Embed / Email

Click on Embed option. This will give you the iframe code to paste into a Xara placeholder Body html.

Just below this is the option to set the video size. From the drop-down menu select the one you desire. This changes the iframe text.

Select the text, copy & paste into a placeholder in Xara.