I just copied the embed code from a node-red video on YouTube.
The template node accepts moustache elements so you can pass in variables but I haven't done that.
[{"id":"be62e300.9efb1","type":"ui_tab","z":"7d1271a1.e054f","name":"Home","icon":"dashboard","order":"1"},{"id":"6c848da1.b7a08c","type":"ui_template","z":"7d1271a1.e054f","tab":"be62e300.9efb1","name":"","group":"","order":1,"format":"<iframe width=\"854\" height=\"480\" src=\"
https://www.youtube.com/embed/5I3xyc--n5A\" frameborder=\"0\" allowfullscreen></iframe>","storeOutMessages":true,"fwdInMessages":true,"x":340,"y":180,"wires":[[]]}]