The best place to add a video to any product is to use "product description" field. This is only field TAB field that can be altered through Backend for each individual product. Other TABs are either FIXED (they shows off in all product with the same content) or they are generated automatically (related products, custom field, etc..)
So the best place is "product description" field. You can include a clickable thumbnail at the right-corner in the product description TAB which won't be annoying and it will be linked to youtube.com OR you can use lightbox or shadowbox to show these videos inside a popup window.
Regards.