You can now add Youtube videos to your profile. It will automatically play the video once you visit the profile. To add a video to your profile, find one at Youtube.com and copy the link of that page.
Now once you got the link, go to your User CP and click on Edit Your Details. Now at the bottom, you'll see 2 text boxes about Youtube. Hit the link in the first box and give it a title at the second. After that, hit Save and you're done.
For a example how it will look like, check my profile.
Edit: Auto-play switched off