Second navigation level with pills

Not sure why I'm struggling so much with this :). We're using horizontal pills navigation on a site I'm working on (like this: http://getbootstrap.com/components/#nav-pills )

I need to add a second level of navigation within one of the navs. A second layer of pills doesn't seem like a good idea because it won't be clear that they are associated with the main selected pill (and will just looks weird visually).

Also vertical pills won't really work because I have a video taking up most of the screen and there is no more horizontal space left.

I considered a dropdown selector but the downside is that you can't see the other options without selecting the dropdown.

Does anyone have other suggestions? Any examples of this on other sites or any other stack exchange topics that may help me out?

Thanks in advance!