Interactive streaming is simply "on-demand" streaming, allowing a user to listen to a recording at their request via digital transmission. An example of interactive streaming would be including a music player on your website that allows a user to scroll through tracks and start/stop at their request, without having to download an audio file (i.e. MySpace, Rhapsody, Spotify).
Limelight's interactive streaming license is for audio-only recordings. If you're looking to post to YouTube, you should secure a synchronization license direct from the music publisher(s) instead.