I am songwriter & producer working with production music for TV, Advertising, Film & YouTube. The Royalty free music you can use is available at Pond5, Motion Elements & Production Trax.
You only pay for the music once and then can use it as much as you like in your movies. All information about rights can be found at the places where you buy the songs.
There will be new music every week so my library of stock music will be filled all the time.
If there is any special genre or sound you are looking for, please contact me.