It depends. Royalty free does not mean free. It usually means that instead of paying an ongoing fee (royalty) you aquire it for a one time fee. Usually, even though paying the fee means you can use the work commercially, it does not mean you can use the work if you obtained it from somebody that doesn't have resell rights. For example, Bob pays the free to get a music loop and posts it on his site. He is allowed to do that. He is even allowed to sell it. You go to his website and download it. You can only use it for personal, non-commercial use because you did not pay the fee to the copyright holder. If you got the loop from the same source as Bob, then you can use it in other ways. Even though uploading a video to YouTube is usually not directly commercial, it is a form of distribution (which is protected by copyright). So unless you paid the fee then you can't use it that way. Some royalty free items are actually offered completely free. You have to read the exact licesne under which the work was released. Royalty free is a very broad term and there is no single answer to your question, but generally there is still a fee you need to pay before you can use it in the fashion you want to.
Thank you very much bluegrass special, In my case I will pay for it, but the problem is if someone download it and start to distribute it.I've seen many videos with royalty free uploaded on youtube(some of them may be not legal), but if I pay for royalty free than am I OK to upload it on youtube and other similar sites? Also is it good idea to disallow option for embed, or I can allow embed option? And also if the images contain photos of people, is that the same case or not?
If you pay the initial fee then you are fine. You are not responsible for what others do with it. You can have the embed code available. If the images are of people in public places then you do not need permission from them.