I have a use-case named "Play a Video" in my project. The video is played from a purchased webserver on which i host the video only for my application's use.Now in the "Play a Video" use-case is "File hosting server" a secondary actor?. What makes me think it's secondary is that it is external to the main system and is involved in the main use-case, but what makes me suspicious is that it doesn't provide a service to the system.
However, if the video server is not an independent system with its own use cases, you should not show it at all on your use case diagram. Use cases are not meant to show the internals of your system. Typically, if your server is just some hardware in the architecture, or some interchangeable technical component of the system under consideration, and especially if it's could not be used by any other remote system, you're certainly in this situation.
According to Oracle a primary actor is
The Actor(s) using the system to achieve a goal. The Use Case documents the interactions between the system and the actors to achieve the goal of the primary actor.
Whereas secondary actors
Actors that the system needs assistance from to achieve the primary actor’s goal.
Secondary actors may or may not have goals that they expect to be satisfied by the use case, the primary actor always has a goal, and the use case exists to satisfy the primary actor.
In this case I'd say it provides a service to the system in that it hosts and feeds the file to the end user, reducing load from the main system.
Going with the second point, file hosting servers potentially have other goals besides "play a video" and can be involved in other use cases such as "download a video", "receive uploaded video" etc.
In this case I'd say you're right in that it is a secondary actor as it's separate to the main system.