If you have 10,000 visitors per day and each one of them played the entire length of the 40 second video that would be 400,000 seconds of playback, assuming that it was evenly distributed throughout the day.
A day has 86,400 seconds, so dividing that the two means that you would be serving an average of 4.629 requests per second of playbook. 4-5 requests per seconds is very low overhead so you shouldn't worry too much, it really depends on the type of videos you are serving.
If its just mp4 or anything static you can setup nginx as a web server and it will easily handle that load without issue. Especially if the videos you are serving can all be cached because either it's a small number of videos or they are low in the file size.
Given how modern browsers and mobile devices work just serving it up as mp4 usually gives you good playback without issue and then for embedding it into a webpage you can use any number of players or other methods to get it integrated.
Or as one of the comments suggested you can offload it entirely to Vimeo, YouTube, or any other hosted video service.
I'd say spin up a 1GB droplet just to give yourself a bit of buffer, install nginx, and go from there.