I happened to run across several science-related videos that I had downloaded last year on my laptop computer from NDEP - National Defense Education Program. Each video is a few minutes long and can be watched on the Internet but you also have the option of downloading the videos in different formats. Many schools block YouTube so this is a nice feature and a downloaded video should run smoothly not having to depend on Internet speed. These are high-quality videos filmed at many locations and use animation to explain certain points more clearly.
There are many components to the website, LABTV are the videos but there is also a section on Personal Stories that people relate their stories of how they became a scientist. There are many more sections to the website and you can read about the origins and purpose of the program.
National Defense Education Program Link