During your interview with a family member, a good practice whenever they speak of military service is to ask about letters. Handwritten or telegraphs are most dramatic but typed or even emails will work. Have your interviewee read a letter aloud. They don’t have to look at the camera while they read. Scan or take a picture of the letter they are reading. Ask for a photo that supports the letter, in our military example it might be their military in-uniform photo.
You can also use stock video. A simple DIY (do it yourself) would be to film a national flag waving in the wind for a military theme. However, there are great resources for stock footage that is mostly open copyright – of course, it’s ALWAYS up to you to confirm use of someone else’s work. However, personal, non-profit work (which your personal Family History Video will probably be) is relatively a safe avenue, especially if you credit the work as presented on the video or in the credits. Check out archive.org or commons.wikimedia.org. Check also the local libraries of a town or county you are researching. Within any of those resources, you can search for specific years, wars, or item (“waving flag”), etc. In the U.S., for explanations and a list of other resources, go to www.publicdomainsherpa.com. Explore. Enjoy.