Sometimes, you are looking for a great spark that makes your title page or major pivot slide leap off of the screen to your audience. A video background might be just what the doctor ordered. Of course, before you attempt this, you should know that a technique like this should be used sparingly for reasons of taste, performance, and shareability.
Preparing and Inserting the Video
Your source video should be in HD quality if at all possible. There are lots of free video resources out on the web if you know where to look. You should always be sure to review licensing and give credit when it is due.
I like to choose a background that is not too busy or visually distracting that compliments the sentiment of the message. Using short, looping videos is best, as it saves on file size and allows the speaker to stay on the slide without fear of it "ending".