Hi Diana,
Badges can be awarded on course completion. The problem with a MP4 (or whatever format you're using) is its not possible to prove the user has listened to it. What you could have is a File activity containing the soundfile set to be completed when the file is viewed then another activity, like a quiz, which asks the user to confirm they've listen to to the podcast. Set the course completion on both activities and award the badge on course completion.
hope this is useful,
cheers,
George,.