First of all, make sure that the media file you are accessing is a video, not an audio track. You can check if it’s audio or video based on the icons in your book. 

For your information, currently, only this book has accompanying videos on the TTMIK: Audio app: How To Sound Like A Native Korean Speaker

If you can’t play the videos, please update your app first. If it doesn’t work, please write to us here with your device information.