Modify an Android App

I have an android App that I would like to do some modifications. I don't have the Source Code. The App is a music player. It scans the phone and displays the audio files. I would like to modify it from a music player to a video player. Would like to use it to stream my music videos from YouTube. Modifications: 1. The layout of the App. (Resize images) 2. Instead of scanning the phone for audio files, enable the app to get the list of music videos from an xml. I have attached the App