Write an Android application

I have an android app that plays a special media format. The format allows the lyrics of a song to be displayed as the mp3 is playing. The lyrics are displayed from an LRC file which is inside the special media file. The app currently plays the files from an online catalogue. This means to use the app, you have to be online to access the online catalogue of songs. -The app does not have a feature to allow you to save the songs on your phone. -The app does not have a feature to allow you to play files from the SDcard. I have purchased somes files of the special media format that I would like to play on my phone. Unfortunately, the version of the official app available to play the media files, as stated above, does not have a function to allow the user to play local files. (files stored on your SDcard) I would like to be able to play files that I have saved on my phone's Sd card. This means that I will be able to use the app when am offline, since I will be playing the songs from my SDcard. Requirements: 1. Decompile the app, to analyse and understand how it decodes and plays the special media files. 2. Add a functionality for the app to also play local files stored on the SDcard. I have attached one media file and more info including a link to the app. I am open to your professional recommendation: If it would be best to add the functionality to play local files on the existing app or If it would be best to develop a fresh app, that works offline.