Android application - mp3 play/download function

I have a android project. I require to add following functionality: Play/Stop button play audio mp3 file from asset location. If file is not present in asset folder then check app file directory. if not there then download from url and store it in app files directory. and play it There are time markers present for each mp3 file. When play is started, it should trigger event based on the time markers define in xml file. This xml file will be same name of mp3. eg [login to view URL] will have file1.xml. When download is in progress it should display round progress bar on top of play button like following: [login to view URL]