Modifying JAVA application running on Heroku

Summary: Problems retrieving MP3 files (stored as BASE64 values in a Postgres database) with a webservice. We want to show / download the MP3 files from our custom portal (made in Visualforce in Salesforce). Description of the environment: The data is already in a Postgres database on the Heroku platform. There is already a JAVA application running on Heroku that gives us a webservice with methods to get information from the Postgres database. But the method used to get the MP3 file and DECODE it is not working fine. The file is not in a correct format, so you cannot listen to it. We already have the JS script to include in our Visualforce page to call the download of a file, but because the file is not decoded correctly we cannot use it now. In the Portal we also have the possibility to UPLOAD and DOWNLOAD Voicefiles (that’s something different than the Voicemails). I think the same decode problems will occur there. So we also want to have that fixed / checked