In this lecture, we will build a desktop application with Tkinter. The purpose of this app is to upload an mp4 video format and convert it into an mp3 audio format. You might see this feature online, those online video converters. But today, we will create a desktop application, not a web application. 4. How to Convert MP3 to MP4 Online. If you prefer to convert MP3 to MP4 online and do not want to download any program, FileConverto is an alternative you can use. This serves as an MP3 to MP4 converter or the other way around. Moreover, you may add an MP3 song as the audio track with an image file as a background. 7soJSL.