A free app for Android, by Happy4Video Studio.
Video Converter: Video Compressor is a handy utility that is capable of converting a wide variety of video formats to MP3.
It's a very simple-to-use app that lets you convert your favorite video formats such as AVI, MKV, FLV, RMVB, WMV, MOV, MPG, and other formats to MP3. You don't need to do anything other than installing the app and start using it.
This app is designed to be very user-friendly and easy to use. The first thing you need to do is select the video you want to convert to MP3. Then, you need to select the output format and the quality. The default setting is MP4, but you can select other formats, such as AVI, MKV, FLV, RMVB, WMV, MOV, MPG, etc.