A free app for Android, by GreatStuffApps.

This free tool is an audio and video converter that supports many formats. It is easy to use and the conversion is very fast. The program allows you to convert audio and video files. It supports most formats that you can find on your Android phone, including MP3, WAV, AIFF, MP4, MOV, FLV, MKV, and many more. You can even convert to and from a number of audio formats such as OGG, AAC, AC3, etc. 

The app allows you to convert between different formats in a very easy way. You can easily convert between most known formats. 

The app also allows you to do operations on your files, including reducing the size of the file, making the file smaller, and more.