How to extract an audio file from an mp4 using libavcodec?

I'm trying to convert an mp4 to a wav file to ultimately use pocketsphinx to convert the audio to a string that I can work with.

But right now I'm stuck on how to use libavcodec to extract the audio from the video file? Does anyone know how to do this? I looked at the documentation in the example folder of libavcodec. It has a few example files for filtering_audio and filtering_video but they are really confusing and hard to follow. Little to no documentation. I think I want the filtering_video but it seems like its working with the image frames, but what I want is the audio. Please someone help! (I'm working in C)

Thanks