Does anyone know of any good FREE Program that converts MP4 (or any video) to MP3?
I don't know how to do it with Audacity, if it's possible to do it with audacity, can you tell me how?
You need a version of audacity that uses the ffmpeg libraries (more info
HERE). With that, you should be able to import a video file the same as you would an audio file.
If you want more flexibility, you might try a static ffmpeg build from
http://ffmpeg.zeranoe.com/builds/. By way of example, the typical .mp4 file contains H264 video and AAC audio. If you merely want to listen to the audio on a device that supports AAC (e.g. something running rockbox or beginning with the letter "i"), you can extract the audio without modification with a command like:
ffmpeg -vn -i somevideo.mp4 -acodec copy myaudio.m4a
ffmpeg also can do all sorts of A/V transcoding. It's way too complicated to go into in detail, but if you
must convert to mp3 (sigh), you could use:
ffmpeg -vn -i somevideo.mp4 -acodec libmp3lame -ab (desired bitrate) myaudio.mp3
assuming that LAME is built in, or just:
ffmpeg -vn -i somevideo.mp4 myaudio.wav
for a PCM .wav file you can then process with audacity or something else.