I would like to convert mp4 (video included) to mp3 (without video). what is the best way of doing this apart from using audacity (or similar software) and performing manual conversion (recording as the audio plays)
I've used Convert MP4 to MP3. As for me - it's good.
Try changing the extension from .mp4 to .m4a. Then open it in iTunes and convert it to an mp3.
All video-processing roads lead to Avidemux.
Drag MP4 into window. If the original audio track in the MP4 file was MP3, you can go directly to ‘Audio->Save’ and get the original, untouched audio with no quality loss.
If it's not MP3 (probably AAC would be more likely), change the ‘Audio’ drop-down from ‘Copy’ to ‘MP3 (lame)’, hit ‘Configure’ to set the bitrate (you probably also want to enable Joint Stereo), and then ‘Audio->Save’.
Command-line-wise, there's always ffmpeg:
ffmpeg -i input.mp4 -c:a libmp3lame -q:a 4 output.mp3
-q:a determines the audio quality of the MP3; its meaning differs between encoders, but in this case a lower number gives better quality, but a larger file. See here for a guide to encoding MP3s with ffmpeg. Since the MP3 format cannot contain any video, there is no need to specify any video-stripping option - ffmpeg does it automatically.
Alternatively, to simply extract the audio into an audio MP4 (M4A):
ffmpeg -i input.mp4 -vn -c copy output.m4a
Since the MP4 format (and M4A is simply a renamed MP4) can contain video, the
-vn option is necessary to strip the video stream.
-c copy tells ffmpeg to copy the streams without any re-encoding.
You can get ffmpeg from the Downloads page on their website.
All of the above are good choices.
You may also want to investigate MeGUI - it's complex and the learning curve is not the most accessible, but it's powerful and you may find it useful again at some point in the future.