As a complementary answer, with a command that doesn't need the specific name of the file.
For a video containing aac audio:
avconvffmpeg -i "$0" -map 0:1 -c:a copy "${0%%.*}".m4a To use in a context menu command, a form like this works:
bash -c 'avconv'ffmpeg -i "$0" -map 0:1 -c:a copy "${0%%.*}".m4a' %f Replace with corresponding audio format output for other video format input.
Initial source here.