First, get FFMpeg and put the bin/ffmpeg to where your victim video is.(link for Windows) Second, open up ye olde command line and cd to the directory (for convenience). Then,

ffmpeg -i "yourVideo.mp4"

This step is not strictly necessary, but it will give you info on what the encoding is:

Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'yourVideo.mp4':
Metadata:
major_brand : mp42
minor_version : 0
compatible_brands: isommp42
creation_time : 2011-06-21 01:15:31
Duration: 00:02:52.38, start: 0.000000, bitrate: 4342 kb/s
Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1920x1080, 4184 kb/s, 23.98 fps, 23.98 tbr, 1k tbn, 47.95 tbc
Metadata:
creation_time : 1970-01-01 00:00:00
Stream #0:1(und): Audio: aac (mp4a / 0x6134706D), 44100 Hz, stereo, s16, 151 kb/s
Metadata:
creation_time : 2011-06-21 01:15:33

Looks like there's AAC encoded audio. So then you do:

ffmpeg -i "yourVideo.mp4" -vn -acodec copy "yourMusic.aac"

Play yourMusic.aac in a music player of your choice.