http://audacity.sourceforge.net/download/
1. Open Audacity, after installing it
2. Choose input: Stereo Mix

3. Press record

4. Press play on video

5. Press stop when done recording

6. Highlight by dragging the mouse across a section of the audio.

7. Choose Effect > Reverse from the menu

8. File > Export Selection As MP3.
Done! I hope this helps everyone share in the fun.