I'm not 100% sure how well this will work out for you because I'm not too sure how much the free sample of this program has. I have Adobe Premiere Pro myself and doing this is very easy.
http://www.softpedia.com/get/Multime...iere-Pro.shtml
When you import video into Adobe Premiere, the video and sound are automatically separated for easy editing. All you have to do is lock the sound to delete the video. When you're done, go to file and find Export Video. Once there, the menu that comes up allows you to choose what format you want your video and sound to be so all you need to do is scroll through the options and find what you need.
BTW. The sound mixing options on the program allow you to clean and play around with the sound levels.
Hope this helps.