Is it an actual .wav, or are you trying to pull audio from a stream recording? Depending on what you used to capture the video depends on the codec used to record the audio alongside with video. It's going to be compressed, and may come off as a .mp3. At any rate, you can use a variety of programs (most free) that will rip the audio from a video and even convert it into a more compressed form. Hover your mousey thingie over this link:
http://www.guidingtech.com/5729/13-free-software-rip-audio-from-video/
Personally, I would recommend Audacity. It's a very simple program to learn at initiation, and with continuous use, it can start to complete your most advanced audio needs. I've used it many many many years ago to rip sound bytes from an episode of Frasier, so I know it has the capabilities to do so. Actually... it still does! Move your pointy clicker doodad over this link next:
http://www.guidingtech.com/12836/extract-audio-from-video-audacity/
If you want to rip it by using a site on the web, there are a few, but most web-based utilities limit the length and quality of the sound, so I can't really recommend those. You may want to use a program that will do this for you with no limitation and enhanced settings in the event that you plan to do this again.
-Hashtag Tuna