The open-source community has created this amazing audio/video conversion tool called ffmpeg (windows download available here) that will take just about any filetype and convert it to another type, including stripping the audio from video.
In order to facilitate mass conversion, I ended up making a nice batch script that accepts multiple arguments (in the form of multiple files dragged onto it at once). You can download my example script here (you will need to change its extension to .bat).
ffmpeg looks at the filename to determine what it will output (my script, for example, outputs MP3 files). In addition, the most important flags are
-b NNNNk (video bitrate)
-ab NNNk (audio bitrate)
BONUS: you can use ffmpeg to convert downloaded embedded videos to formats usable by other devices. I found a handy extension for Firefox, Video DownloadHelper, that works nicely for most sites. You’ll probably want to output either a .mov, .mp4, or .avi file. Don’t forget the bitrate flags!