You could give Blaze Media Pro a try, granted it is not freeware but you get to use a fully functioning program during your trial period. I have been using this ultra cool prog for about 3 years now and I know once you try it you will wanna buy it. One of it's many audio/video editing featues is called decompile video which can break down a video into a jpeg screenshot of either every frame or you can select a start and stop point. You can also convert many audio/video formats and edit mp3s & videos.
http://www.blazemp.com/