There are many ways get snapshots from your videos. Please add your favorite! You can also get audio from your videos.
One simple way is with gxine. While it plays a video, you can save a frame with Ctrl-s. For example:
$ gxine monkey.mpg <<video opens in new window>> <<Use Ctrl-s to save a frame>>
If you pause the video and use the position slider, you can more accurately grab the exact scene you want.