ffmpeg

ffmpeg is a multiplatform, open-source library for video and audio files. Here are a few commands for most of your conversion needs!

Getting infos from a video file

ffmpeg -i video.avi

Turn X images to a video sequence

ffmpeg -f image2 -i image%d.jpg video.mpg

This command will transform all the images from the current directory (named image1.jpg, image2.jpg, etc…) to a video file named video.mpg.