Dead handy, this:

ffmpeg -ss 0.5 -i inputfile.mp4 -t 1 -s 480x300 -f image2 imagefile.jpg

The various options:

• -t 1: limit to 1 frame extracted
• -ss 0.5: point of movie to extract from (ie seek to 0.5 seconds)
• -s 480x300: frame size of image to output (image resized to fit dimensions)
• -f image2: forces format

I use this to generate preview stills for jwplayer to use. Dead handy!