Adding border to video

Whats the easiest way to modify a video to have a border round it?
I've seen people with 4:3 videos and adding padding to the left and right to make it 16:9
Any guides I have found on google have been people stretching the image.
Any suggestions for software that can do it?

how about camtasia

Cheers, will try the trial and see if it can do it.