We had an event with short talks at the xHain Hackerspace recently and we wanted to use the club matrix as a timer for the presenter. I have yet to write a font generator and a script to do that though and the only thing I can kind of reliably do is playing a video. The sane solution: search on youtube for a 15min countdown video, which kind of worked.
But since we were at the hackerspace, one member wanted to try to let ffmpeg generate the countdown. The first version of the script by Niklas was almost perfect, but used a PNG as a background image. Then another member (danimo) took a look and removed the background image and let ffmpeg turn the background from green to red in the last minute.