"The ffmpeg program is only provided for script compatibility and will be removed in a future release. It has been deprecated in the Libav project to allow for incompatible command line syntax improvements in its replacement called avconv (see Changelog for details). Please use avconv instead."
libav is not the successor to ffmpeg. libav is a fork. How'd Debian move so quickly to a(n) (immature) fork?
Politics.
Basically it was a big split down the middle, the entire project split in half.
Not to kick 'em while they're down but it certainly wasn't on technical merit.
As I say to people this is like the Catholic/Protestant split, both sides think they are the one-true-ffmpeg but both have valid claims. Doesn't change the fact it's a disastrous situation and both projects are not in particularly good states.
ffmpeg is the one-true-ffmpeg. If libav surpassed ffmpeg, we'd have libav. The one-true-libav. libav doesn't have a valid claim; It's a fork second to ffmpeg.
Somebody put the cart before the horse. Happy to see it fixed.