Without this, users are presented with this endless loop:
$ ffplay
The program ‘ffplay’ is currently not installed. You can install it by
typing:
nix-env -i ffmpeg
$ nix-env -i ffmpeg
$ ffplay
The program ‘ffplay’ is currently not installed. You can install it by
typing:
nix-env -i ffmpeg
+ adds a minimal dependency version of ffmpeg as the default
+ the current ffmpeg changes have been moved to ffmpeg-full
+ ffmpeg default 2.5 -> 2.6
+ removed ffmpeg 0.5 & 2.5 (unused versions)
Close #7160.