f2364772b8
Using commands such as mp3gain and aacgain is only the default for backwards-compatible reasons. However, on Nix(OS), we would have to either patch those tools into beets or rely on an impurity, so let's depend on audiotools and also default to that backend. Of course, there is also a GStreamer backend, but it comes with a hell of additional dependencies (which not only cover audio files), which is why I decided against defaulting to GStreamer and package audiotools instead (in eecd932). Signed-off-by: aszlig <aszlig@redmoonstudios.org>