Quais são as diferenças e semelhanças entre ffmpeg, libav e avconv?

Quando executo ffmpegno Ubuntu, ele mostra: $ ffmpeg ffmpeg version v0.8, Copyright (c) 2000-2011 the Libav developers built on Feb 28 2012 13:27:36 with gcc 4.6.1 This program is not developed anymore and is only provided for compatibility. Use avconv instead (see Changelog for the list of...