Why doesn't "apt-get autoremove" remove all installed dependencies?

Question

Installing libav-tools and ubuntu-restricted-extras also installs these new packages:

  cabextract chromium-codecs-ffmpeg-extra freepats gstreamer0.10-fluendo-mp3
  gstreamer0.10-plugins-bad gstreamer0.10-plugins-bad-multiverse
  gstreamer0.10-plugins-ugly gstreamer1.0-fluendo-mp3 gstreamer1.0-libav
  gstreamer1.0-plugins-bad gstreamer1.0-plugins-bad-faad
  gstreamer1.0-plugins-bad-videoparsers gstreamer1.0-plugins-ugly
  gstreamer1.0-plugins-ugly-amr libav-tools libavcodec-extra
  libavcodec-extra-56 libavdevice55 libavfilter5 libcdaudio1 libdirac-encoder0
  libfaac0 libfftw3-double3 libflite1 libgme0 libgstreamer-plugins-bad0.10-0
  libgstreamer-plugins-bad1.0-0 libgtkglext1 libilmbase6 libmimic0
  libmjpegutils-2.1-0 libmms0 libmpeg2encpp-2.1-0 libmpg123-0 libmplex2-2.1-0
  libmspack0 libofa0 libopencore-amrnb0 libopencore-amrwb0
  libopencv-calib3d2.4 libopencv-contrib2.4 libopencv-core2.4
  libopencv-features2d2.4 libopencv-flann2.4 libopencv-highgui2.4
  libopencv-imgproc2.4 libopencv-legacy2.4 libopencv-ml2.4
  libopencv-objdetect2.4 libopencv-video2.4 libopenexr6 libsidplay1 libslv2-9
  libsoundtouch0 libspandsp2 libsrtp0 libtbb2 libvo-aacenc0 libvo-amrwbenc0
  libwildmidi-config libwildmidi1 libzbar0 oxideqt-codecs-extra

However, apt-get autoremove libav-tools ubuntu-restricted-extras only removes the following:

  gstreamer0.10-plugins-bad-multiverse libav-tools libavcodec-extra
  libavdevice55 libavfilter5 libfaac0 ubuntu-restricted-extras

Why doesn't autoremove remove all packages that were installed alongside those I initially wanted installed and now want removed? How can I remove these dependencies automatically, while removing the packages they were installed along with? It looks as if I would have to somehow keep track of all the dependencies that were installed alongside each desired package, so I could remove them manually when I wanted to remove the initially desired package.

Answer 1

Note: sudo apt-get autoremove <package1> [<package2>, ...] = sudo apt-get remove --autoremove <package1> [<package2>, ...]

Meeting the dependencies for libav-tools and ubuntu-restricted-extras required to update (and not to install) most of the packages listed by sudo apt-get install libav-tools ubuntu-restricted-extras to a new version.

From the apt-get man page for Trusy:

[...]
       install
[...]
           This is also the target to use if you want to upgrade one or more
           already-installed packages without upgrading every package you have
           on your system. Unlike the "upgrade" target, which installs the
           newest version of all currently installed packages, "install" will
           install the newest version of only the package(s) specified. Simply
           provide the name of the package(s) you wish to upgrade, and if a
           newer version is available, it (and its dependencies, as described
           above) will be downloaded and installed.
[...]

This is logic, since if a package depends on a later version of an already installed package, in order to run former the latter must be updated.

The result is that if any of those already installed packages was required by any package prior to the installation of libav-tools and ubuntu-restricted-extras, it's not going to be autoremoved.

You can check this by running apt-cache rdepends <package> on each of the packages mistakenly expected to be autoremoved: each of them will be required by at least one package not going to be autoremoved.