here is result when I typed Can anyone solve my problem? after doing execute command of following
install libavcodec-extra
I realized that vlc and golden dict disappeared. some other apps may also be affected by the command but so far i have confirmed were the two.
I executed command sudo apt-get autoremove that removed some files. but still I am not able to restore my vlc and golden dict.
apt-get install vlc
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
vlc : Depends: vlc-nox (= 2.1.2-2build2) but it is not going to be installed
Depends: libvlccore7 (>= 2.1.0) but it is not going to be installed
Recommends: vlc-plugin-notify (= 2.1.2-2build2) but it is not going to be installed
Recommends: vlc-plugin-pulse (= 2.1.2-2build2) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.
When I do apt-get update I will get error of PUBLIC KEY
W: GPG error: http://archive.ubuntu.com trusty Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5 NO_PUBKEY 3B4FE6ACC0B21F32