由于我安装了 Ubuntu，因此无法安装视频编解码器，我收到以下错误：以下软件包具有未满足的依赖关系：
The following packages have unmet dependencies:
gstreamer1.0-libav: Depends: libavcodec-extra-54 (>= 6:9.13) but 7:1.2.5-1~trusty1 is to be installed
Depends: libavformat54 (>= 6:9.1-1) but 7:1.2.5-1~trusty1 is to be installed
Depends: libavutil52 (>= 6:9.1-1) but 7:1.2.5-1~trusty1 is to be installed
Depends: libc6 (>= 2.14) but 2.19-0ubuntu6 is to be installed
Depends: libglib2.0-0 (>= 2.37.3) but 2.40.0-2 is to be installed
gstreamer1.0-libav:i386: Depends: libavcodec-extra-54 (>= 6:9.13) but 7:1.2.5-1~trusty1 is to be installed
Depends: libavformat54 (>= 6:9.1-1) but 7:1.2.5-1~trusty1 is to be installed
Depends: libavutil52 (>= 6:9.1-1) but 7:1.2.5-1~trusty1 is to be installed
Depends: libc6 (>= 2.7) but 2.19-0ubuntu6 is to be installed
Depends: libglib2.0-0 (>= 2.37.3) but 2.40.0-2 is to be installed
但是，我使用的是 VLC。出于某种原因，我不得不卸载 VLC，现在我无法重新安装它。当我尝试安装 VLC 时，它给出了以下错误：
The following packages have unmet dependencies:
vlc : Depends: vlc-nox (= 2.1.4-0ubuntu14.04.1) but it is not going to be installed
Recommends: vlc-plugin-notify (= 2.1.4-0ubuntu14.04.1) but it is not going to be installed
Recommends: vlc-plugin-pulse (= 2.1.4-0ubuntu14.04.1) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.
我尝试了所有解决此类问题的方法，但都不起作用。我也尝试了其他方法，aptitude但都没有用。从源代码安装也失败了。
apt-get update给了我一个错误：
W: GPG error: http://ppa.launchpad.net trusty Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 6A9653F936FD5529
答案1
问题在于签名错误。解决方法是以下命令：
gpg --keyserver keyserver.ubuntu.com --recv 6A9653F936FD5529
gpg --export --armor 6A9653F936FD5529 | sudo apt-key add -