本人系统为ubuntu14.04。
问题如下：
The following information may help to resolve the situation:
The following packages have unmet dependencies:
gstreamer1.0-libav : Depends: libavcodec54 (>= 6:9.1-1) but it is not going to be installed or
libavcodec-extra-54 (>= 6:9.13) but it is not going to be installed
Depends: libavformat54 (>= 6:9.1-1) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.
解决方法：
提示缺用好几个依赖，其实只是缺少了libx264-123，给出下载链接：
下载链接：https://packages.debian.org/zh-cn/wheezy/amd64/libx264-123/download
解决问题的过程：
做了如下测试：
sudo apt-get install libavcodec54
sudo apt-get install libavcodec-extra-54
sudo apt-get install libavformat54
The following packages have unmet dependencies:
libavcodec54 : Depends: libx264-123 but it is not installable
发现只缺了libx264-123这个包，google找到它，下载安装，问题解决！