“没有安装候选者，但是以下包替换它”循环
我在Ubuntu Wily上。
sudo apt-get install libavcodec56产生：
Package libavcodec56 is not available, but is referred to by another package. This may mean that the package is missing, has been obsoleted, or is only available from another source However the following packages replace it: libavcodec-extra-56
在尝试安装该软件包之前，这很好，很花哨：
Package libavcodec-extra-56 is not available, but is referred to by another package. This may mean that the package is missing, has been obsoleted, or is only available from another source However the following packages replace it: libavcodec56
这是我的sources.list ，删除了空格和注释：
deb http://us.archive.ubuntu.com/ubuntu/ wily main restricted universe multiverse deb-src http://us.archive.ubuntu.com/ubuntu/ wily main restricted universe multiverse deb http://us.archive.ubuntu.com/ubuntu/ wily-security main restricted universe multiverse deb http://us.archive.ubuntu.com/ubuntu/ wily-updates main restricted universe multiverse deb-src http://us.archive.ubuntu.com/ubuntu/ wily-security main restricted universe multiverse deb-src http://us.archive.ubuntu.com/ubuntu/ wily-updates main restricted universe multiverse deb http://archive.canonical.com/ubuntu wily partner deb-src http://archive.canonical.com/ubuntu wily partner
在Ubuntu 15.10中，我们重新引入了ffmpeg 
作为替换avconv的默认转换工具。 编解码器将由libavcodec-ffmpeg56 。
sudo apt-get install libavcodec-ffmpeg56
不再支持先前的包libavcodec56 。