我在使用 Ubuntu Wily。
sudo apt-get install libavcodec56产量：
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
在尝试安装该包之前，一切都很好：
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，去掉了空格和注释：
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
答案1
在 Ubuntu 15.10 中我们重新引入了ffmpeg 
作为默认转换工具来替换AVCONV。编解码器将由 提供libavcodec-ffmpeg56。
sudo apt-get install libavcodec-ffmpeg56
先前的包libavcodec56不再受支持。