I used Crouton to install Xubuntu 12.04.4 LTS with the XFCE environment on my HP Chromebook 11. I've gotten it all fully installed and everything; the only thing I'm doing now is the basic setup things, like adding codecs and other things like LibreOffice, VLC, Firefox, Ubuntu Software Center, etc. This information I got from 2 sources:

1. http://www.efytimes.com/e1/fullnews.asp?edid=137269
2. http://www.binarytides.com/better-xubuntu-14-04/ .

I'm currently on the same step at both URLs, which is #6 on Link 1 and #8 on Link 2.

Per the articles, which both said the same thing, I typed in

sudo apt-get install xubuntu-restricted-extras libavcodec-extra and it didn't do

anything. It just kept on saying the same thing:

Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package libavcodec-extra

I've spend the last hour or so scouring the internet for a solution, for a hint even at what is going on. I don't want to do a clean reinstall, for two reasons: 1) it's takes like 1.5h just to get the croot fully installed, and 2) everything but this out of what I've done so far (up to #6 at Link 1 & up to #8 at Link 2) works except the audio. I've already installed flash, so YouTube works fine. It's just I can't hear any audio.

Please help?

Thanks in advance. I appreciate all the great help I've been getting from AskUbuntu lately. You all are great.