Repairing media codec / packages - FEBKAC error

[Patton Echols]

I seem to have broken the multimedia codecs on this laptop running 
12.04.  The problem comes from poor prior system logs and (apparently) 
changes in the way things work since 10.04.  Sorry this is long, 
starting with some background.

Background:  What I remember from 10.04 is that to be able to view and 
transcode basically any flavor of multimedia, one needed to do several 
things: (1) enable the mediabuntu repositories; (2) install that version 
of restricted extras, w32codecs (or 64 if applicable), and other codecs 
if needed; and (3) for ffmpeg, get a version with all the needed bits 
from ffmpeg.org.  (I think I was wrong about that last bit, which is 
probably part of the problem)

I did all of the above, including use of a handy ppa of the current 
ffmpeg.  (anyone who investigates will probably see the warnings that I 
assumed were not a concern -- FEBKAC #2) After the fact, I learn by 
tracking down some error messages that 12.04 uses the avconv fork of 
ffmpeg.  Basically, lots of incompatibility.

Resolution, I'd like:  I want to restore this system to the default 
install, stripping out everything I installed correctly, then get to 
where I want to go in the correct way.

Questions:
First, How would I go about getting back to original configuration short 
of installing over top of this installation from the CD? For example, is 
there a way, once I enable the correct repositories, to force a 
reinstall, including dependencies, from the current repositories, even 
if it means "regressing" version numbers?

Second, what IS the correct way to get the bell and whistle codecs into 
12.04?

Thanks,

-- 
Patton Echols