avconv
Install
sudo apt-get install ffmpeg
Audio
MP3 to OGG
Note: I am really not sure how good this method is (I didn’t even listen to the file):
Check the file format:
ffmpeg -i beethoven-2-1-1-pfaul.mp3
Convert the file:
ffmpeg -i beethoven-2-1-1-pfaul.mp3 -acodec vorbis -ab 192k beethoven-2-1-1-pfaul.ogg
WAV to MP3
avconv -i talk-2014-02-02.wav talk-2014-02-02.mp3
Video
Just download Transmageddon from the software centre!!
Issues
See Firefox issues ref playing OGG files, Issues.