Instructions for OGG/Theora+Speex
Speex is an audio codec also created by the Xilph that is specific for voice data. It can compress voice far better than vorbis in regards to size. You should use it if you have video that only contains human voice and are very concerned about total file size.
The first requirement is to strip the audio file out of your existing Audio/Video file. For raw DV rips you should use