It’s pretty easy to extract just the audio from a DVD in Linux, using Mplayer, sox, and either Audacity or split.

1. First you need to get the audio from the DVD into a WAV file:

    mplayer -vo null -ao pcm -aofile FILE_TO_CREATE.wav dvd://
   

   This step will take a while.

2. Next you need to convert that huge WAV file (around 1Gb for 1.5 hours) into a format that’s more compact. I prefer OGG myself:

    sox -t wav THE_WAV_FILE.wav -t ogg FILE_TO_CREATE.ogg
   

   This step will also take a while.

3. Now all that’s left is breaking that long .ogg file into separate songs. I recommend Audacity for this, as it has a GUI and has some useful features, such as being able to amplify sounds that are too soft. However, you can also use the command-line tool split, as follows:

    split -b SIZE THE_OGG_FILE.ogg NAME_TO_BEGIN_EACH_CHUNK_WITH
   

   This method is much less convenient as it only breaks your .ogg into separate files of size SIZE, ignoring the content. With Audacity, you can use your mouse to select sections and then export them to their own files.

I’m using Mplayer 1.0pre5-3.3.4, Audacity 1.2.3, sox 12.17.7, and split 5.2.1.