There are several ways to do this.
You can seperate the complete audio track itself by using a software such as Super...save or convert it to MP3 and then cut out the section you want using mptrim
You can play the DVD and while itÂ´s playing use an audio capturing software such as Audacity to record the section you want...then save as an MP3.
Or, the simplest option: This is so simple but normally works extremely well: Your phone has an inbuilt microphone and recording software...start the DVD and push record when your F1 engine starts. Just make sure there is no-one in the room and that you are recording from a good volume level (not too loud or with too much bass otherwise it will distort). This may need 2 or 3 tries to get it right but it will work and save you lots of time.