cd and dvd ?

I have a 4 cd audiobook. I want to make a DVD that combines all 4 cds into one DVD.
I have pulled the audio out and combined them into one mp3.
the mp3 is 250megs.
I need to make some kind of blank m2v file to mplex the audio to.
How do I know how long to make the blank video?
what can I do to make the video low bitrate?
This is just to get around the constant switching out of the CDs in the car. The DVD player still plays the audio while I am driving just not the video.
thanks
I have pulled the audio out and combined them into one mp3.
the mp3 is 250megs.
I need to make some kind of blank m2v file to mplex the audio to.
How do I know how long to make the blank video?
what can I do to make the video low bitrate?
This is just to get around the constant switching out of the CDs in the car. The DVD player still plays the audio while I am driving just not the video.
thanks