I would check www.dvdrhelp.com for more information. They have a free tool called a bitrate calculator where you can input the length of the movie and the audio format and it will tell you how high you can set your bitrates in order to fit your movie on one DVD. I'm looking at using AC-3 when I redo my LD conversion as it takes up a lot less space than uncompressed PCM audio and the quality is virtually identical as long as you use the right AC-3 encoder.