If you're encoding a 1 hour 56 min film across 2 SL DVDs you won't need to do multipass encoding just 1 pass constant bitrate, because of DVD maximum bitrate limitations you won't fill the entire two discs;
1h 56m video with 1536kbps audio, video encode bitrate is a fixed 8227kbps
1h 56m video with 448kbps audio, video encode bitrate is a fixed 9341kbps
the video+audio will end up being 8,327mb (8.13gb)