As a newbie, I apologize if this question has been asked many times before, but here goes. I've done a little bit of editing and have successfully burned a few dvds. However, I don't seem to be able to get as much on a single dvd as you get on a commercial copy from the rental store. For example I recently had a 1-1/2 hour program that woudl not fit. Why is that?
Doing the math, you would have to transcode your video at about 5.188 Mb/sec VBR to get 90 minutes to fit with PCM audio.
Use the Guy Graphics Bitrate Calculator to figure the bitrates yourself. For PCM audio, use 1600 kb/sec. If your DVD authoring package can convert the audio to AC-3 Dolby Digital, you can use 192 for your audio rate to yield a video rate of 6.596 Mb/sec.