CDR's are marked, for example, 80 min and 700meg. Thats 80 min or Music or VCD movie or 700meg of data. But if I make an XVCD I can get 120min on the CDR but file size would be 800meg or if I make an SVCD I would normally only get 45 to 50 min on the same CD but file size would be 800meg. Confussed, then your not alone.
The same sort of thing applies to a DVDR. At a bitrate of approx 5000 ( a common DVD) you can get 120min on a DVDR but at 2500 bitrate you can get approx 240min onto the same DVDR. Lower the bitrate even further, same with the audio and reduce the frame size of the picture and you can get 8hr+ of movie. It might be utter crao quality but it will fit.
At VCD specifications you can get about 430 minitue (just over 7hrs) of movie onto a DVDR.
The whole thing is as celtic_druid said, the min printed on it is of little concern. The only thing that counts is it size in gigaBytes, and they cant even get that right. They are all labelled at 4.7GB bit you can only fit 4.37gb onto them. Same with Hard Drives, I wish I could get 80meg available on an 80meg HD.