CD & DVD dvd-r space

[SUPERTOM]

well my mate lent a dvd copy 4.7gb i made a copy of it . 2 hours but when i put it in my dvd player the film was 3 hours. so how do thay get 3 hours on a 2 hour dvd-r.is it a diffrent format or what.it would like to know because most of my filems ara over 2 hours..can someone help...