From what I understand, there is the standard release of Dune, and then there was a second release called 'TV Edition', which had extra footage. I've never seen it myself, but I just looked it up on Play and they have the running time as 3 hours. I think it was aired in US TV.
I think that the opening scene where the princess is reciting some of the background lasts about half an hour in this version ! It is 4:3 ratio and stereo.
I was hoping they would work some of the additional footage from that into this new SE, but it's looking doubtful now.