I think I may be out of date here, Bibbles. I was trying to remember the size of the files when I used to record TV onto a Hard Disk. Perhaps the Mp4 format is more gigabyte -hungry.
Doing a bit of Googling, it seems that with phone cards and the like, 1GB might only be around 20mins. It must be the format.
Anyway, no help at all I'm afraid. All I can suggest is file compression software that I mentioned above. I used to use DVDShrink a lot, but I think it's been discontinued. There are newer alternatives though, I'm sure.