I installed the Myth-Archive package to be able to backup any shows that I had recorded that I may want to keep. However, it did not work first time, so I gave up with it. It would probably have been better ti fix that, but I could not be bothered, so I have tried a different approach. First I was going to simply query the database and find out which mpeg file is associated with which program, and then manually do the archiving.
What I noticed is that some of the files have a .nuv file extension. This is not very helpful, so I did a quick Google, and found Nuvexport. This looks like a great little program. When it is run, a number of options are presented to you, and it is possible to select a number of programs to process. Options are given for what format it is to be saved in. Once I have extracted the files from Mythtv with this utility, I will use some of these recipes to create some DVD archives.
Update: Nuvexport refused to recognise the aspect ratio. Instead, I am using mythtranscode directly to export the file from Mythtv. It may not be as intuitive, but it works.