What format will the recording be on the USB I would like it to be MP4 as I will be using an IMac for archiving to.
Mpeg2 Video in a .m2TS container, but with a transport stream container extension, Audio Mpeg 1 layer 2 (MP2). Basically as broadcast, a PVR streams the digital data as is, but may encrypt it as it saves the data stream to hard disk.
Will I be able to convert it to MP4 for playing in iTunes
No experience with iTunes, mpeg2 is a very common codec, used on DVD’s for instance so would be surprised if you can’t use as is. You may have to losslessly change the contsainer.