Digital signals are recorded in the same format they are received in. In other words, if you're recording an HD clear cable or over-the-air ATSC channel then the recording will be in HD. Those recordings have a *.ts (transport stream) extension. The actual video format of the recording (MPEG, MPEG2, h.264 etc.) is determined by the broadcast format.
Analog signals (FM radio, the few remaining analog cable channels) are converted by your tuner from analog to digital so that the PC can store them. The quality of the recording is determined by the settings described here: http://wiki.team-mediaportal.com/1_...n/02_TV_Servers/7_Scan_Analog#Quality_Control
Those recordings also have a *.ts extension. The video format of the recording will be MPEG or MPEG2.