The lowest quality channels (which will form the majority) all use a similar profile of 544x576 @ 2Mbps MPEG-2 with 128kbps MP2 audio. That's about 1/3 of a typical DVD. If it's DVB-S2 then it's the same but with more efficient codecs and the video bandwidth is a bit less (down to 1Mbps in some cases). You can just about squeeze 4-5 of these channels into the bandwidth of one HD channel. They're great for filler channels to make Sky packages more attractive.