Hardware Encoder Support
Most cx88-based cards are capable of receiving analog video and audio signals as raw bit streams. Some of these cards, particularly Hauppauge models, have built-in hardware MPEG encoders that allow the cx88 analog and MPEG TS functions to cooperate to deliver the analog stream as a more compact and versatile MPEG stream. While this can be done easily enough in software on basically any machine built within the last 4-5 years, support for these encoders in the cx88 driver might be a nice-to-have feature. A prime candidate would be the CX23417 encoder, which seems to be in widespread use. Much of the of the control logic for this could possibly be implemented in userspace.
Of course the real CPU hog comes when you do things the other way around; namely, software decoding of an HDTV MPEG transport stream into raw pixels. Again, modern CPUs can handle this fairly easily, and in some cases this burden can be taken up in part by the GPU. Hardware decoders are relatively rare--a raw 1080i stream, even in the most compressed pixel format, would saturate the PCI bus. At least a x2 PCIe 1.0 or x1 PCIe 2.0 link would be needed for decent bandwidth headroom, so these suckers are an expensive proposition.