Basically, you have three choices:
- A capture card that has a hardware encoder. This will grab and encode video on the fly without bothering the CPU much. These are expensive and may not compress to the format you want. Then again, the quality is excellent and you don't need a very powerful PC.
- A lousy capture card and a powerful CPU. The capture card will throw all the data at your CPU that has to compress it on the fly. Depending on your disk speed and CPU power, your compression choices are limited.
- A lousy capture card and lots of fast disk space (preferably RAID). The capture card will not compress anything, nor will your CPU. The raw video is dumped on the disk and you can compress and edit it later. You need a disk that can keep up with the datastream.