My current system relies on 4 channel PCI cards each based around a single Conexant BT878 chip. They advertise a rate of 30fps (frames per second) which decreases by 50% for each camera added, resulting in approximately 3.5fps if all four ports are used (these cards can be had on Ebay for $10 a piece, with shipping included).
The card acquired for the new DVR relies upon 8 separate Conexant BT878 chips and claims 240FPS (30 FPS per input), although this will need to be tested (truthfully 10-15fps would be more than adequate).
Image resolution at 640×480 is doable, although this is a problem for the computers processor not so much for the DVR card.
Increasing both the frame rate and resolution will have a significant impact on the computer (processor, memory and storage), and I’ll have to seek the most bang for my buck in these respects.
As with the existing system all but the multiplexed feed will be recorded on a “movement” detected basis, and while this will reduce (if properly configured) the storage space needed it will increase the demand on the processor and memory.
Obviously I’ll be shopping around looking at computers next.