http://store.bluecherry.net/bluecherry-bc-h16480a-16-port-video-16-port-audio-h.264-pcie-hardware-compression-capture-card.html
It captures up to 4 composite-video inputs at 704x480 at 30000/1001 fps, 16 inputs at 704x480 at 7500/1001 fps, or 16 inputs at 320x240 at 30000/1001 fps. It also captures mono audio on each input, if you need it. Bluecherry has its own Linux-based DVR software (go here for more information), or you can just grab their V4L2 driver from GitHub and roll your own. (I think it's also supposed to work with ZoneMinder, but not in H.264 mode.)
(Click any of the images to enlarge.)
The card comes with video and audio breakout cables. The video breakout cable plugs directly into the card; the audio breakout cable plugs into the bracket connector, which plugs into a connector on the card.
This card needs a Linux PC with a PCIe 1x slot. Windows drivers are not available, at least not from Bluecherry. It uses a SoftLogic Solo6110 hardware H.264 compression chip, as you can see from the pictures above.
They sell new for about $300. If I could get $240 (or the equivalent in BTC at time of purchase...a hair over BTC20 as I post this), that'd be high-speed. I'm also open to trade: my hashrate is pretty pathetic right now, so if you'd like to put some security cameras on your mining rig, home, etc., maybe we could trade my capture card for a couple of Radeon 5850s or 5830s. This would be my first sale or trade here, but my eBay feedback is flawless. I'm OK with escrow.
If you're interested, I can include a tarball or (maybe) a Subversion dump of the software I was working on. I had it capturing on four inputs at full resolution and framerate, writing raw H.264 video and index files to a directory, and deleting old files as necessary. I hadn't gotten around to writing a viewer, but you can concatenate the files and write them to .mkv or .m4v files with standard utilities for those purposes.