Here's more information about my setup.
CPU: Intel Core i3-3220
OS: Ubuntu 12.04 LTS
Zoneminder: 1.24 (I think. Might be 1.25.)
bttv module options: card=77,77,77,77 (per manufacturer recommendation)
Card model: PV-155
Card URL: http://store.bluecherry.net/PV-155-16
Card interface: PCI
bt878a chips: 4
Inputs supported: 16
Inputs in use: 13
Color mode: YUV422p
Captures per frame: 1
Troubleshooting steps performed:
- Setting captures per frame to 2 decreases the artifacts somewhat.
- Setting captures per frame to 3 almost eliminates the artifacts. At this setting I see them perhaps every four seconds or so.
- Running memtest86 overnight did not turn up any errors.
- Replacing the PV-155 card with a spare of exactly the same model did not fix the problem.
- Applying heat sinks to the bt878a chips did not fix the problem.
- Moving the PV-155 card to a different PCI slot did not fix the problem.
640x480 pixels per frame * 2 bytes per pixel * 2.5 frames per second * 13 inputs = 19968000 bytes per second = approx 20MB/sec. My standard 32-bit, 33MHz PCI bus should be capable of transporting 133MB/sec, and the machine isn't doing anything other than being a zoneminder server.
Any ideas about what might be causing this problem?