Screen capture from TV shows jumpy

[nodnyl]

I am trying to use Debut, latest version, to capture a PBS show that I missed. From PBS.ORG, I stream the show full screen, and have made sure my format is NTSC. However, I've tried avi, mpg, and other options, but the result is very jumpy as if the frame rate is way off. The sound is OK and is synced - best I can tell. The result is not watchable. Are the TV websites sending the old shows in a format that Debut can't capture, or is there a combination that will work?

Thanks.