Thanks guys for your quick replies!
I think this has to do with blocking fragmented packets, can you check the firewall settings, Attack Detection Settings, Misc, untick "Block fragmented ip datagrams".
I tried this but it seems that the problem is elsewhere, I made some more investigations on the issue and it seems that this problem is not solely related to Comodo.
The other night I watched a movie and it was skipping like crazy, and disabling Comodo fixed the problem then. But now yesterday most channels worked just fine without any skipping. Then I started recording one channel and watch another simultaneously, and it started to skip a little about once or twice a minute or so. It's just a small glitch and does not affect the audio, only the image, tiny but noticeable. But now even disabling comodo did not solve the problem, so there has to be something else causing problems as well... There's no spikes in the CPU usage, load stays below 20%, memory usage 40% or so. Dual core processor and dual receiver terrestial TV card (Terratec 2400i).
This is really weird, since the other day shutting down Comodo solved the stuttering, but now it doesn't. I'll have to do some more research and experiments, hopefully something will help. It might also be a data transfer related problem, maybe also related to the WLAN card/drivers, who knows.
Anyway, thanks again guys for your help.