About a month ago in Greece most of the TV Channels changed their broadcast type to Digital (DVB-T). I was waiting for this change for quite some time now since i have my Media Center PC connected at a Projector (720p).
On the date of the change i turned my Antenna and started to search for the Digital channels from my Windows Vista installation only to see that my TV Tuner found all the channels, the TV Guide was dispayed correcly but no sound or image was displayed in any of the channels (some had only sound).
After upgrading the system with the latest windows updates and also installed all the codecs i could think of I started thinking that the problem was with my TV Tuner (WinTV-HVR-1300). After quite some time searching in forums and blogs and even though most of the posts were suggesting that i need to buy a new more recent TV Tuner I found someone that was suggesting updating to Windows 7.
After doing that everything worked as a charm. As it turns out Earlier Windows (up to Windows 7) do not support MPEG4 and H.264 for live TV. And there is nothing you can do that would work correcly other than upgrading your system.
So if you want to be able to see DVB-T Channels with MPEG4 and H.264 Encoding on your Media Center PC you have to upgrade to Windows 7!