HBO Framerate

[era]

I've now had HDTV via Time Warner cable here in Greensboro NC for a couple of weeks and I'm pretty happy with it, but there's one thing...

The quality of the HDTV Demo channel (Public Television travelogues) is excellent--smooth pans, ultra-sharp definition of detail. Quite what I was hoping for.

But.........the downside is the two movie channels....

The HBO movies almost always stutter or jitter during a pan--it seems as if the frame rate is about one third (10 per second) what it should be, so the image stammers across the screen like ABS braking does with a car. Nobody else in my house seems to notice it, so perhaps this is one of the little "compromises" that they're making during compression. Also, the images are always softer, less sharp than the Demo channel. Why is this?

I'm not mentioning the Showtime HDTV channels because they are nearly always unwatchable--wrong aspect ratio for my widescreen TV and generally fuzzy. They are listed as "upconverted" which probably means degraded in some way.

Thanks for any answers to this mystery...

Richard

[kevinw]

The demo channel is more than likely shot with a HD camera. The movies are shot on film then converted to Hd.

[era]

Thanks for your reply. I'm sure you're right, but are you saying that converting movies to HDTV must result in a low frame rate? Movies don't suffer from that jerky, 12-frames-per-minute panning that I'm seeing.

Why would it be necessary when converting a movie to reduce frame rate and cause that jerking?

[RickNeff]

No, I think he's just explaining the "softness" of the picture. The framerate issue is most likely due to either the source coming in to your local Time-Warner or their transmission. I haven't seen what you've described on HBO HD with my TWC cable system.

[era]

I also notice the low frame rate jitter on many DVD's as well. It's most obvious during a pan--when the entire picture must be redrawn many times per second. I think this simply chokes compression schemes and forces them to skip two out of three frames during the pan, thereby reducing the frame rate to 10 or lower (when it should be in the high 20's for a smooth pan). If a car speeds past in a movie, the compression can handle the static background with only a small part (the car) that must be redrawn. However, when the entire picture is in motion (panning) the frame rate takes a dive and looks pretty jumpy and nasty. That's my best guess about what's happening