Local Channel Picture Quality

Question

I've noticed that the picture quality on the local channels (ABC, CBS, FOX, etc.) isn't quite as good as ESPN for example.  I see it mostly when watching football.  Looks like artifacts or a little grainy during fast motion whether it's in the game or the graphics.  Stills or shots that don't have too much motion look great.  I have an old tube TV and just standard definition.  Football on ESPN looks awesome, crisp and clear even during fast motion.  Is this normal with the local feeds?  What causes that?  It's not a huge difference and my wife can't tell, but there is a difference.  Thanks.

KenAF · Accepted Answer

@BrianC wrote:I've noticed that the picture quality on the local channels (ABC, CBS, FOX, etc.) isn't quite as good as ESPN for example.  I see it mostly when watching football.  Looks like artifacts or a little grainy during fast motion whether it's in the game or the graphics.  Stills or shots that don't have too much motion look great.  I have an old tube TV and just standard definition.  Football on ESPN looks awesome, crisp and clear even during fast motion.  Is this normal with the local feeds?  What causes that?  It's not a huge difference and my wife can't tell, but there is a difference.  Thanks.

Motion requires more bandwidth than static imagery.  The greater the amount of motion, the greater the bandwidth required to maintain a stable, detailed image.   During intense motion and/or image transitions where the required bandwidth exceeds the available bandwidth, you'll see compression artifacts and blurred images.  This is more obvious on some channels than others, because some channels devote more bandwidth to their HD feed than others.  ESPN allocates over 18Mbps to its HD channels, which is about as high as you'll find.

Verizon passes local channels as is, but outside of FOX (where quality is about the same everywhere), quality varies by market.  Each local affiliate has 19.4Mbps to split between their HD channel and any other feeds they want to offer (carried by Verizon in the 450-499 range).   Some local affiliates devote 15-16Mbps to their HD feed and 3-4Mbps to a separate SD channel.  Other local affiliates devote 10-11Mbps to their HD feed and the remaining 8-9Mbps to several SD channels for weather, traffic, local news, etc.  The more bandwidth an affiliate devotes to their HD feed, the better the quality of the picture (i.e. fewer artifacts and less blurring during motion).

The same basic principles apply to SD channels, too.