[Tig] compressing cable feeds

[Bob Friesenhahn]

On Mon, 22 Jan 2007, Greg D. wrote:

> I was told by comcast a couple yrs ago that they too were passing the HD
> feeds "as is."  They did admit to compressing all the other channels to
> "fit" as many as 6-12 digital std def feeds into the bandwidth of what an
> analogue channel does/used to require.  I thought then that they were
> probably going to try to send HD as good looking as they could in the
> beginning, but then would certainly eventually compress to add more
> capacity.  I believe that is happening at Comcast now and other providers as
> they add more SD and HD channels.  To provide more, they are most certainly
> compressing more.  My 15 or so HD feeds show a lot of compression!

I think that it is really hard to do good HD compression.  Poor 
compression will be noticed quickly on major feature films. 
Real-time HD compression takes serious hardware and still does not 
obtain the possible motion estimation vectors available from the input 
image stream.  The available bandwidth of the channel can not be fully 
utilized due to fear of accidentally hitting the limit. This is reason 
why real-time sports broadcasts suffer in HD and some sports 
broadcasts look much better than others.

I notice that some HD sports broadcasts seem to use color/intensity 
compression/remapping which helps the image compress but creates a 
surreal effect (e.g. color of the grass is re-mapped).  Apparently 
they think that the viewer won't notice.

If HD material is delivered already compressed with high grade 
compression, decompressing it and then attempting to compress it again 
in real time to save bandwidth is likely to introduce major problems 
and will likely consume even more bandwidth than the original 
material.

Bob
======================================
Bob Friesenhahn
bfriesen at simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/