Are you getting what you pay for?

[Dr Mordrid]

In the past I've noted that satellite/cable providers often broadcast at less than a full 720x480 or 704x480 frame size to save bandwidth.

Recently I ran across some verification of this in the form of the format used by The Dish Network. Basically, The Dish Network is using 2/3-D1. This is the same 480x480 resolution used for NTSC Super VideoCD's.

The specifics of this are also interesing. Assuming that they are using a 4:2:2 colorspace this would mean YUV horizontal resolutions of;

Y channel: 480
U channel: 240
V channel: 240

Dr. Mordrid

[wkulecz]

My local Time-Warner "Digital Cable" system could be a poster boy for poor quality mpeg encoding. MTV2 is consistantly between VCD and SVCD in quality assuming you're not using TMPGEnc :-(

--wally.

[paulw]

What bit rate are they using Doc?? 4 - 5 Megbit??

[Dr Mordrid]

Actually a bit less than 5 Mb/s, depending on the channel and type of content. Each transponder has an available bitrate capacity of ~28 Mb/s on which several channels will be multiplexed.

ex: an audio "listening" channel might get 64-128 Kb/s while each of several video channels might get 3-4.5 Mb/s

A channels bitrate is assigned by content. In the case of video a sports, action flick and other high motion content might get 4-4.5 Mb/s while a talking head program might well only get 3 Mb/s.

This system is called "Time Division Multiplexing", or TDM, and has been used for quite some time. The problem is that sometimes a program allocated a small bandwidth might well have an action scene that trips up the system. This would likely result in the breaking up of the stream into a pixelized mess.

A newer system (as in just a few months old and not used everywhere) is "Statistical Multiplexing", or StatMux. In StatMux each channels encoder "talks" to the others on the same transponder to dynamically allocate the bandwith resources in a more efficient manner.

Dr. Mordrid