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[ NNSquad ] FW: [IP] Comcast HD Quality Reduction: Details, Screenshots - AVS Forum


From: Bob Frankston [mailto:bob37-2@bobf.frankston.com]
Sent: Wednesday, April 02, 2008 11:36
To: 'dave@farber.net'
Subject: RE: [IP] Comcast HD Quality Reduction: Details, Screenshots - AVS Forum


It would be interesting to compare these examples with streaming HD over IP on a high end PC. I was impressed by how good HD Lost looked view from http://www.ABC.com on my Quad Extreme/8800GTX in a 2500/1650 screen but one would have to do a detailed analysis. It’s only 2Mbps which would be far less than any of the examples but I’m presuming that the video stream was crunched ahead of time whereas real time compression would be far more problematic.


In the examples given it would be interesting to compare the same content at HBO compression vs say AETV – is the difference due to processing or reduced “quality”.


It would also be interesting to compare FiOS VoD with FiOS broadcast. The former is over IP in what is supposedly a 20Mbps band for multiple HD streams. That would seem to require more compression that Comcast is doing. As an aside, the Mocalliance claims that IP isn’t for video which is why they us RG-6 within the home and FiOS requires the use of the Actiontec router (or the mysterious NIM-100). It’s not just that all of this is rife with just-so stories for customers – these stories are necessary to maintain their own illusions that they are necessary – just like with IMS from the people who have a desperate need to believe in IMS.


I put quality in quotes because the simple metrics of bits aren’t necessary the right ones. I remember when Bose gave a talk about why linear measurements are not as important as psychoacoustic measurements. Remember that he was a professor at MIT before he took a side job selling speakers. On the other hand if you pay for a 60” screen it’s about bragging rights not just perception.


As with MP3 extreme compression has value in enabling new opportunities but at some point there is sufficient capacity and other metrics become more important. In the case of MP3 it hangs on because it has become the generic term for compression even if it’s still a trademark – a good reason why such trademarks should lose their protection as people confuse a particular product with a concept.


As with the Bit Torrent affair Comcast is in a bind – they have to squeeze as much as they can out of the existing facilities because building new facilities is not only expensive but increased capacity would make it far easier to bypass. And as I pointed out long ago, upgrading the set top boxes is also pointless since the technology is moving too fast on generic platforms. Again, it’s also about perception – Verizon says that fiber is magic so Comcast is now advertising that they too have fiber somewhere in their network. Shiny glass.


This all makes it hard for me to understand why people argue that telecom is forever because they control the transport when it’s increasingly obvious that it’s becoming a burden rather than an asset.


From: David Farber [mailto:dave@farber.net]
Sent: Wednesday, April 02, 2008 08:40
To: ip
Subject: [IP] Comcast HD Quality Reduction: Details, Screenshots - AVS Forum





Comcast HD Quality Reduction: Details, Screenshots

Last updated: March 24, 2008

Until recently, most Comcast systems passed all HD as is from the content provider, without any added compression or quality reduction. In response to competitive pressures from DirecTV and Verizon FiOS, Comcast recently decided to sacrifice some quality to improve quantity. By early April, most Comcast systems will recompress and degrade their HD, much like DirecTV and Dish Network do on their MPEG-2 channels. This creates room for new HD channels without the need to eliminate a significant number of analog channels.

Previously, Comcast allocated a maximum of two HD channels per 38.8Mbps QAM, so each channel had the full 19.4Mbps available if needed. Now, with the addition of new channels, Comcast is squeezing three HD channels into each 38.8Mbps QAM. Furthermore, some existing QAMs with two HD channels are being recompressed in preparation for new channel additions.

But what does that mean? How much difference is there, really?

To find out, I decided to compare the quality of the same programs on Comcast and Verizon FiOS. I recorded the same program from the same channel, at the same time, on both Comcast and Verizon FiOS in N. VA. I compared the size and bitrate of each MPEG-2 recording, as well as the subjective quality with video.

Note when I tested channels late last year, there were no differences between the two providers on HD. Any differences are new.


picts etc follows djf