Originally Posted by sgbroimp
I hear ya'. As I recall one node is about 38; when they put two HD stations on one, we get about 19 which yields a nice picture. When they cram in 3, we get about 12 and change and that can bring a pretty mushy picture. An on the 550 and 650 systems, they are very "node-challenged", right?
Yeah mean one channel or one QAM? A node is where the fiber converts to coax for the "last mile" (which could be anywhere from several miles in a rural area to a part of a building in NYC). They are bandwidth challenged, because there are not enough QAMs to fit everything in. However, you need to separate picture quality from channel lineup. Comcast compresses their channels for the whole market or region, so customers in Madison (Branford plant), which is an 860mhz Moto system rebuilt in 2011 have the same poor picture quality on many of the local channels. However, on channels that just don't fit on the 625mhz and 650mhz systems, like ESPNUHD and AJAM, the picture quality is actually quite excellent. Basically, the bandwidth constrained systems are the lowest common denominator, and are pulling the picture quality down for everyone, and the high-bandwidth systems have enough room that the additional channels they get are running at rather high bitrates. A few channels run at high bitrates everywhere, like HBO, ESPN/ESPN2, and RedZone, likely because of contracts with the providers of those channels that prohibit Comcast from compressing them beyond a certain point.
Then they went to a new low recently. They significantly improved their compression in the past 2-3 years, and have gotten the tri-muxed channels to look pretty darn decent at around 12mbps, which is kind of a scary thought. However, that apparently wasn't good enough, so now they have a handful of channels running at 8-10mbps. This is a new and unprecedented low in HD picture quality, and it means that they are either quad-muxing HD channels, or they are running tri-muxed HD channels with a couple of SDs thrown in on the same QAM.
The other challenge they have is that out of the 200 or so HD channels that are out there, and are available on U-Verse, FIOS, and TWC (TWC through the use of SDV), Comcast is only running around 120, even on their high-bandwidth systems, so there is still a lot of relatively specialized channels missing in HD. They do have some bandwidth left on their 860mhz systems, and they might be able to get upwards of 200 HDs on there if they really crammed them, likely with at least the upper tier stuff in H.264. However, if gigabit internet or UHD channels are going to be a reality, the math doesn't work on for current purely linear systems, even at 860mhz, which is about the practical upper limit of the bandwidth of a cable system (Cox runs a number of 1ghz systems, but they are a complete PITA to keep running, and have all sorts of problems with stuff above ~870mhz in the "nosebleed" spectrum). In order to offer a top-tier HD lineup, UHD channels, and gigabit internet, they are going to have to employ some combination of the god-awful SDV, as well as the excellent H.264. My sense is that they could probably keep the core SD lineup and a core lineup of ~70 HD channels fully linear in MPEG-2 and improve their quality a bit, and then have SDV using H.264 for the remaining ~130 HDs and oddball SD channels, along with the existing D3 and D3.1 gigabit internet deployments, although even that is a really, really tight fit on an 860mhz system.