pennmw83 wrote:
I honestly doubt your cable company was pushing that much bandwidth down the pipe. Most cable companys push something in the range of like 6-9MB not 14-17MB, since regualtions allow only up to 19Mb/s. That is what you get for the crap cable companies for trying to squeeze 3 HD channels (as sub channels) onto one actual channel.
OK, well, let's make sure we know the exact numbers and actual specifications of what's going on with U-Verse and cable providers as far as HD bitrate. U-Verse is sending H.264 (also called MPEG-4/AVC) video at 1920x1080i/59.94 and 1280x760p/59.94, both at anywhere from 5.5-6.5 Mbps depending on the channel. This is pretty aggressive compression for HD. I personally am quite amazed it works as well as it does at that bitrate. Over-The-Air (OTA) broadcasts are allocated 19.3 Mbps per channel slot. They typically have 2-3 subchannels, with the main subchannel (x.1) carrying the HD feed, and the other subchannels (x.2, x.3) carrying SD feeds. Normally, for the main HD channel, they are broadcasting MPEG-2 video at 1920x1080i/59.94 or 1280x720p/59.94 at around 14 Mbps. Digital cable TV sends channels in what's called a QAM slot. A single QAM slot is a digital transport mechanism that spans 2 analog channels on the cable. The QAM slot carries data at 38.6 Mbps. Cable companies used to send the subscriber 2 HD channels in one QAM slot, giving up to around 19 Mbps MPEG-2 for each channel. Most cable companies, to save bandwidth on their cable, are now squeezing 3 HD channels into 1 QAM slot, for about 12 Mbps per channel. 1920x1080i/59.94 MPEG-2 starts to have slightly visible artifacts below about 16 Mbps, and quite noticable artifacting at around 12 Mbps. You can't directly compare MPEG-2 vs. H.264 in terms of bitrate, since the artifacting they produce is distinctly different. But a general rule of thumb is that H.264 can usually provide a picture indistiguishable from MPEG-2 at half the MPEG-2 bitrate. There is no doubt about it, these bitrates are low for HD. Here's a comparison of bitrates and quality on several HD video sources: Cable: 1920x1080i/59.94 @ 12 Mbps MPEG-2 (bad) U-Verse: 1920x1080i/59.94 @ 6 Mbps H.264 (not good  ) OTA: 1920x1080i/59.94 @ 15 Mbps MPEG-2 (decent) AVCHD: 1920x1080p/24 @ 10 Mbps H.264 (nice) Blu-Ray: 1920x1080p/24 @ 25 Mbps H.264 (pristine) U-Verse's 6 Mbps H.264 would seem to be equivalent to Cable's 12 Mbps MPEG-2 by the thumbrule above, but H.264's artifacts are less objectionable than MPEG-2. MPEG-2 starts to just break into the (very) noticeable macroblocks when starved for bitrate, but H.264 hides them much better. We get the shifting background, the color banding, and the inaccurate luminance and color in dark picture areas, but we don't get the macroblocks. OTA has the capacity to look very good if there were no subchannels, but more and more subchannels are starting to appear as we get closer to the digital change-over date, robbing the main HD feed of bitrate. AVCHD is a disc format that allows Blu-Ray compatible playback structures on DVD media. Many people use this format to make backups of their Blu-Ray discs. I've made a few and they look great. Also, to the person who described U-Verse as "HD Lite": "HD Lite" actually has a very specific meaning. In the early days of HD broadcasting, DirecTV was broadcasting around 4-5 HD channels using MPEG-2 (all DirecTV HD channels are now H.264). These MPEG-2 HD channels were limited to about 10 Mbps by DirecTV's system, which was too low to provide anything close to a decent-looking picture. What DirecTV did was intentionally downsample the resolution of the broadcast from 1920x1080i/59.94 to 1440x1080i/59.94. This was fully 1/3 fewer pixels to encode, which reduced the bitrate requirements by 1/3. It allowed 10 Mbps MPEG-2 to look just as good as 14 Mbps MPEG-2. It was this process and type of HD that was colloquially labeled "HD Lite". No broadcaster is doing this anymore, so there is no more "HD Lite" by proper use of the term. Also, of course, don't forget the audio that is associated with these feeds. U-Verse, cable, satellite, and OTA are all using 384 kbps Dolby Digital for 5.1 sound. Dolby Digital is a pretty good codec, but 384 kbps is a pretty low for 5.1. Standard DVD uses 448 kbps. AVCHD and Blu-Ray use 640 kbps DD for standard audio, and have various higher end audio codecs that sound phenomenal, all the way up to lossless compressed and uncompressed audio. All in all, the HD quality we're getting from any provider, be it U-Verse, satellite, OTA, or cable is pretty low-end, in my book. Until everything looks like Blu-Ray or better, I won't be satisfied. But at the same time, I'm not going to complain, because truthfully, the bandwidth isn't there yet. To carry a Blu-Ray feed to your house you need 30 Mbps per channel. That's not going to happen for a while, so no sense in complaining. Message Edited by SomeJoe7777 on 01-05-2009 10:35 PM
- SomeJoe7777
What's your art?
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