Re: [H] HDTV Math
You know Comcast recompresses, right? -Original Message- From: hardware-boun...@hardwaregroup.com [mailto:hardware-boun...@hardwaregroup.com] On Behalf Of James Maki Sent: Wednesday, April 08, 2009 1:36 AM To: hardware@hardwaregroup.com Subject: [H] HDTV Math I discovered something this week and am trying to understand its ramifications. I noticed lots of pixelation and motion blur the last two weeks of Heroes. NBC broadcasts at 1080i for HDTV. I checked the statistics for the show I recorded via HD Homerun tuners using Comcast cable, and NBC is averaging about 4.8 GB per hour for a 1080i show. I thought is a bit low but was even more surprised when I checked out shows on the other broadcast networks.
Re: [H] HDTV Math
If you looked at satellite HD broadcasts I would suspect you would find even worse bitrates among several of the HD stations. It all comes down to bandwidth - the cable satellite operators have limited bandwidth and are trying to cram as many stations in as possible, and in many case this means highly compressing some stations. Usually they try to make sure that HD signals where it is most likely to be noticed (Discovery HD, PPV movies and live sports) get the best signal while other pseudo HD channels like History or HGTV will get re-compressed like crazy. --- Brian Weeden Technical Consultant Secure World Foundation http://www.secureworldfoundation.org +1 (514) 466-2756 Canada +1 (202) 683-8534 US On Wed, Apr 8, 2009 at 1:35 AM, James Maki jwm_maill...@comcast.net wrote: I discovered something this week and am trying to understand its ramifications. I noticed lots of pixelation and motion blur the last two weeks of Heroes. NBC broadcasts at 1080i for HDTV. I checked the statistics for the show I recorded via HD Homerun tuners using Comcast cable, and NBC is averaging about 4.8 GB per hour for a 1080i show. I thought is a bit low but was even more surprised when I checked out shows on the other broadcast networks. ABC 720p/60fps 6.3 GB NBC 1080i/29.97fps 4.8 GB CBS 1080i/29.97fps 5.6 GB PBS 720p/60fps 5.4 GB CW 1080i/29.97fps 7.9 GB FOX 720p/60fps 7.3 GB I find it strange that NBC has the lowest total file size but is broadcasting at 1080i, so I assuming (and I know the drawback of that!) it is compressed more than the other channels and am again assuming that is why I am seeing the picture degradation. Calling Comcast is a joke, so I wanted to do the math to calculate the 'bits-per-second for each case, but am not exactly sure if I am doing this correctly. It would seem that 4.8 GB/hr would calculate as: 4.8 GB/hr * 1 hr/60 min * 1 min/60 sec * 1024 MB/GB * 8 Mb/MB = 10.9 Mbps. One online source indicated that for quality 1080i you should have at least 15 Mbps. For the FOX network, the calculation would give 16.6 Mbps, far better than the 12 Mbps my online source gave for quality 720p broadcasts. I can't understand why the 720p broadcast is actually providing better throughput than the 1080i. It seems backwards (which is why I am wondering if my math is correct). I am not sure how to factor in the fps figures, if at all. If you can add some insight, it would be appreciated. Thanks, Jim Maki jwm_maill...@comcast.net
Re: [H] HDTV Math
Yes, I have read about how comcast compresses their already compressed (by the network) signals trying to cram more HD stations into less space. I am just trying to figure out why our local NBC affiliate seems to be getting compressed to a greater extent with worse results? FOX and CW give a better picture (one at 720p and the other at 1080i). I am just looking for confirmation if my calculation is correct or I am approaching the problem incorrectly. Thanks, Jim -Original Message- From: Eli Allen You know Comcast recompresses, right? -Original Message- From: James Maki I discovered something this week and am trying to understand its ramifications. I noticed lots of pixelation and motion blur the last two weeks of Heroes. NBC broadcasts at 1080i for HDTV. I checked the statistics for the show I recorded via HD Homerun tuners using Comcast cable, and NBC is averaging about 4.8 GB per hour for a 1080i show. I thought is a bit low but was even more surprised when I checked out shows on the other broadcast networks.
Re: [H] HDTV Math
Brian, I pay for HD and would like to think I get HD, but if comcast is only giving 2/3 of the bandwidth that is considered HD, I may look elsewhere. I have read that digital over the air broadcasts better than analog. I am about 30-40 miles from Seattle and Tacoma, where all the networks have broadcast towers, so am thinking of investigating an antenna. It is a shame that we have investing in a switch-over to HD only to not really be getting HD. I would rather have 100 quality stations than 600 crappy stations. But that is just me. I am sure there are people who get cable just for the soap network or game network, but not me. Anyway, I was just looking for confirmation or correction on my math. Thanks, Jim -Original Message- From: Brian Weeden If you looked at satellite HD broadcasts I would suspect you would find even worse bitrates among several of the HD stations. Brian Weeden Technical Consultant On Wed, Apr 8, 2009 at 1:35 AM, James Maki I discovered something this week and am trying to understand its ramifications. I noticed lots of pixelation and motion blur the last two weeks of Heroes. NBC is averaging about 4.8 GB per hour for a 1080i show. I thought is a bit low I am wondering if my math is correct). I am not sure how to factor in the fps figures, if at all. If you can add some insight, it would be appreciated. Thanks, Jim Maki
Re: [H] HDTV Math
Digital OTA broadcasts will be the best signal in terms of compression, no doubts about it. The only thing better is BluRay. Part of this goes back to past discussions we've had on here about whether 1080i is better than 720p. The biggest reason for the difference you are seeing is in the framerate. 720p is progressive scanned, which means that they are scanning every line of video from top to bottom. 1080i is interlaced, meaning they only scan every other line and alternate between frames. This way you get appearance of a full image for only half the bandwidth, and that shows up in your measurements. So 1080i does have more lines of resolution, but 720p is sending more frames. And for you videophiles, yes I know I greatly oversimplified the progressive/interlaced, 3/2 pulldown and fps definitions for the sake of argument. --- Brian Weeden Technical Consultant Secure World Foundation http://www.secureworldfoundation.org +1 (514) 466-2756 Canada +1 (202) 683-8534 US On Wed, Apr 8, 2009 at 12:16 PM, James Maki jwm_maill...@comcast.netwrote: Brian, I pay for HD and would like to think I get HD, but if comcast is only giving 2/3 of the bandwidth that is considered HD, I may look elsewhere. I have read that digital over the air broadcasts better than analog. I am about 30-40 miles from Seattle and Tacoma, where all the networks have broadcast towers, so am thinking of investigating an antenna. It is a shame that we have investing in a switch-over to HD only to not really be getting HD. I would rather have 100 quality stations than 600 crappy stations. But that is just me. I am sure there are people who get cable just for the soap network or game network, but not me. Anyway, I was just looking for confirmation or correction on my math. Thanks, Jim -Original Message- From: Brian Weeden If you looked at satellite HD broadcasts I would suspect you would find even worse bitrates among several of the HD stations. Brian Weeden Technical Consultant On Wed, Apr 8, 2009 at 1:35 AM, James Maki I discovered something this week and am trying to understand its ramifications. I noticed lots of pixelation and motion blur the last two weeks of Heroes. NBC is averaging about 4.8 GB per hour for a 1080i show. I thought is a bit low I am wondering if my math is correct). I am not sure how to factor in the fps figures, if at all. If you can add some insight, it would be appreciated. Thanks, Jim Maki
Re: [H] HDTV Math
No, for the most part that covers the p vs i discussion. If you read avsforums most people say that it's hardly noticeable, except in fast action sequences where the p will look better since there's more frames so it reduces tearing, i.e. the feeling the image is choppy; it basically looks a bit smoother, but some folks don't even notice it at all. But the 3/2 pulldown (really 2/3) only matters when you have movies involved at that's the telecine process; it's b/c movies are filmed at 24fps and tv (NTSC) is displayed at 30fps, and to get the two to sync, they have to add/duplicate extra frames to the movie to match up. I read about this recently b/c the new Blu-Ray player that I got, the Samsung BD-P2550 actually has a mode where it can output the movie in the normal 24fps as long as your tv accepts that, which all the av nuts say is the best way to do it (eliminating all the 2:3 issues). HTH! BINO -Original Message- From: hardware-boun...@hardwaregroup.com [mailto:hardware-boun...@hardwaregroup.com] On Behalf Of Brian Weeden Sent: Wednesday, April 08, 2009 9:27 AM To: hardware@hardwaregroup.com Subject: Re: [H] HDTV Math Digital OTA broadcasts will be the best signal in terms of compression, no doubts about it. The only thing better is BluRay. Part of this goes back to past discussions we've had on here about whether 1080i is better than 720p. The biggest reason for the difference you are seeing is in the framerate. 720p is progressive scanned, which means that they are scanning every line of video from top to bottom. 1080i is interlaced, meaning they only scan every other line and alternate between frames. This way you get appearance of a full image for only half the bandwidth, and that shows up in your measurements. So 1080i does have more lines of resolution, but 720p is sending more frames. And for you videophiles, yes I know I greatly oversimplified the progressive/interlaced, 3/2 pulldown and fps definitions for the sake of argument. --- Brian Weeden Technical Consultant Secure World Foundation http://www.secureworldfoundation.org +1 (514) 466-2756 Canada +1 (202) 683-8534 US On Wed, Apr 8, 2009 at 12:16 PM, James Maki jwm_maill...@comcast.netwrote: Brian, I pay for HD and would like to think I get HD, but if comcast is only giving 2/3 of the bandwidth that is considered HD, I may look elsewhere. I have read that digital over the air broadcasts better than analog. I am about 30-40 miles from Seattle and Tacoma, where all the networks have broadcast towers, so am thinking of investigating an antenna. It is a shame that we have investing in a switch-over to HD only to not really be getting HD. I would rather have 100 quality stations than 600 crappy stations. But that is just me. I am sure there are people who get cable just for the soap network or game network, but not me. Anyway, I was just looking for confirmation or correction on my math. Thanks, Jim -Original Message- From: Brian Weeden If you looked at satellite HD broadcasts I would suspect you would find even worse bitrates among several of the HD stations. Brian Weeden Technical Consultant On Wed, Apr 8, 2009 at 1:35 AM, James Maki I discovered something this week and am trying to understand its ramifications. I noticed lots of pixelation and motion blur the last two weeks of Heroes. NBC is averaging about 4.8 GB per hour for a 1080i show. I thought is a bit low I am wondering if my math is correct). I am not sure how to factor in the fps figures, if at all. If you can add some insight, it would be appreciated. Thanks, Jim Maki
Re: [H] New TV.
I wanted to thank everyone for all of their inputs. We have an older rear-projection 52 that I was wanting to replace. The wife was balking at the $1800-1900 prices I was wanting to get (the 52 Sony Bravia or 52 Samsung 650). She was pushing for a 46 model to save a few dollars. Anyway, I came across the SAMSUNG LN52A630 at Frys for $1500 + free shipping. It turns out the 630 has a more matte screen which will work out well with my window/TV placement. http://shop3.frys.com/product/5748772;jsessionid=tkXINGh1ff4LnXVt444JXQ**.no de3?site=sr:SEARCH:MAIN_RSLT_PG Thanks, Bobby
