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Discussion Starter · #1 ·
I have been looking at raw HDTV transport streams from HBO and OTA CBS. I was surprised to find that HBO is giving us 1280 x 1088 HDTV for things like "The Sopranos" and "Scooby Doo".


OTA CBS is giving us 1920 x 1080 for things like CSI.


I wonder what exactly HD OTA Fox and ABC are. What is Showtime giving us? 1920 x 1080 is what I have heard that Showtime uses.


This brings up a few interesting issues:


1) HBOs "lesser" HD looks as good to me as OTA CBS

2) the HBO format may be easier to compress onto say a DVD

3) if I didn't do some geeky peeking with a Hex Editor I would not have known this at all


Equipment used for this investigation:


1) 169time recording solution with DTC-100 and JVC 30K deck


2) Powerbook with DVHSCap, VLC and HexEdit


Sorry if someone has already mentioned this.
 

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bwooster,


This has been mentioned before. From HBO, the source is 1920x1080. DirecTV is re-encoding and reducing resolution to 1280x1088 so as to limit the maximum bit rate required - likely so it will "play nice" with Hdnet on the same transponder, using stat mux.


Many people have not been able to tell a difference with their displays. Those who do report a difference generally characterize it as subtle. Personally, I find this trend disappointing, particularly as display technologies will only improve (i.e. 1920x1080p with 3/2 pull down) in the next few years to better resolve the full 1080i signal.
 

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What is your display. I think most displays can't give you anything close to 1920 horizontal. Direct Views are around 1000, 7'' CRT RPTVs do like 1200. I think 9" CRT's can do 1920. Likewise, for fixed pixel displays you got to double check what the actual horizontal resolution is. But, I'm sure you already new that.


CKNA

Why wouldn't you get 1920x1080 on cable?
 

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Maybe a niche product like Voom will broadcast full resolution HD in all it's glory.


Lon
 

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I don't like this trend that is happening to HD. It's like when digital satellite first started, everything was less compressed and looked great and slowly more and more compression was added cramming more and more stations into the same bandwidth until everything looked like it was running off my VCR.

I hope the same thing doesn't happen to HD so 5 years from now all HD looks like DVD quality.
 

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Discussion Starter · #7 ·
My display is a JVC G150cl projector so it is 1365 x 1024.


>> you need to switch to Dish Network or get a BUD.


What is a BUD? Is Dish Network providing 1920 x 1080 HBO?


I might switch since I am recording things like Sopranos in HD. I'd like to record 1920 x 0180.


Will Directv ever give us true 1920 x 1080?
 

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Cable gives just passes the signal (as far as I know that's what Comcast does) so you get full res if they do. This isn't an HD trend, it's a Direct tv trend to juggle bandwidth until they find(obtain) more bandwidth.
 

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Quote:
Cable gives just passes the signal (as far as I know that's what Comcast does) so you get full res if they do. This isn't an HD trend, it's a Direct tv trend to juggle bandwidth until they find(obtain) more bandwidth.
I don't know if that's true or not. IIRC, at least one or two large cable companies have purchased or ordered the same HDTV stat mux equipment that DirecTV is now using (Comcast isn't one of them). Whether they bought the equipment just to stat mux, or also plan re-encode some channels at a lower resolution like DirecTV, I do not know.


I'm betting that the upcoming Voom satellite service will also downconvert to 1280x1080i (I don't see how else they could fit all that HDTV on 11 transponders), but we'll soon find out.
 

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I beleive BEV has decided to recompress signals however they won't admit it. I could be wrong though.
Well, we know that network channels on BEV use significantly more compression than the networks broadcast OTA in many markets. However, it is possible that the particular networks they've chosen to carry just happen to be running their HDTV feeds at lower bit rates (higher compression) to accomodate one or more subchannels.
 

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bfdtv...


Can you explain stat muxing? What is it a why does D* do it. what the advantages for them and the disadvantage for us?
 

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bham,


In simplistic terms, stat mux describes load balancing between channels. If you have only 31Mbps to work with, you can't have two 19Mbps channels. Rather than dividing the bandwidth evenly at say 15.5Mbps per channel, they can use stat mux equipment to allocate bandwidth as needed depending on the content. For example, one channel might have a sporting event and need 18.0Mbps, while the second channel drops to 13.0Mbps. Later, the second channel might be showing a nature video and increase to 16.5Mbps, while the other showing a movie drops to 14.5Mbps. Stat mux always involves additional compression; it's just a question of how much.


This generally works pretty well, since both channels don't usually show lots of intensive material or movement at the same time. Of course, when that does happen, quality can suffer. DirecTV has done their best to mate channels on each transponder that are least likely to be show bandwidth-intensive content at the same time.
 

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Statistical multiplexing is a far, far superior method of dividing a finite amount of bandwidth between 2 or more channels than simply dividing the channels into the bandwidth and fixing it at that.


Statistical multiplexing is not the evil, it is insufficient bandwidth overall.
 

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In addition to what rogo and bfdtv explained, I try to understand how it works by knowing that it is quite inefficient to reserve a full block of bandwidth for a program that rarely uses it. Most HDTV 1080ix1920 is not using the full 1920 100% but only a fraction of the time. By using the latest technology statistical multiplexing several data streams may be muxed into one output stream (2 or more VBR's to one output CBR). They can mesh nicely allowing the what in effect is sum of the parts = to more than the whole. The base bandwidth of each individual stream is much less than that required during peak moments. Therefore two data streams may be muxed sharing a portion of the total and reserving another portion for the base. Look at your hands with fingers extended. The palm of each is the base and fingers would be the rare peaks. Now clasp your hands with interlocking fingers. This is statmuxing. Normally this will preserve a higher quality for each of the data streams, even during peak requirements but should each of the individual streams begin to raise the base or in practical terms, begin to go into high motion and large picture area detail at the same time, then the process begins to break down and fail producing what we have observed on DirecTV HDTV in recent weeks, with minor picture disruptions and even blackouts on a channel. In a reserved, bandwidth segment major assets are wasted but the signal rarely suffers quality loss breakdown during peak loading assuming the reserve was big enough, but this is quite wasteful. In the case of an HDTV tp, the reserve using the old technology was the full TP with some bandwidth capacity wasted 100% of the time.


Let's say that 90% of the time multiple programs can share a portion of the TP without issues but then 5% of the time we come dangerously close to two or more streams competing for that additional space. 5% of the remaining time they actually clash and something visible occurs for that moment. The alternative would be to drop some of those signals and go back to the old way of reserving large bocks of space on the tp for those you keep.


The process allows an average amount of time that the program will be sent at full quality from it's source because at those moments in time the program's full quality is only 30 to 50% of the specification quality for the signal format, but then breaks down every so often without real warning when 2 or more programs go after the shared space as those programs begin to go into 75-80% of spec. resolution and/or begin rapid motion.


To my knowledge this process does not resample the inbound stream at a lower resolution. While there may be some periods of experimentation where they did that, ie combining resampling to lower quality plus statmuxing, the use of this technology does not require it. When you read postings that the resolution is no longer 1920 and is now 1280 the trend of lay thinking is that it has been resampled. Fact is the issue is far more complex than this oversimplification. Many parts to the process contribute or hinder the passage of the highest resolution components of an image including your final monitor you are watching.


Finally, everyone must understand and never forget that the process is an ongoing operation. DirecTV does not just set it and forget it. They have a team of engineers constantly working the throttles as well as other teams that try new technology so what ever is believed today as what is, tomorrow or 2 hours from now may be juggled quite differently. To claim that DirecTV's HBO is worse than DishNetwork as a fixed fact is just plain ignorant. However, to say that one has a history of looking softer on certain channels than the other most of the time may be an accurate assessment of technical policy by the provider.
 

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The stat muxing and down sampling are two different choices that can be used independently or together.


But it would make a lot of sense to down sample to only a 1280 (or 1440) width if D* needed the bandwidth and had already come to the conclusion that most of their source material did not have any more effective horizontal detail than 1280 anyway for various reasons.


While not a D* customer I will still stand by the claim that I would rather have a quality 1280 than a bit starved 1920 full of macro blocks and mosquito noise.


- Tom
 

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Quote:
Originally posted by trbarry
While not a D* customer I will still stand by the claim that I would rather have a quality 1280 than a bit starved 1920 full of macro blocks and mosquito noise.
In a perfect world, I might agree ... but in our world when you give an inch, they take a mile.


HDC
 

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Quote:
Originally posted by Don Landis
To claim that DirecTV's HBO is worse than DishNetwork as a fixed fact is just plain ignorant. However, to say that one has a history of looking softer on certain channels than the other most of the time may be an accurate assessment of technical policy by the provider.
I agree with Don's assessment.



It's also my opinion that Dish's SD channels are (and have been for awhile now) more compressed than DirecTV's, which may be an indicator of what we can expect in the future for HDTV channels. Or not.
 

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Rate shaping is another bandwidth-conserving technique being used by the cable industry. Perhaps someone knows of DBS use. With rate shaping, as this Broadcast Engineering article outlines, null bits are stripped away and 'requantization' takes place without actually decoding/recoding the MPEG-2. The MPEG-hardware folks authoring the piece are a little vague whether HD resolution is affected by rate shaping. Perhaps someone into MPEG hardware/software could elaborate? Terayon touts its newest rate-shaping hardware being used by New York's Time Warner Cable , at least for SDTV and possibly HD, too.


Statistical multiplexing, not surprisingly, seems to come in different flavors, and you might expect newer hardware to do a better job. That's the message, at least, from the Scientific Atlanta folks that authored this pdf paper . They point out the newest statmuxing hardware can better avoid conflicts between programs sharing the same bandwidth by delaying one or more of the programs when real-time analysis shows conflicts are possible. -- John
 

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Quote:
To claim that DirecTV's HBO is worse than DishNetwork as a fixed fact is just plain ignorant
This thread is about HBO not having full resolution on D*. It is fact that D* is lowering it. E* and many cable companies do not do this and pass it with full resolution. That is what I was referring to.


Quote:
It's also my opinion that Dish's SD channels are (and have been for awhile now) more compressed than DirecTV's, which may be an indicator of what we can expect in the future for HDTV channels. Or not.
E* SD channels look softer but on D* I can see a lot more pixelation. It depends which one is more distracting to you.
 
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