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Discussion Starter · #1 ·
I realize that the HDTV resolutions are a "standard" (1080i, 720p, etc) but I'm wondering if the compression algorithm is also included in that standard?


With wavelet based compression looking very promising (it blows away jpg for still images), it would be a shame if we were stuck having MPEG2 video streamed to us in 15 years when there will be much better algorithms available by then.


I think that MPEG2 often looks excellent, but in scenes where there is a lot of movement, the screen becomes extremly blocky. I'm guessing this is due to the available bandwidth and how the compression algorithm uses this bandwidth.


Scott
 

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Nearly all of the HDTV playback hardware has MPEG2 decoding ICs that cannot decode other compression schemes...


So - I think MPEG2 will be an integral part of HDTV for a long time...
 

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Well when they make everybody buy new set top boxes and TVs to support some encrypted standard, I guess they could advance the compression technology at that point, but I know that they won't.


[This message has been edited by Pultzar (edited 10-09-2001).]
 

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Right Pultzar, and that's what PVR meant. That's sad, really. I don't like watching digital tv (e.g. mpeg2). My 1976 indoor antenna gives me a better picture then my digital cable (no hdtv yet). Even with excellent bandwith and a perfect decoder my eyes still see it's compressed.

 

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MPEG video compression can be as harmless as the broadcaster wants it to be. It is not a compressed-or-not issue but how adequate the amount of compression is to the program requirements.


As most of the public don't care or even notice the artifacts of excessive compression, there's little incentive for the broadcasters not to extract the maximum profit out of the available bandwidth.


For manufacturers, a flawed design or implementation is always a good thing, as band-aids can be released every year to extort money out of customers willing to get the most quality. The best recent example is DVD players.


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[This message has been edited by proufo (edited 10-10-2001).]
 

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The FCC requires MPEG2 for all OTA DTV in the US, but the FCC does not require the 18 (or 36) formats specified by the ATSC.


Other forms of HDTV are not necessarily restricted to MPEG2. So wavelet-based compression could be used for satellite, cable, HD-DVD, Internet, etc.
 

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Discussion Starter · #7 ·
I think that a likely scenerio is using wavelet compression over the internet. Unfortunately, the focus will probably be toward low bandwidth low quality video (by HD standards) as opposed to HDTV quality video.
 

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With MPEG-4, I can take a DVD and compress it down to fit on a CD. Of course, the quality suffers, it's about VHS in slow speed on a bad tape quality, but that's a heck of a drop from 4+ GB to 640K.

The compression can be selected so there is a direct transfer and it looks as good as the original, but you know what the DBS companies would do with it.


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If I remember correctly, MPEG2 is a data format, not an algorithm. Decompression algorithms for MPEG2 are rather simple and unchanging, and those are what are built into all of our sets.


There are continued improvements in compression algorithms to create MPEG2 streams, and there still may be room for improvement in MPEG2 encoding, which could be upgraded.
 

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davegust wrote:
Quote:
There are continued improvements in compression algorithms to create MPEG2 streams, and there still may be room for improvement in MPEG2 encoding, which could be upgraded.
Excellent point, Dave. The quality is indeed very dependent on the MPEG2 encoder, and improvements can and are being made. A really good example of how this is possible is Sony's "minidisc" format, which uses a Sony-proprietary audio compression scheme called "ATRAC". The first version of ATRAC was, for some critical listeners, inadequate. Sony has continued to improve the compression algorithms, going through successive ATRAC "versions". The current versions sound very good, but are still playable even by the very the first Minidisc equipment ever sold.


But improvements in compression capabilities won't matter much if the carriers (cable, satellite companies) decide to accept less quality in order to squeeze more channels into their conduits.
 

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Originally posted by roman:
You'll see compression artifacts on video that isn't 'prepped' for compression. Notice the mimimal artifacts on the latest DVD videos (which use the same exact MPEG2 as DTV).
But there's a limit on this. If the bandwith is too low, the end result is crappy. DVD bitrate is much higher than even the best SD (edited) DTV standard.

Quote:
DVD manufacturers have the benefit of 'fine tuning' the encoding process to fit the video so it encodes cleanly (manually adjusting keyframes to handle multiple jump cuts and varying the encoding rate at different points, etc).
There's the capability for getting the most out of DVD compression, but that doesn't mean they always choose to do it.

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Most OTA encoders are on an automatic setting; so they're encoding live video without such benefits. It'll take a while for automatic encoders get up to the same quality level as human-supervised ones. ).
It seems that I am very sensitive to jumpiness in nodding. I recently saw a DirectTV program where the scene remained virtually static for a second or so. The character then moved his head to the side. The result was a jump from the starting point to the end of the head movement, with no in-between frames. I was with several people and nobody noticed or got annoyed.


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[This message has been edited by proufo (edited 10-10-2001).]


[This message has been edited by proufo (edited 10-10-2001).]


[This message has been edited by proufo (edited 10-10-2001).]
 

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Dvd bit rate is higher then dtv? This is news to me. HDTV is over twice the bitrate of dvd's. 480p DTV is about the same bitrate as dvd's.
 

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Discussion Starter · #13 ·
I believe that the 1080i HD DTV bitrate is about 18.2 mega bits per second (about 7.62 gigabytes per hour), which is higher than DVDs rate.
 

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You'll see compression artifacts on video that isn't 'prepped' for compression. Notice the mimimal artifacts on the latest DVD videos (which use the same exact MPEG2 as DTV).


DVD manufacturers have the benefit of 'fine tuning' the encoding process to fit the video so it encodes cleanly (manually adjusting keyframes to handle multiple jump cuts and varying the encoding rate at different points, etc).


Most OTA encoders are on an automatic setting; so they're encoding live video without such benefits. It'll take a while for automatic encoders get up to the same quality level as human-supervised ones.


On Another Note---


Moores law will continue regardless of what TV standard is chosen, but a problem is that a standard has to be made at some point. We could probrobly do wavelet compression if DTV was going to be introduced 5 years from now.... but how much longer should we be willing to wait? (Do you know how many years our current DTV system as been in the works?)


 

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The quick answer is 'No', we are not stuck with current compression technology.


MPEG2 is actually a 'decompression' standard. That is, when the decoder receives a bit stream meeting MPEG2 standards it will faithfully decode and display that bit stream as a picture. The provider of the bit stream is free to create that bit stream any way they want using any encoding algorithim tricks they can to improve the decoding process. This is why the various ATSC encoders provide vastly different picture quality at various bit rates.


DVDs work well because they are not compressed in 'real time'. Most high quality DVDs use a multi-pass compression system. The success of the compression of any single frame, or succession of frames, can be checked and the compression variables tweaked to improve the image, then recompressed.


Multi-pass 'Real Time' compression is not yet available at a reasonable cost (i.e. less than $500,000 - $1,000,000). Future compression systems could be capable of better analyzing picture content in a 'trial compression phase' and passing the results downstream to a second compression phase for better results. This would result in a much improved encoding process and a very much improved decoded picture using the very same MPEG decoder you have today.


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Quote:
...I recently saw a DirectTV program where the scene remained virtually static for a second or so. ..
DirecTV is not the same as DTV. You're at the mercy of the DSS provider's compression scheme which has different limitations as the ATSC standard. The problems you're seeing has to do with spreading the DSS spectrum too thin.


I happen to use my DTC100 for OTA only (I don't have enough free time to justify pay TV), -- every DTV station gets a 19Mb data bandwith to play with--- thus the MPEG2 issues isn't.


It's ironic because DSS providers are free to use whatever advanced encoding formats (like wavelet compression) are available, since they use their own proprietary hardware... But the problem of backwards compatibility with their current installed base is going to hinder that.



[This message has been edited by roman (edited 10-11-2001).]
 

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I don't think there is a real issue here at all. MPEG-2 is the best high data rate codec right now. MPEG-4, wavelet, and other technologies, are great but they excel at providing adequate content at minimum stream rates. For OTA HDTV the broadcasters have been granted a very fat pipe (~19 MBps) and thus MPEG-2 will do very nicely, thank you. Now if the FCC gets miserly and decides that each HDTV channel will need to fit into a smaller pipe, then we'll need to look to something other than MPEG-2.


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