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Old November 28th, 2007, 02:03 PM   #1
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HDV artifacts on national TV

Hey guys,

I see a lot of the typical 'blocking' artifacts on such channels as Discovery HD, National Geographic HD, etc, where the long-GOP compression causes the quality to drop drastically for half a second or so if there is a major change to the screen, such as someone quickly walking in front of the camera.

Do you think the majority of these are due to the documentary nature of these shows, and them actually using HDV/long-GOP compression on a regular basis, or more likely the compression on delivery from my cable provider (comcast)?

I'm really just curious as to whether this is considered acceptable in national programming, documentary or not, or is more of a delivery-medium issue, and wanted to see if anyone had an opinion or some behind-the-scenes knowledge of this. :)

Carl
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Old November 28th, 2007, 02:23 PM   #2
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While it is certainly possible for HDV to make it on national TV there is not supposed to be a ton of it. I would expect it more on the documentary style shows though. I have seen it on some prime time shows via bright house. One way to test is to use over the air signals. If I understand correctly it is supposed to be uncompressed.
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Old November 28th, 2007, 02:34 PM   #3
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Really? It was my understanding that the HD channels coming in through cable were compressed with some version of mpeg, but I'm no expert.

I've noticed the blocking mainly on documentary styled shows, but I think on a few others as well. Don't quote me on that though, I need to do more research (i.e. do more couch potato-ing :D )

Cheers to another DVinfo type in Florida!

Carl
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Old November 28th, 2007, 03:26 PM   #4
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HD Cable is Very Compressed!!!

I have read of data rates on digital cable somewhere in the 19mb/s--less than HDV rates!! Even with superior encoders the HD signals are very limited in quality currently (and cable operators want to give you more channels, esp. pay-per-view rather than better quality)! That's what makes all of the recent fuss over screen displays of 1080i versus 1080p so funny--no signal available to your home is of enough quality to tell the difference. It also makes some of the concern by some networks over accepting HDV footage seem silly.

Eventually bandwith will grow and compression algorithims will improve, but as of now my HDV picture is often superior to HD cable!
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Old November 28th, 2007, 03:53 PM   #5
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Gotta love it! That is corporatism at work, for sure.

Unfortunately means that I'm not seeing a bunch of HDV artifacts, which would mean a pattern of greater acceptance....

Still waiting for that Cineform recorder myself, who cares what it was shot on if it's captured straight to a DI. :)

Carl
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Old November 28th, 2007, 03:59 PM   #6
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Originally Posted by Robert Altman View Post
I have read of data rates on digital cable somewhere in the 19mb/s--less than HDV rates!! Even with superior encoders the HD signals are very limited in quality currently (and cable operators want to give you more channels, esp. pay-per-view rather than better quality)! That's what makes all of the recent fuss over screen displays of 1080i versus 1080p so funny--no signal available to your home is of enough quality to tell the difference. It also makes some of the concern by some networks over accepting HDV footage seem silly.
The data rate for over the air is around 19.2mbs. If you're talking cable or satellite HD, drop that to around 11 or 12 mbs. It's transmitted as MPEG2 Transport Stream. That's why you get the motion artifacts and stuff. I would never watch ABC, CBS, NBC, FOX from cable or satellite if the local station transmits in digital such as they do here in Dallas.

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Old November 28th, 2007, 06:33 PM   #7
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As has been said, the bandwidth limit is 19.2Mbps. Cable companies usually use slower rates like around 15Mbps, which is still not that bad. DirecTV uses 10-12Mpbs and 1280x1080 frame size, but they also use MPEG4 compression which is supposedly superior than MPEG-2 (think AVCHD, do you really believe that it is better than HDV?). They recompress to MPEG4 from original signal, thus introducing generation loss.

Then, satellite providers and many cable providers recompress the signal again in the set-top box. Granted, this does not seem to happen to all programming, but only to programming that has different format that the format selected by a user on a box. I never could get this, and still cannot: why a user should select 1080i/720p/480p/480i explicitly while all TVs are perfectly capable of processing these formats? This is just plain stupid.

Anyway, 19Mpbs is barely sufficient for 720p, it is not sufficient for 1080i when you have complex details or a lot of motion. 1080i in the 19Mbps Procrustean bed simply does not work well. Try watching football, when they pan over the stands with a lot of spectators, the picture is just a mess. I noticed that cameramen try not to do fast pans anymore and use a lot of closeups on the players with shallow DOF to minimize the bitrate.

Over-the-air quality is the best, then goes cable, then goes satellite. Cable and satellite providers simply pull original MPEG-2 off the air to retransmit local programming.
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Old November 28th, 2007, 06:40 PM   #8
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Thanks for the awesome breakdown!

I'm trying to make sure I keep these sort of things in mind as I work to get HD television contracts... just because I can give it to the buyer in pristine HD.... I know what it tends to look like before it makes it to a home! :)

Carl
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Old November 28th, 2007, 07:30 PM   #9
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I see artifacts on SD all the time (Directv). On some channels, it really is disgraceful. Frankly, the technical requirements for "broadcast" quality in the US are laughable in comparison to other places.

But, then again most of the content is drivel, so it doesn't really matter :O)
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Old November 29th, 2007, 12:42 PM   #10
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Originally Posted by John Miller View Post
I see artifacts on SD all the time (Directv). On some channels, it really is disgraceful. Frankly, the technical requirements for "broadcast" quality in the US are laughable in comparison to other places.
http://www.widemovies.com/directvcomp.html (I am not affiliated with this site). Granted, images are quite dated, but I don't think that the quality has improved since then ;)
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Old December 7th, 2007, 12:08 AM   #11
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Quote:
Originally Posted by Robert Altman View Post
I have read of data rates on digital cable somewhere in the 19mb/s--less than HDV rates!! Even with superior encoders the HD signals are very limited in quality currently (and cable operators want to give you more channels, esp. pay-per-view rather than better quality)! That's what makes all of the recent fuss over screen displays of 1080i versus 1080p so funny--no signal available to your home is of enough quality to tell the difference. It also makes some of the concern by some networks over accepting HDV footage seem silly.

Eventually bandwith will grow and compression algorithims will improve, but as of now my HDV picture is often superior to HD cable!
Well the debate is for the next-gen DVD players, on which you can tell a difference.
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