Comcast HD Quality Reduction: Details, Screenshots - Page 22 - AVS Forum
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post #631 of 2079 Old 04-02-2008, 08:41 AM - Thread Starter
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Originally Posted by alanisrox69 View Post

Fios is for whatever bizzarre reason re-encoding it to a higher bitrate. That's why, in your Matrix shots, the AE screenie of Keanu, his face looks pasty and "flat" looking, like Windows Media Videos....and in the Cable feed, it looks clear with what you say "grain" which is how it's SUPPOSED to look. In the Fios capture it's just getting 'flattened'..... I know it seems bizzarre as a re-encode to a higher bitrate should look transparent...but in this case it is not..........

Please note the first shot in the previous posting was not of the same frame. I noticed that this morning and added a note to disregard the first image.

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Originally Posted by alanisrox69 View Post

I would check some other AEHD stuff.....since it seems Fios is re-processing that channel.

The Comcast feed is clearly not as it is delivered, because there is blocking on the most intense scenes that is not present on the FiOS feed. I have not posted these images because they are not representative of most action on A&E, which still looks very good on Comcast. A&E has the highest bitrate of Comcast's new HD channels, and it's only a 720p channel, so you would expect it to remain quite good with motion.

As far as grain, the FiOS feed of A&E still has grain. It just has noticeably less grain. FiOS could be applying some sort of filter to reduce grain, Comcast could be applying some form of edge enhancement, or it could be a combination of the two. I assumed that Comcast was responsible because the grain was clearly visible on the A&E logo, but I suppose the grain could just be showing through from behind.

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post #632 of 2079 Old 04-02-2008, 08:42 AM
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BFDTV - Comcast seems a bit brighter that FiOS. The picture quality for Comcast looks pretty good. In these series of pictures.

In an email from Tony Werner CTO - Comcast he told me that "During the time of the AVS article we did experience some software problems and interaction with format changes at the source. We are working rapidly to correct these and do believe that we will maintain excellent HD quality."

Have you noticed any improvements in the Comcast picture quality?
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post #633 of 2079 Old 04-02-2008, 08:53 AM
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I still contend you need to be a hypercritical enthusiast (as most here are) to get into a huff about the differences in those latest images. If you go back to those images posted at the beginning of the discussion, there is a 'clear' difference between the two services. Where did all those really ugly macroblocks go? Has Comcast managed to get things adjusted to work better?

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post #634 of 2079 Old 04-02-2008, 08:57 AM - Thread Starter
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HIPAR,

I would agree with you. Someone asked for a comparison of Matrix, so I gave it. A&E is clearly not one of the 'problem' channels on Comcast. The Comcast picture on A&E remains very good with motion, unlike some other channels.

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post #635 of 2079 Old 04-02-2008, 09:03 AM
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Originally Posted by bfdtv View Post

The Comcast feed is clearly not as it is delivered, because there is blocking on the most intense scenes that is not present on the FiOS feed. I have not posted these images because they are not representative of most action on A&E, which still looks very good on Comcast. A&E has the highest bitrate of Comcast's new HD channels, and it's only a 720p channel, so you would expect it to remain quite good with motion.

I would like to see the images you referenced for blocking on Comcast's AE HD

It's time to give props to WLNS for the HD crawl generator!!!

Now we need WHTV to go HD and Lansing's CW to get a separate transmitter so it isn't a digital sub.
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post #636 of 2079 Old 04-02-2008, 09:15 AM
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Originally Posted by bfdtv View Post

A&E is clearly not a problematic channel on Comcast.

sure it is - all their regular programming is stretched.
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post #637 of 2079 Old 04-02-2008, 09:28 AM
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Originally Posted by briansemerick View Post

sure it is - all their regular programming is stretched.

Yes, but that is a different issue. It is an A&E issue, not aComcrap/FiOS/etc. issue.

It appears that 720p is less susceptable to these compression issues than 1080i.

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post #638 of 2079 Old 04-02-2008, 09:41 AM - Thread Starter
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Originally Posted by jefbal99 View Post

I would like to see the images you referenced for blocking on Comcast's AE HD

I will post something or send you a pm as soon as I can. Note however, that I did not see large-scale macroblocking anywhere on A&E. When there was blocking, it was much smaller blocks throughout the image. I don't think you would notice it with moving video.

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Originally Posted by PaulGo View Post

In an email from Tony Werner CTO - Comcast he told me that "During the time of the AVS article we did experience some software problems and interaction with format changes at the source. We are working rapidly to correct these and do believe that we will maintain excellent HD quality."

Have you noticed any improvements in the Comcast picture quality?

I've spent most of my free time this week watching college basketball, Nationals games, and Capitals games, so I have not watched any of the channels in question. I did record a number of different programs late last week, and I downloaded those on Monday and Tuesday, but I have not yet compared them, save for one program on HGTV (see below).

These comparisons are very time consuming. First, the recordings download at just 1.3-1.5MB/s. The recordings are off by a second or two (depending on when the TiVo started to record), so I can't just jump to a specific timecode. I have to find the same frame on both recordings; it is very tedious because I can frame skip forward, but not backward in MPC, so if I move ahead too far, I have to start over. I tried finding the frame in VideoRedo (very easy) and then skipping to that timecode in MPC, but that doesn't work; apparently VideoRedo and MPC keep track of timecodes differently.

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Originally Posted by thoots View Post

Well, last night (Sunday), I tuned in to my favorite two-hour block of HGTV HD shows. And, of course, it seems like HGTV is the most severely impacted channel in my area -- at least, that I've tried. There are a number of HD channels that I don't really watch, so I really can't say how good or bad they are.

But, very simply, what Comcast transmitted last night WAS NOT HIGH DEFINITION. Not even close. I wouldn't even call it "HD Lite." I think it would be best described as "Widescreen Digital Cable." And I presume everyone is aware of how generally awful the 12:1 compressed digital cable service picture quality looks like.

Based on your comments, I recorded several programs from HGTV. Last night, I briefly looked at Over Your Head: Artistic Bathroom.

The recordings from both providers were horrific during motion. Perhaps the FiOS feed was slightly less horrific on some motion, but most of the time, they looked equally bad to me. I can't speak to issues on other HGTV programs, but at least on this series, you cannot blame Comcast. It looks to be a production / source issue.

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post #639 of 2079 Old 04-02-2008, 10:07 AM
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Originally Posted by davehancock View Post

.. It appears that 720p is less susceptable to these compression issues than 1080i.

Wouldn't that make some sense? After you do the arithmetic, there are fewer pixels/second with 720P so you don't have to crank up the compression as much to make it fit into the channel.

I've always thought 720p is less problematic for transmission in a 6 MHz channel but I know the big screeners would be sure to rear up in objection to that.

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post #640 of 2079 Old 04-02-2008, 10:11 AM
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Originally Posted by bfdtv View Post

By uncompressed, they are almost certainly referring to the source signal. All high-definition sources are compressed for distribution via satellite or fiber. But then providers have the choice to compress (recompress) that signal further, potentially sacrificing quality in the process. That's what this thread is about.

Yes, all the ad is saying is that in the context of what is provided to people's homes, the signal is not compressed any further from how they get it.

I'm not sure why everyone is so upset with that ad.

If we want to get technical then we need to start clamoring for the 1.5GB feeds before they even get to the NOC, I mean, come on...

What's really annoying is when a content provider such as Marc Cuban(HDNet) for instance chastises us for complaining about the compression/downrezzing of his channels by telling us we have no idea what "real" HD is as we don't get that uncompressed 1.5GB feed. It was an asinine out of context remark, and for me, it really lowered my opinion of the man.
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post #641 of 2079 Old 04-02-2008, 10:16 AM
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Quote:
Originally Posted by HIPAR View Post

Quote:


Originally Posted by davehancock
.. It appears that 720p is less susceptable to these compression issues than 1080i.

Wouldn't that make some sense? After you do the arithmetic, there are fewer pixels/second with 720P so you don't have to crank up the compression as much to make it fit into the channel.

Not really:
720p: 1280x720X60 = 55,296,000 pixels/sec
1080i: 1920x1080x30 = 62,208,000pixels/sec

That's not a BIG difference.

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post #642 of 2079 Old 04-02-2008, 10:26 AM
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Originally Posted by keenan View Post

Yes, all the ad is saying is that in the context of what is provided to people's homes, the signal is not compressed any further from how they get it.

I'm not an insider, but I have seen before that the distribution signal is a LOT higher (over 36Mbps or higher). The new Comcast thing (was it HTS?) is the only place where low bit-rates were being used.

So, yes, FiOS IS compressing (they have to).

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post #643 of 2079 Old 04-02-2008, 10:31 AM
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Originally Posted by keenan View Post

It was an asinine out of context remark, and for me, it really lowered my opinion of the man.

'Redacted' did it for me.

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post #644 of 2079 Old 04-02-2008, 10:40 AM
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Originally Posted by davehancock View Post

I'm not an insider, but I have seen before that the distribution signal is a LOT higher (over 36Mbps or higher). The new Comcast thing (was it HTS?) is the only place where low bit-rates were being used.

So, yes, FiOS IS compressing (they have to).

Which channels are you talking about? The normal cable and satellite channels are all fed from their respective providers at < 19 Mbps. Verizon is not compressisng their HD. They pass it through as they get it - it's already compressed. (A&E possibly excepted)


Something's definitely funny about A&E. It looks to me like Comcast is applying some sharpening that brings out the grain, while FiOS is softening it, which removes some of the grain.
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post #645 of 2079 Old 04-02-2008, 10:40 AM
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Originally Posted by davehancock View Post

I'm not an insider, but I have seen before that the distribution signal is a LOT higher (over 36Mbps or higher) ...

Wow, it that's the case no one will (Can?) match that. It means FiOS can deliver Blu-ray quality to your home! That also means they can deliver better than broadcast quality if they are receiving a distribution stream at greater than 19 megabits.

If they are doing this when possible, I'll give them their 'uncompressed' claim taking it in the context of what everyone else is doing.

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post #646 of 2079 Old 04-02-2008, 10:47 AM
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Quote:
Originally Posted by davehancock View Post

I'm not an insider, but I have seen before that the distribution signal is a LOT higher (over 36Mbps or higher). The new Comcast thing (was it HTS?) is the only place where low bit-rates were being used.

So, yes, FiOS IS compressing (they have to).

You're talking about the network/content feed? The 45mbps feed(for most of the major nets anyway)? Nobody gets/can get that in their home, at least not with current equipment/technology.

Unless I'm missing something, I'm not really sure where the complaint is at. My take on the ad is that if SciFi sends Verizon a 15mbps signal, then that's what you get in your home. Comcast OTOH, is doing further compression.



I suppose there's some C-band fans out there that can get the 45mbps feed, is that what you mean?
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post #647 of 2079 Old 04-02-2008, 10:59 AM
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Quote:
Originally Posted by HIPAR View Post

Wow, it that's the case no one will (Can?) match that. It means FiOS can deliver Blu-ray quality to your home! That also means they can deliver better than broadcast quality if they are receiving a distribution stream at greater than 19 megabits.

If they are doing this when possible, I'll give them their 'uncompressed' claim taking it in the context of what everyone else is doing.

--- CHAS

The reason that the distribution (usually satellite) is at a lot higher bit-rate is that extra artifacts are introduced with compression if the original bit rate is not at least 2x higher. So IF the local provider (cable) is going to rate-shape there are not additional artifacts introduced.

For example: If A&E (for example) distributes MPEG-2 at 18Mbps, and TW reduces that to 13Mbps, there would be more artifacts than if A&E distributes at 45Mbps and TW reduces that to 13Mbps. This, as I understand it, is pretty normal with HD TV distribution.

The case here, with Comcast, is that they have their own "special" HD signal distribution system, where they do the 3:1 mux at the national head end (I believe it has been called "head end in the sky"). That head end is also receiving the 45Mbps distribution from A&E and the like and is doing statistical multipexing there, cramming the 3 HD channels into one bitstream that can go right to a QAM with no additional processing at the local cable head end.

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post #648 of 2079 Old 04-02-2008, 11:09 AM
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Quote:
Originally Posted by keenan View Post

You're talking about the network/content feed? The 45mbps feed(for most of the major nets anyway)? Nobody gets/can get that in their home, at least not with current equipment/technology.

Yep, that's (more or less) what I'm talking about. Now that you mention 45mbps, I think that may be the right number.

Quote:
Originally Posted by keenan View Post

Unless I'm missing something, I'm not really sure where the complaint is at. My take on the ad is that if SciFi sends Verizon a 15mbps signal, then that's what you get in your home. Comcast OTOH, is doing further compression.

No, what I am saying is that SciFi sends a 45mbps signal.

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post #649 of 2079 Old 04-02-2008, 11:20 AM
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Quote:
Originally Posted by davehancock View Post

The case here, with Comcast, is that they have their own "special" HD signal distribution system, where they do the 3:1 mux at the national head end (I believe it has been called "head end in the sky"). That head end is also receiving the 45Mbps distribution from A&E and the like and is doing statistical multipexing there, cramming the 3 HD channels into one bitstream that can go right to a QAM with no additional processing at the local cable head end.

Are you sure that all Comcast areas receive programing through HITS (Headend in the Sky)?

I thought HITS was a service for small cable companies that allow them to offer digital programming without as large of a capital outlay.
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post #650 of 2079 Old 04-02-2008, 11:27 AM
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Originally Posted by davehancock View Post

Yep, that's (more or less) what I'm talking about. Now that you mention 45mbps, I think that may be the right number.

No, what I am saying is that SciFi sends a 45mbps signal.

Okay, that's what I thought. SciFi is probably a bad example as I believe NBC/Universal does their own flavor of "3-packing" with their distribution signals, but in general yes, there is a higher bitrate signal "available". But for practical application in regards to this thread, and what the public can get in their home, 19.38mbps is the generally accepted rate of an "uncompressed" signal. In that context, the FiOS ad is truthful.

I'm not defending any of these providers, personally, I want that 1.5GB feed in my HT room.
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post #651 of 2079 Old 04-02-2008, 11:28 AM
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Quote:
Originally Posted by PaulGo View Post

BFDTV - Comcast seems a bit brighter that FiOS. The picture quality for Comcast looks pretty good. In these series of pictures.

In an email from Tony Werner CTO - Comcast he told me that "During the time of the AVS article we did experience some software problems and interaction with format changes at the source. We are working rapidly to correct these and do believe that we will maintain excellent HD quality."

Have you noticed any improvements in the Comcast picture quality?

This smells like doubletalk to me. You're trying to stick 57 Mbps of traffic into 38 Mbps of pipe. Something is going to give here! Maybe the settings were worse than they needed to be, but there is going to be degradation here - something has to give.

Unless of course you believe the original encoding of the programs was so bad that transrating wouldn't actually hurt anything, which I don't believe is the case here.

As for maintaining excellent quality, if the do the same job on HD that they do on SD, excellent isn't the word I would use.

If he was going to be direct he should have just said it shouldn't have sucked as badly as it did, just sucked modestly badly.

The bottom line is that this all shows the how bad a spot they are in when compared to their competition. They still are acting like they have a monopoly - that they can degrade quality as much as they like because consumers don't have another choice. Certainly anyone who has the option of FIOS should take it in a heartbeat, regardless if they care about fast internet or not, but just for video quality.

And it appears the same can be said for DirecTV, though if they were smart, they'd furnish us the raw h.264 streams for the same programs that are being compared from VZ and Comcast, and that would confirm what many of our eyes are telling us, that DirecTV has a quality advantage in HD over Cable. If they were smart of course.
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post #652 of 2079 Old 04-02-2008, 11:30 AM
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Originally Posted by homcom View Post

Are you sure that all Comcast areas receive programing through HITS (Headend in the Sky)?

I thought HITS was a service for small cable companies that allow them to offer digital programming without as large of a capital outlay.

Nope. Most all MSO's take their feed from HITS. The only other option is for individual headends to take the signal directly from the programmers via satellite (which they can do for some of the HD channels), or distribute the video via fiberoptic network, but that requires full fiber connectivity to all headends, which isn't usually the case for video service.
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post #653 of 2079 Old 04-02-2008, 11:31 AM
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Quote:
Originally Posted by homcom View Post

Are you sure that all Comcast areas receive programing through HITS (Headend in the Sky)?

I thought HITS was a service for small cable companies that allow them to offer digital programming without as large of a capital outlay.

It was/is, it's just that Comcast has started to "buy retail" from their own off the shelf product as well as sell it to other cablecos.

CMC/HITS is a Comcast company.
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post #654 of 2079 Old 04-02-2008, 11:32 AM
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bfdtv, can you post comparison screenshots for the Matrix scene with the explosion coming out of the elevator, since that is easily the most difficult to compress scene in the movie? Also, can you get a comparison for one of A&E's HD reality shows? 24p content on 720p can take a lot of abuse before any real problems come as we can see when Fox gets down around 10Mbit/s, but 60p will degrade much sooner.
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post #655 of 2079 Old 04-02-2008, 11:34 AM
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Has anyone noticed any problem the the quality of Comcast VOD? I have not seen any quality problems with their VOD service. Since some VOD (at least in my area) is delivered in clear QAM someone with the proper equipment someone should be able to measure it.

I also wonder if their switch video service will also allow for more bandwidth for each channel. Based upon the way I think it works they really do not need to over compress the switched video signal since the signal is delivered through fiber to a local node.
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post #656 of 2079 Old 04-02-2008, 11:34 AM
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.. a 3 channel stuffed QUAM equivalent, thinking Starz Max or Showtime for instance, or is on demand content compressed somewhere during distribution like the rest of their regular programming?

Thanks in advance.

Signed, 1st post newbie.
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post #657 of 2079 Old 04-02-2008, 11:36 AM
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Whoops, PaulGo beat me to the punch. Darn!
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post #658 of 2079 Old 04-02-2008, 11:42 AM
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Quote:
Originally Posted by davehancock View Post

Not really:
720p: 1280x720X60 = 55,296,000 pixels/sec
1080i: 1920x1080x30 = 62,208,000pixels/sec

That's not a BIG difference.

A lot of content is shot at 24fps. So, in many cases, you're really looking at the equivalent of 1280x720x24 and 1920x1080x24 with the remaining frames being repeats of other frames.
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post #659 of 2079 Old 04-02-2008, 11:48 AM
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Quote:
Originally Posted by PaulGo View Post

Has anyone noticed any problem the the quality of Comcast VOD? I have not seen any quality problems with their VOD service. Since some VOD (at least in my area) is delivered in clear QAM someone with the proper equipment should be able to measure it.

I also wonder if their switch video service will also allow for more bandwidth for each channel. Based upon the way I think it works they really do not need to over compress the switched video signal since the signal is delivered through fiber to a local node.

Interesting experiment to do. If the source of the VoD comes from HITS, then it's compromised just like the broadcast version (even though it doesn't save much in terms of plant capacity). It could be distributed by an auxilary network though, in which case it would bypass HITS and it's associated transrating.

VoD is definitely fed by another network at least in part, because there are a ton of programs available that never aired via a linear channel. So I suspect that if they built a network for that, they probably distribute all the stuff differently too.

HITS certainly advertises it's capabilities to feed VOD systems (look here: http://www.comcastmediacenter.com/in...livery/VOD.htm
) but I don't know how many MSO's use it for that. I suspect Comcast does, as HITS is part of Comcast, but it's not clear they would use the same adulterated source of programming to feed VOD.

It would be easy enough to capture via R5000-HD though. Much harder via Tivo.
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post #660 of 2079 Old 04-02-2008, 11:50 AM
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Originally Posted by neo1022 View Post

A lot of content is shot at 24fps. So, in many cases, you're really looking at the equivalent of 1280x720x24 and 1920x1080x24 with the remaining frames being repeats of other frames.

No, when it's broadcast, those repeat frames count as video information. Once it's sent out at 60fps, you get 60fps. Not only that, the networks aren't playing back film - they're playing back video tape at their broadcast frame rate. The original source material is irrelevent for this test.


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