Comcast Begins Converting 1080i Channels to 720p to "deliver superior video."

[Naiera]

Originally Posted by Keenan

Possibly your TV is doing a terrible job and that might be why you're not seeing a difference? Just a thought.

That's cute. I have a Lumagen RadianceXD feeding a JVC X30 projector.

Just because a 1080i signal is de-interlaced it does NOT mean it's equal to a 1080p signal. It's not just math.

[Naiera]

Originally Posted by dubious

You have to keep in mind, these channels transitions are being performed by Comcast and not at the source, so the end result is less than ideal since their 720p channels are sourced from 1080i feeds. ABC and Fox that provide native 720p feeds still look far superior by comparison.

Well, that's a problem, of course. It should be 720p natively. That would mean superior HD for errbody and less bandwidth spent getting it out there.

[#Darren]

I have been saying for YEARS that this was the FUTURE of streaming sites. That they would never beat disk based media quality. Most people just ignored me like I was talking crap...

[dubious]

Originally Posted by Naiera

That's cute. I have a Lumagen RadianceXD feeding a JVC X30 projector.

Just because a 1080i signal is de-interlaced it does NOT mean it's equal to a 1080p signal. It's not just math.

When the fields match, the luminance data of 1080i is 225% that of 720p. 1080p definitely offers benefits of dropping blended fields and accurate chroma, but that hardly qualifies a 225% drop in grey-scale resolution to put 720p on a pedestal as superior delivery format over 1080i. In motion 1080i looks much better in motion, I can really only notice interlacing when I hit freeze frame on my tv and stand a foot away from it. Interlacing is far more noticeable on 720p native channels that run interlaced advertisements presented in a field-blended mess of upscaled frames. If normal 1080i looked anything like an interlaced source field-blended in a 720p signal, I'd be inclined to agree with you, but it doesn't.

[jacobsever]

Originally Posted by #Darren

I have been saying for YEARS that this was the FUTURE of streaming sites. That they would never beat disk based media quality. Most people just ignored me like I was talking crap...

Wait, what?

Comcast isn't turning all of the streaming sites quality into 720p if that's what you're thinking. Comcast is turning their digital cable service into 720p. If you use their internet, you'll still be able to stream via Netflix/HBO Go/Hulu/whatever at 1080p and even 4K.

[Naiera]

Originally Posted by dubious

... but that hardly qualifies a 225% drop in grey-scale resolution to put 720p on a pedestal as superior delivery format over 1080i.

We are, obviously, talking about these delivery formats when used with the same, fairly limited bitrate, like most TV signals. In this situation, ie the real world, 720p is better.

[dubious]

Originally Posted by Naiera

We are, obviously, talking about these delivery formats when used with the same, fairly limited bitrate, like most TV signals. In this situation, ie the real world, 720p is better.

I noticed the change from MPEG-2 1080i to MPEG-4 720p, so while bitrate may have a place in this argument, the basic assessment known as eyeballs says otherwise.

[Naiera]

And this change included the source material going from 1080i to 720p?

[dubious]

Originally Posted by Naiera

And this change included the source material going from 1080i to 720p?

Yes, the transition was Comcast moving their channels to MPEG-4 as well as 720p.

Basically, based from what I read on the TiVo forums regarding this issue, is that Comcast was transmitting 4x MPEG-2 1080i30 channels per QAM channel in the prior configuration. Moving to MPEG-4 would essentially allow them to cut the bitrate per channel in half, allowing 8x MPEG-4 1080i30 channels to be stuffed into a single QAM. However, if you change the broadcast stream from 1080i30 to 720p60, you can stuff 9x MPEG-4 720p60 streams into a single QAM.

Comcast has cheaped out on their infrastructure upgrades over the years, so in order to expand channel offerings and broadband speeds, they need to free up QAMs. By stuffing more channels into each QAM they can offer "more" service over "better" service. A QAM is a constant bitrate modulation format with a capacity of 38.8 Mbits/sec.

Comcast also uses a variable channel bitrate system, so it can allot more bitrate to a channel showing an action movie over a news channel with static overlays, etc. This shift of bitrate allotment can only be shared by channels in the same QAM though, and all channels together are encoded together in the 38.8 Mbits/sec QAM.

So bascially, in the older MPEG-2 1080i30 QAM configuration, each HD channel used 25% of a QAM on average. If the transition had been to MPEG-4 and retaining 1080i30, then each HD channel would have used 12.5% of a QAM on average. In the new configuration, each of the MPEG-4 720p60 channels uses 11.11% of a QAM on average.

So Comcast was essentially giving MPEG-2 1080i30 channels 9.7 Mbits/sec.

If they had migrated to MPEG-4 1080i30 and doubled the number of channels in the QAM, this would equate to 4.85 Mbits/sec.

... instead they migrated to MPEG-4 720p60 with 9 channels per QAM, which is 4.31 Mbits/sec.

Don't quote me for accuracy, I'm relaying and simplifying information here from other forums I've read, but those numbers are the breakdown as far as I understand it at the moment.

1920*1080 = 2073600; * 30 FPS = 62208000; * 8 Channels = 497664000
1280*720 = 921600; * 60 FPS = 55296000; * 9 Channels = 497664000

[Naiera]

Originally Posted by dubious

Yes, the transition was Comcast moving their channels to MPEG-4 as well as 720p.

Wouldn't the channels themselves have to send Comcast something else than 1080i?

[Keenan]

Originally Posted by Naiera

Wouldn't the channels themselves have to send Comcast something else than 1080i?

No, for 90% of the cablenet channels Comcast provides they are collected at a facility in Colorado where they are converted, down-converted, manipulated, whatever into the format that will be delivered to the various markets around the country. It's at this facility where they will be down-rezzed and re-compressed to smaller bitrates/payload sizes. Comcast also sells channel packages to other cable systems so it could very well be that other cable providers will be seeing the same down-rezzing of 1080i channels.

The MPEG4 switch is perfectly fine, in fact, most all networks have been sending their signals out as MPEG4 for some time anyway, I believe HBO has been doing it for over a decade now. It's the down-converting of image quality that I object to, just to squeeze an extra channel's worth a bandwidth out of the finite amount of bandwidth they have.

[dubious]

While no comment on the future of the on-demand delivery format has been spotted yet, I've migrated over to watching the shows I'm interested in through on-demand.

Westworld has so far been offered in 1080i as GoT has been previously, and 1080i was pretty standard for on-demand HD content before this transition.

However, when I pulled up Ash vs Evil Dead Ep. 202 today, the feed was 1080p 24hz. That form of encoding has been available before, but was usually reserved for the premium "get it before blu" type new releases that go for $20.

So, it's interesting, and worth noting for now, Comcast customers may want to use on-demand to get the best picture quality option for their shows.

[netnothing]

I for one, with a 4K TV, have started to resort to streaming services for some shows as the Comcast signal is just plain bad. This isn't really a 1080i vs 720p argument. It's more the amount of compression and lower bandwidth Comcast has switched these channels to.

A 720p Hulu stream, is light years better than my local Fox signal at 720p. And this channel is still MPEG-2. I believe services such as HBO Go and Showtime Anytime also max at 720p. You cannot compare the Comcast signal to those. Comcast is just plain bad.

We also have a couple series recorded from Lifetime and AMC from over the summer when they were MPEG-2 and 1080i. The recordings are also much clearer than what is being provided today on those channels after the switch.

If you have a 4K TV, as of today it's an embarrassment to watch much of what Comcast delivers.

-Kevin