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HDTV Bandwidth requirements

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Anonymous
August 28, 2005 1:42:38 PM

Archived from groups: alt.video.ptv.tivo (More info?)

It's my understanding--if I'm wrong correct me on this--that HDTV requires 4
times the bandwidth of SDTV, and that a digital TV broadcast requires
one-fourth the bandwidth of an analog TV broadcast of the same resolution.

If this is correct, then it would seem that TV channel assignments for HDTV
occupy the same bandwidth as the current analog SDTV, and that digital
broadcasters have the option of using that bandwidth to send 4 SDTV pictures
in digital form, or just the one in HDTV.

I can imagine that the broadcast and cable industry will often prefer to
send more programs, and send them in standard definition, saving high
definition for first run prime time offerings.

Is any of this correct?

Norm Strong
August 29, 2005 12:35:42 AM

Archived from groups: alt.video.ptv.tivo (More info?)

<normanstrong@comcast.net> wrote in message
news:D K6dnX8EfKvjdIzeRVn-iQ@comcast.com...
> It's my understanding--if I'm wrong correct me on this--that HDTV requires
> 4 times the bandwidth of SDTV, and that a digital TV broadcast requires
> one-fourth the bandwidth of an analog TV broadcast of the same resolution.
>
> If this is correct, then it would seem that TV channel assignments for
> HDTV occupy the same bandwidth as the current analog SDTV, and that
> digital broadcasters have the option of using that bandwidth to send 4
> SDTV pictures in digital form, or just the one in HDTV.
>
> I can imagine that the broadcast and cable industry will often prefer to
> send more programs, and send them in standard definition, saving high
> definition for first run prime time offerings.
>
> Is any of this correct?
>
> Norm Strong
>

DirecTV going to switch all of their HDTV channels to mpeg4 encoding
(eventually) so they can get the same quality with half the bandwidth that
current HD streams use. Cable companies and other TV service providers will
probably be doing to same.
Anonymous
August 29, 2005 3:35:23 AM

Archived from groups: alt.video.ptv.tivo (More info?)

(normanstrong@comcast.net) wrote in alt.video.ptv.tivo:
> It's my understanding--if I'm wrong correct me on this--that HDTV requires 4
> times the bandwidth of SDTV, and that a digital TV broadcast requires
> one-fourth the bandwidth of an analog TV broadcast of the same resolution.

Not quite.

Good quality real-time encoded 480i MPEG-2 requires at least 4Mbps, and
more like 6Mbps. Current digital TV in the US can put 19.3Mbps in one
6MHz TV channel, while analog puts one 480i channel in the same bandwidth.

So, 480i digital takes about 25-30% of the "bandwidth" of 480i analog.
On a cable system using 256QAM, they can put 40Mbps in a 6MHz channel, so
480i digital would only take 12-15% as much as the analog there.

Good quality 720p HD takes at least 12Mbps, and 15Mbps is a more reasonable
minimum. Good quality 1080i takes at least 15Mbps, and even 28Mbps isn't
enough to eliminate all artifacts (based on D-Theater tape bitrates and
quality).

> I can imagine that the broadcast and cable industry will often prefer to
> send more programs, and send them in standard definition, saving high
> definition for first run prime time offerings.

It's a thought, and some stations are trying it, but in any given market,
there are only 100% of the total eyeballs available to watch TV. Splitting
your channel into 4 means that people pick *one* of your channels and
you essentially get the same total ratings for the bandwidth, on average.

The only thing that might work is if stations get home shopping channels
to pay for that bandwidth with the payment a flat fee that is not related
to ratings.

--
Jeff Rife | "Wow, I've never seen you this
| bitter...I like it."
|
| -- Richard Karinsky, "Caroline in the City"
Related resources
Anonymous
August 29, 2005 4:35:58 AM

Archived from groups: alt.video.ptv.tivo (More info?)

eric (eric.2@cox.net) wrote in alt.video.ptv.tivo:
> DirecTV going to switch all of their HDTV channels to mpeg4 encoding
> (eventually) so they can get the same quality with half the bandwidth that
> current HD streams use.

Actual real-time encoding samples show that the reduction in bitrate for
the same quality is far lower than this. A 720p stream that needs 15Mbps
with MPEG-2 will need 10-12Mbps with MPEG-4. At 8Mbps, it becomes noticably
lower quality.

> Cable companies and other TV service providers will
> probably be doing to same.

Unfortunately, cable TV can never go to MPEG-4 without FCC permission
because CableCard digital cable tuners must be able to decode every channel,
and they have no ability to decode MPEG-4 because it isn't part of the spec.

--
Jeff Rife | "She just dropped by to remind me that my life
| is an endless purgatory, interrupted by profound
| moments of misery."
| -- Richard Karinsky, "Caroline in the City"
August 29, 2005 4:35:59 AM

Archived from groups: alt.video.ptv.tivo (More info?)

"Jeff Rife" <wevsr@nabs.net> wrote in message
news:MPG.1d7c5abb49d307bf989f5b@news.nabs.net...
> eric (eric.2@cox.net) wrote in alt.video.ptv.tivo:
>> DirecTV going to switch all of their HDTV channels to mpeg4 encoding
>> (eventually) so they can get the same quality with half the bandwidth
>> that
>> current HD streams use.
>
> Actual real-time encoding samples show that the reduction in bitrate for
> the same quality is far lower than this. A 720p stream that needs 15Mbps
> with MPEG-2 will need 10-12Mbps with MPEG-4. At 8Mbps, it becomes
> noticably
> lower quality.
>

Thanks for the info. Cable companies should gain a TON of bandwidth when
they stop sending analog TV signals, but who knows when that will happen.
Anonymous
August 30, 2005 6:52:17 AM

Archived from groups: alt.video.ptv.tivo (More info?)

normanstrong@comcast.net wrote:

> I can imagine that the broadcast and cable industry will often prefer to
> send more programs, and send them in standard definition, saving high
> definition for first run prime time offerings.
>
> Is any of this correct?

KQED, the PBS station in San Francisco, has been doing exactly that
for more than a year now. During the evenings, it broadcasts one HD
subchannel and one SD subchannel. The rest of the day it broadcasts
four SD subchannels.

http://www.kqed.org/tv/digitaltv/index.jsp

Digital 9.1 = KQED HD (widescreen), airs 8pm to 6am.
Digital 9.2 = KQED Encore (SD), airs 24 hours.
Digital 9.3 = KQED World (SD), airs 6am to 8pm.
Digital 9.4 = KQED Life (SD), airs 6am to 8pm.
Digital 9.5 = KQED Kids (SD), airs 6am to 8pm.

The cable industry does not use ATSC. Digital cable is not limited
to the 6 MHz bandwidth that analog cable uses; they have more
latitude in allocating bandwidth as they see fit.

-Joe
!