[opendtv] Re: Mediaflo Technology
- From: "Allen Le Roy Limberg" <allimberg@xxxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Fri, 10 Nov 2006 13:10:59 -0500
Comparing resolution of analog and digital systems on a pixel per line count
ignores the important fact that edge position resolution is not
pixel-bounded in the analog transmission. No quantum shifts as in a digital
sampled-data transmission.
Al
----- Original Message -----
From: "Craig Birkmaier" <craig@xxxxxxxxx>
To: <opendtv@xxxxxxxxxxxxx>
Sent: Friday, November 10, 2006 11:22 AM
Subject: [opendtv] Re: Mediaflo Technology
> At 11:02 AM -0500 11/9/06, Mark Aitken wrote:
> >In-line response.
> >
> >Craig Birkmaier wrote:
> >>14 live streaming national interest
> >>5 live streaming local interest
> >>
> >>50 national and 15 local services that will deliver ~20 minutes of
> >>content per day to receiver cache.
> >What does local mean?
>
>
> I presume that this is content that is localized to the specific
> transmitter - for now it looks like Mediaflo will have one
> transmitter per market served; later they claim they will build out
> SFNs around markets. There is more detail about the service
> opportunities in the resources on the website, however, it is
> important to note that MediaFlo is NOT the operator of the system,
> per se. They are offering the service to existing system operators in
> each market as an adjunct to a cellular service. The operator in each
> market will have a strong say in what is carried, and the ability to
> partner with local content providers within that market to fill the
> "local" channels.
>
> >NTSC is 'effectively' 320 x 240? Really?
>
> You could argue that there is more horizontal resolution, but not
> vertical resolution The cable guys started out with 1/2 D1 MPEG-2
> encoding, which was 352 samples per line. I looked at several sites
> about the horizontal resolution of NTSC and the consensus sees to be
> about 330 dots per screen width when transmission losses are taken
> into consideration.
>
> There are two factors at work here:
>
> 1. Transmission bandwidth - Ron did the math to show what is
> "possible " if you can receive an NTSC signal perfectly. About 440
> pixels per line. The 240 pixels vertically does not take into account
> any positive benefit from "the interlace factor," which could add a
> bit more vertical detail, however, with Mediaflo, the signal must be
> de-interlaced for encoding as 320 x 240 progressive frames, thus it
> is unlikely that any additional detail will make it through the
> conversion process.
>
> 2. NTSC displays - the typical NTSC receiver has no more than 330
> dots/stripes per screen width. With higher quality tubes (usually
> with S-video inputs) the number of dots/stripes may increase to
> approximately 450-500.
>
> Bottom line, you are wasting bandwidth if you are inputting more than
> 480 samples per line into an NTSC encoder. We can use the full 704
> samples per line (ATSC) if we are encoding for DTV, but even here
> this may be overkill if we don't provide enough channel bandwidth
> (bit rate) to assure that the detail makes it through the encoder.
>
> MediaFlo says that the input source for their network will be
> primarily from satellite, and they expect MPEG-2 encoding at 704 x
> 480 or 720 x 480. If this stuff is not overly compressed, there
> should be enough detail left to produce a much higher quality 320 x
> 240 progressive stream than would be possible if one started with
> NTSC source (analog or encoded using MPEG-2).
>
> This all brings back memories from the early '90s when we noted that
> a properly encoded 480P signal (i.e. 854 x 480) would provide a very
> high quality viewing experience comparable to HDTV on many consumer
> displays.
>
> How quick we forget how poor NTSC quality actually is...
>
> Regards
> Craig
>
>
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