[opendtv] [Fwd: RE: [oldvtrs] So Much for HDTV]

...more from the old VTR list on compression:

Compression is a great tool; there would not be D-Beta, HDCam, and HD-D5
etc if compression did not exist. But tape compression is a whole
different discussion.

What’s happened is that this technology has given non-technical station
managers the ability to do really stupid things.

Here in NY, we have two stations that have HD-plus-two-SD muxed in their
19.4 Mb of channel capacity. One station is 720P, so the artifacts are
manageable but the other is 1080I and, I don’t care how much statmux you
apply, it just doesn’t look very good when things start to move.

Since 1995, we have had the opportunity to conduct numerous formal image
quality tests on every broadcast MPEG-2 encoder made. Using the entire
available DTV channel for only one program results in a peak video
availability of approx 18.3 Mbps. In my opinion, this is not enough bits
to cleanly compress 1080I 4:2:0 during cross fades which is the most
stressful video transition to code.  I have to hand it to CBS here in NY
who has been able to maintain one-program-only in their DTV channel.

With Gen-3 MPEG-2 encoders now in the market, you need to be around
25-30 Mbps to get the process to the point where an expert observer
would have trouble seeing artifacts.



An appropriate compression expression might be: /Just because you can
doesn’t mean you should./

John Turner

//Principal Engineer//

Turner Engineering, Inc.
___________________

On Tue, 2008-08-19 at 02:15 -0400, Cliff Benham wrote:
> Tony Quinn wrote:
>
> > That's nothing to do with HD per se, the sole cause of that is a
> lack of
> > bitrate allocated to the MPEG stream.
>
> It is just as you say. It's happeniing everywhere on DirecTV, Dish,
> all
> the digital channels on cable systems and fiber systems as well. Not
> only the HD programs but SD as well, and it looks worse there.
>
> Some individual streams carry an HD sports program plus 4 or 5 SDI
> programs as well. The programmers feel they have to squeeze all the
> programs they can into the system to make money, never mind about the
> pixilation when fading to black or blockiness when the camera pans
> the
> basketball court.
>
This is precisely why I have always said, 'Compression is evil'.

Tim Stoffel



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