[opendtv] Re: Finally anamorphically compressed 480i

  • From: Craig Birkmaier <craig@xxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Wed, 26 Jan 2011 08:49:17 -0500

At 9:17 AM -0500 1/25/11, Hunold, Ken wrote:

Regarding a glitch when decoders lock to the new source, my cable box
switches from 720p and 1080i sources to 480<something> all the time,
when the cable company splices a local spot into a national feed.  I
notice no glitch.  I even saw a broadcaster do that with/to their MPEG
encoder, and believe it or not, it worked.  (I would have never thought
this was possible, not because of any broadcaster stubbornness, but
rather the inability of the encoder and multiplexer to "play nice.")
When my cable box changes format the TV breaks up while locking to the new format. It is a Scientific Atlanta HD explorer.
I have never seen a glitch on any Cox Cable HD channel, although when I switch between a 720P channel and a 1080i channel there is a glitch. I believe Cox is upconverting any SD spots to the correct HD format before splicing it into the stream.
For a decoder to operate without glitches when splicing different formats together is a daunting task. I've never seen it done. All the buffering changes and the display processor must do a frame accurate cut to the new scaling factors. Maybe I am behind the times, but this is rather complex. 



Also, during these stream splices the audio changes from 384 or 448 kbps
5.1 audio to 192 kbps stereo with nary a pop or crash.  It *can* be
done.
Audio is a bit easier, although the signal is continuous, so there is no real switch point - hopefully both the from and to sources are silent at the cutover point. 


To be clear, I do not work for either PBS or Fox.  My suspicion as to
why the Agilevision system that was used by some PBS stations was not
successful was because the thing was just too darned expensive, not
because of broadcaster inertia.  You're talking about ten years ago,
give or take.  Splicer systems are much cheaper today, and you can make
a good case that the Fox system does a better job of delivering a better
viewer experience than "traditional" concatenation strategies.
Is Fox not 720P all the time? I strongly believe they upconvert 4:3 SD to 720P before splicing it in, usually in pillarbox - They do this all the time on Fox New Channel (HD) for commercials, although they run a distortion algorithm on 4:3 sources to fill on screen graphic windows...
As for Agilevision, cost may have been a factor, but local commercial broadcasters were totally against the concept... Most still are. They want the comfort factor of local control of the streams, and few if any are using splicing techniques. 



There are many examples of where a technology (or even a programming
idea) is just too far ahead of its time.  And don't use this as a
jumping-off point for the 8VSB/COFDM argument...


Moi?
The real issue is knowing where you are headed and what the correct infrastructure is for any new technology. Trying to force fit an old business model into a new technology usually results in sub optimal results. 

Regards
Craig


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