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Re: [Discuss-gnuradio] MovieBeam
David I. Emery
Re: [Discuss-gnuradio] MovieBeam
Fri, 2 Jun 2006 17:40:43 -0400
On Fri, Jun 02, 2006 at 10:30:36AM -0700, Matt Ettus wrote:
> Just read about MovieBeam on Slashdot. They mention that it
> "piggybacks" on a PBS signal. I assume they mean a digital TV channel,
> but they have a very small antenna.
While I have no specific inside information at the moment, I am
almost certain this is a matter of dedicating some percentage of the 19
Mb/s ATSC transport stream bandwidth on the over the air channel to TV
over IP and writing the data to the disk in the box 24/7 as a continuous
"background" task. Pretty clearly not real time delivery of the
Obviously basically a means of funding PBS stations, unclear as
to what percentage of the OTA bandwidth it uses or whether this is
dynamically assigned (replacing (otherwise) null packets in the
transport stream) or a fixed partition which obviously will degrade best
possible HDTV quality somewhat.
I do have tools to look at the transport stream here for our
(famous - WGBH) PBS stations in Boston, maybe I'll fire them up.
Obviously the very very strong presumption is that the IP stream is
completely encrypted or at least the movie files it contains are tightly
encrypted so without the right keys they aren't accessible to be hacked
PBS has long carried program guide information for GEMSTAR in
its analog signals in the vertical blanking interval data transmission
zone. And many VCRs can use this stream to set the time of day (no
blinking 12:00 AM).
TV over IP is very much the coming thing in the broadcast
industry and PBS is up front as one of the first major users. This
technology allows prefeeds of shows and promos and commercials (yes even
PBS runs those now) to PC based video servers as MPEG 2 or 4 PES files
and is rapidly replacing videotape in syndication/newsfeed distribution.
Much cheaper to have the server capture a broadcast of a file than have
some master control operator have load and start videotape gear for a
scheduled feed in real time. And I understand that they back up the
satellite transmission of the IP streams with a broadband connection, so
if there is a dropout in some section of the transmission due to a burst
of uncorrectable errors the video server software can request that chunk
of the file over a net connection. Presumably Moviebeam system does
this by repeating the same feed over and over and handling errors by
filling in the holes with data from later feeds.
The viablity of the Moviebeam business model is left to others to
decide - and whether they have a secure protocol or not is as well (shame
on them if they don't don't in this day and age).
But it does provide a means of selling some otherwise unused bandwidth
(and maybe selling some otherwise useful bandwidth that might have been
dedicated to better quality video for PBS programming).
Dave Emery N1PRE, address@hidden DIE Consulting, Weston, Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in
celebration of what could have been, but wasn't and is not to be now either."