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. Matt
on 2006-06-02 19:32
on 2006-06-02 23:43
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 movies. 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 (eg stolen). 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, firstname.lastname@example.org 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."
on 2006-06-03 08:00
At 02:40 PM 6/2/2006, David I. Emery wrote: >On Fri, Jun 02, 2006 at 10:30:36AM -0700, Matt Ettus wrote: > 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. In some cities, the PBS broadcast in different formats at different times. For example, one Bay Area station starts broadcasting HD content at 8 p.m. till some late night time then switches to multiple SD content. So its possible that the MovieBeam data is distributed when the station is offering SD only. Since its all store and forward this should present no great problems. Steve