Bj|rn Remseth <rmz@ifi.uio.no> (06/07/91)
Does anyone know about existing hardware that puts a bitstream on a video channel and let you extract the same bitstream out of the video video signal, after it has been transmitted on standard video transport media such as satellite links, video cassettes and cable TV networks. This kind of equipment could use spare capacity on local cable networks and satellite sattelite links to spread e.g. usenet news quite inexpensively. But, the Big Question is: Does this hardware exist? Bj\o rn Remseth Institutt for Informatikk Net: rmz@ifi.uio.no Phone: +472 453466 Universitetet i Oslo, Norway Mail: rmz@neste.ifi.uio.no
clements@bbn.com (06/11/91)
In article <telecom11.439.7@eecs.nwu.edu> rmz@ifi.uio.no writes: > Does anyone know about existing hardware that puts a bitstream on a > video channel and let you extract the same bitstream out of the video > video signal, after it has been transmitted on standard video > transport media such as satellite links, video cassettes and cable TV > networks. > But, the Big Question is: Does this hardware exist? Devices exist to put compact-disc audio bit streams on videotape as "PCM" signals in NTSC format. Examples are the Sony PCM-501 and PCM-601. I have used them to record CD audio for storage and also to distribute it around the house on coax as a channel 3 video RF signal. This format has been used on the air in Boston to transmit audio from WGBH radio over WGBX TV (channel 44). How you get your data into the format of a CD player's digital output is a good question, though. Also, there are devices for recording on a VCR from a PC for backup. I assume (but haven't tried it) that the video signal that goes to the VCR could be shipped around by the video transport media you mention. I haven't actually used one of these things so I can't give you any better specifics. Check rec.audio for the former and the ibm-pc hardware group for the latter. Bob Clements, K1BC, clements@bbn.com [Moderator's Note: As mentioned a couple issues ago, a large number of REply messages on Hollings and other worn-out threads had to be dumped out unused in order to stay current with new items. If your REply message on an existing topic did not appear in this issue, you can pretty well assume it won't appear. This would apply to ACKS sent from here prior to 1 AM, 6-12-91. Thanks. PAT]
Ken Thompson <kthompso@donald.wichitaks.ncr.com> (06/14/91)
Closed captioning uses line 17 of the US TV standard to send text in serial packets. Ken Thompson N0ITL NCR Corp. 3718 N. Rock Road Wichita, Ks. 67226 (316)636-8783 Ken.Thompson@WichitaKs.ncr.com
jsd@proxima.uucp (Jeremy Druker) (06/15/91)
In <telecom11.439.7@eecs.nwu.edu>, rmz@ifi.uio.no (Bj|rn Remseth) wrote: > Does anyone know about existing hardware that puts a bitstream on a > video channel and let you extract the same bitstream out of the video > video signal, after it has been transmitted on standard video > transport media such as satellite links, video cassettes and cable TV > networks. > This kind of equipment could use spare capacity on local cable > networks and satellite sattelite links to spread e.g. usenet news > quite inexpensively. > But, the Big Question is: Does this hardware exist? Yep -- it sure does. The Magic Phrase is "Data Broadcast", and it works by sending data during the so-called Vertical Blanking Interval between picture frames. This is how teletext works, and data broadcast is, in fact, a specialized form of teletext. Ordinary teletext works by constantly retransmitting a set of pages of data, where each page comprises up to 25 rows of 40 characters each. Data broadcast, on the other hand, treats the transmitted data as a single continuous stream of bytes. There are one or two companies in the UK that I know of which suuply data broadcast receiving kit ("data decoders"). Only one as far as I know supplies the transmission ("head-end") kit, and that comprises a MicroVax with (hellish expensive) software that they wrote. The data decoder has an antenna socket and an RS-232 socket (or two for the fancy kind that can receive multiple channels simultaneously on different output ports). These cost in the region of 200 Pounds Sterling. In the UK, both BBC and ITV provide data broadcast capacity for sale (the horse racing betting shops use it to broadcast digitized audio commentaries of races, for instance) and in the US, PBS has been using data broadcast for some time too, though for what I don't know. I'm currently working on data broadcast head-end S/W myself (how else could I know all this trivia :-) but, alas, I do not own the rights to it :-( so I cannot publish any on the net. My system runs on a '386 under UNIX or Xenix, and with a DOS PC containing a PC Teletext broadcast card to convert the data to composite video format. The data rate is largely limited to what the data decoder can handle. For 625 line systems with 25 frames (50 fields) per second, the nett data rate is about 15Kbps per VBI line used; in our case we have chosen to use 8 VBI lines, which is as much as our data decoders can accomodate. I could go on and on and on (just say the word :-) but your eyes are surely glazing over by now. If you know of anybody who's interested in actually buying any of this stuff, mail me for names and numbers. Jeremy Druker jsd@proxima.UUCP !uunet!ddsw1!olsa99!proxima!jsd
bellutta@irst.it (Paolo Bellutta) (06/15/91)
rmz@ifi.uio.no (Bj|rn Remseth) asks: > Does anyone know about existing hardware that puts a bitstream on a > video channel and let you extract the same bitstream out of the video > video signal, after it has been transmitted on standard video > transport media such as satellite links, video cassettes and cable TV > networks. > This kind of equipment could use spare capacity on local cable > networks and satellite sattelite links to spread e.g. usenet news > quite inexpensively. > But, the Big Question is: Does this hardware exist? Yes. There are several ways to do that. Let's list the various kinds of media you can use: 1) VCR 2) terrestrial link 3) satellite link 1) can make use of the SMPTE/EBU time code, this is a digital code inserted in the VBI (vertical blanking interval), and represents hours:minutes:seconds:frames plus some spare bits you can use for special purposes. Since this is written on video tape, low bit rates can be achieved. In the US (but not in Europe) they have CC (close captioning) encoding which can be recorded on tape (always in the VBI). 2) can make use of the same code that is used for teletext and VPS codes. Since the channel bandwidth is a bit larger than in a VCR, a higher bit rate can be achieved. An alternative way is to use the NICAM encoding (used for terrestrial TV digital audio). 3) satellite transponders have a very high bandwidth, therefore subcarriers are used to carry additional data (for example different languages audio). Subcarriers can usefully encoded to transmit data at high bit rates. Adam Smith has a large production of Time Code HW. Rohde & Schwarz have DGF and DEF (coder and decoder) for VBI, DCA and DDA for digital audio. This covers 1) and 2). Sit on a chair before asking prices ;) Paolo Bellutta I.R.S.T. vox: +39 461 814417 loc. Pante' di Povo fax: +39 461 810851 38050 POVO (TN) e-mail: bellutta@irst.it ITALY bellutta@irst.uucp
Brian Litzinger <brian@apt.bungi.com> (06/19/91)
In <telecom11.439.7@eecs.nwu.edu>, rmz@ifi.uio.no (Bj|rn Remseth) wrote: > Does anyone know about existing hardware that puts a bitstream on a > video channel and let you extract the same bitstream out of the video > video signal, after it has been transmitted on standard video > transport media such as satellite links, video cassettes and cable TV > networks. > This kind of equipment could use spare capacity on local cable > networks and satellite sattelite links to spread e.g. usenet news > quite inexpensively. > But, the Big Question is: Does this hardware exist? I'm not entirely sure if this company has both ends or if the information is transmitted in a reliable manner, but you can certainly ask them such questions. TeleText Communications, (phone 1 408 735 8833) has at least a head-end which runs in a IBM PC Compatible. I've seen it operating on a local TV channel. Brian Litzinger @ APT Technology Inc., San Jose, CA brian@apt.bungi.com {apple,sun,pyramid}!daver!apt!brian
Jim Hickstein <jim.hickstein@icdwest.teradyne.com> (06/19/91)
Your mention of USEnet news brings to mind an outfit called "Stargate"
that did precisely this. Does anyone remember them? How dead is
"Stargate", anyway?
Data in the vertical interval on PBS is being used (one line) by a
company called InSight Telecast of Palo Alto, CA. (I am a former
employee.) It will (does?) carry program schedule information to
devices to be embedded in future VCRs that will provide an on-screen
version of the upcoming week. I believe the rate was to be about
9.6Kbps. There were a few people at PBS (or was it NPR?) who read
news; perhaps they can comment further on the technical aspects of the
VBI data equipment.
One factor in deciding to use PBS was that, compared to the big three
commercial TV networks, they had by far the most modern network.
Also, there was (is?) a legislated penetration of public TV into cable
markets that the big three's affiliates did not have. PBS had some
sort of venture to develop and sell this data service in the VBI,
which I personally question as being within the range of "public"
broadcasting.* I won't tell you how much they charged for a full-time
one-line slot, but it wasn't peanuts.
InSight Telecast was mentioned in a press release a few months back
which described their announced product. I don't have a reference
handy.
-----------
* Perhaps this is just another facet of the gradual commercialization
of non-commercial broadcasting in this country. I am revolted by the
"non-commercials" using up ten-second slots, with full video and voice
controlled by the "underwriter" (read: sponsor), at the beginning of
many programs. So far, they do not intrude into the *middle*, but
it's a slippery slope. I send them money -- quite a bit -- to escape
being targeted by commercial pitches. *sigh*