I believe the standard you're referring to is ATVEF-A, see:
http://www.atvef.com/library/spec1_1a.html
The ATVEF-A data is on line 21 of the odd frames, along with the CC
data. It's teletext-2 format (so you can differentiate it from CC
data). Try watching some of the mid-afternoon gameshows like Jeopardy
where the CC and T2/ATVEF-A data are very heavily intertwined.
V4L2 needs a good CC/XDS API standard. I've got three routines I'm
successfully using to extract the data, but I haven't sent them to
Bill Dirks yet for approval.
When you say "bar code", I think you're talking about the line-21
signal. It begins with a clock pulse that has seven peaks. This is
followed by a start bit, seven data bits, a parity bit, seven more
data bits, and another parity bit (up to two 7-bit bytes of data per
frame). Watching line 21 (with an analyzer like a Tektronics VM700),
you should always see the clock, the start and the parity bits constant.
You also may be talking about ATVEF-B or NABTS (which is IP over
video). These use lines 10-20, but I don't know who's using them.
In either case, you need a hefty processor to do the DSP work in
nearly hard realtime (~2KBytes per scan line per frame to get 2 bytes
of data), or hardware that decodes the data for you. There are a lot
of decoders that do the CC/XDS for you, for example, the BT835 has a
fifo where you can read two bytes at a time across the I2C.
Chris
Sherm Pendley wrote:
On Tuesday, January 2, 2001, at 12:13 PM, Wandered Inn wrote:
Peter Lohmann wrote:
Eric Jorgensen wrote:
The data seemed to update a couple times a second, but didn't seem
to be entirely regular. Visually, it resembles a barcode.
So, I snapped a picture. Anybody know what this is?
Good thing you mentioned Arthur, since it made it easier to track down
the
likely culprit:
http://www.pbs.org/digitaltv/dataNS.html
I don't even want to know what they do with the Barney version.
Figures Microsoft would encode data in the viewable area. (Even if
most folks will never view it)
FWIW, this is the WebTV for Windows data -- program guide, etc. With
Win98 you can optionally install this if you have a compatible decoder
card (ATI All-in-Wonder, WinTV).
Following the link noted above, it indicates that it is used to interact
with M$ interactive toys (Barney, Arthur..) Doesn't say anything about
webtv.
Better late than never, so here goes... :-)
I work at WGBH Interactive, which produced and supported the server-side programming for the Barney and Arthur Actimates. I didn't personally program it, but the guy who did is two doors down the hall. I can tell you with reasonable authority that yes, the same encoding method is used to send that data as is used to send "enhanced" data to WebTV Plus.
The catch is, even though the low-level protocol used to encode the data for transmission within a broadcast signal is the same, the data format and application-level protocols are incompatible. It's sort of like how HTTP, SMTP, FTP, et al are different, even though at a lower level they all share the same transport mechanism - TCP/IP.
We use the same method, btw, to encode the web "markers" that you see on Nova. If you have a WebTV Plus, those are live links.
sherm--
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