NABTS (the North American teletext standard) has 35 raw bytes per scan line. Typically, with some error-correcting redundancy bytes included, you get 28 usable payload bytes per scan line, 14-times the bandwidth you calculated below. This equates very roughly to one 9600 bps modem per scan line. The European teletext standard has more room for more bytes per scan line, since it uses a higher-frequency bit clock. ATVEF may or may not take advantage of that, however. -- Ben -- -----Original Message----- From: Chris Worley [mailto:cworley@xxxxxxxxxxxx] Sent: Wednesday, February 21, 2001 10:01 AM To: video4linux-list@xxxxxxxxxx Subject: Re: Strange data encoded in the signal from a PBS affiliate Peter Kaczowka wrote: > The other problem is the bandwidth of the analog ATVEF data. I think its > maximum is (please correct me if I'm wrong): > > 2 bytes per line * 11 lines * 60 fields per second = 1320 bytes / second = > 10.5 Kbits / second. ATVEF-A is only line 21, 2 characters on the odd field only (even field is XDS). So ATVEF-A is up to 2 * 30 bytes/sec. But, look at the data being transmitted (turn your teletext-2 capability on your TV during the midday gameshows, such as "Jeopardy" & "Family Feud"). They don't use the full bandwidth, and they assume a separate internet connection. The ATVEF-A is just a bit more than hyperlinks, timed with events in the show. I.e.: a question is asked, a hyperlink leads the settop box to fetch the possible answers and some javascript to keep score. For ATVEF-B and NABTS, your bandwidth analysis looks correct, but I believe the NABTS data contains up to 35 bytes per field, but I forget where I read that. Still, as you say, the bandwidth is nothing in comparison to what an mpeg stream can accomplish. Chris _______________________________________________ Video4linux-list mailing list Video4linux-list@xxxxxxxxxx https://listman.redhat.com/mailman/listinfo/video4linux-list
