[Bug 733819] Port teletextdec to 1.0

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=733819

--- Comment #10 from Daniel Kamil Kozar <dkk089 at gmail.com> ---
I've tried to find a solution to this before. However, there is one very
significant problem : there is no way of knowing where the clock appears. The
teletext spec (ETS 300 706) does not place any restrictions on the placement of
the clock, and different broadcasters put it in varying regions in the first
line of the page. All the transmissions in Poland have the clock on the right
side, but I've seen streams where the clock was placed on the left, or in the
centre of the header.
The most reasonable compromise, in my opinion, is to simply have the header
refreshed with every page that the decoder receives, while maintaining the body
of the page unmodified. However, this makes it look like the decoder is still
"searching" for the page, since the page number in the header changes as well.
Same as with the clock, the position of the page number is also up for the
broadcaster to choose.
However, analogue TVs were somehow capable of keeping the page number still
after decoding the requested page, while still updating the clock. I would
really like to know how this was done, as there is no data in the teletext
packets that would enable the decoder to update only the requested region of
the page header. This video shows this behaviour quite well :
https://www.youtube.com/watch?v=Xbyxi5j_22s
Anyhow, the current patch is based on the current git master, and updates the
page header with every page update. Let me know what you think.

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