[mythtv] Closed Captioning & Teletext/Videotext

Erik Arendse erik_nospam.arendse at bigfoot.com
Mon Jan 20 08:49:25 EST 2003


At 17-1-03 17:09, Henk Poley wrote:
> > Van: Erik Arendse <erik_nospam.arendse at bigfoot.com>
> >> Uh, how are you going to sync subtitles (?Closed Captioning?) then?
> > Close Captioning is separate from the rest of my engine, it's just that
> > as I included the teletext decoder it  will be only so much work to show
> > all pages. Not fully implemented yet, but it will be.
>So you "magicaly" know what Teletext page is used for CC? I know that
>most channels use page 888, but not all. I seem te remember channels that
>use _different_ pages for different programs.
I just store all pages mark as "subtitle", on playback the user can select 
the page to view. This adds some unneeded program info to the data (I think 
891-895 on our national nets) but avoids setting up which pages to grab for 
each channel to be watched. For some channels this has the benefit of 
storing 5 or 6 different subtitles at the same time, user-selectable on 
playback.
On playback you can choose (using a single toggle key probably) which page 
you can view from all available pages the playclass has seen for the show 
played up to that point.

> > CC is added to the recorded file in a new type of CC-frame, it's only a
> > few lines every few seconds.
>
>It could even be witten as an MPEG4 Closed Captioning stream, when
>recording with DivX. AFAIK, MPEG4 has standardized subtitles, isn't it?
I will not support that myself. Isaac has created a rather nice fileformat 
which can transparently support whatever decoder you want, I'm not hacking 
into any specific video format. If anybody wants that, its place should be 
a Divx export module for MythTV.

> > Adding Teletext to the recorded file would be a
> > load of data for no use (why would anyone read shifted or recorded
> > teletext?)
>Doing just a "streamed" diff would slowdown the playback (fast-forward,
>rewind) process, isn't it?
You lost me there...
'When' do you want to diff 'what' with 'what'?

Erik



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