[mythtv] Re: bilingual/SAP support (and Closed Captions)

Bela Lubkin filbo at armory.com
Sun Jul 18 00:51:14 EDT 2004

Originally sent: Sun, 11 Jul 2004 03:50:07 -0700

Stephane Zermatten wrote:

" I've been working on a patch for mythtv that makes it possible to record
" and watch bilingual broadcasts. The idea is to record both languages on
" the hard disk and then let users choose the language while they're
" watching. This works both when watching live tv as when watching
" recordings.
" Currently, this only works with PVR250/350 with an alpha version of the
" ivtv driver. That's why I'm not posting it as patch over CVS yet; I'm
" waiting for the new version of the driver to be released.
" In theory, it could be possible to support that with other cards and
" outputs (it won't work over PVR350 TV-out), but a PVR250 is all I have...
" Yet if someone is interested and is brave enough to install a
" development version of the ivtv driver to try it out, I'd love to
" have some feedback.
" This web page contains the patch over mythtv 0.15 and some usage
" information:
" http://www.geocities.com/szermatt/bilingual.html#step2

Greetings!  This work sounds interesting to me, but I have little
standing to speak: I do not yet run MythTV at all.  Still lurking,
trying to figure out what hardware to put together.

Nevertheless: I'd like to encourage you to continue with this work.
Please also make it easy to turn on both audio programs -- the
`test_ioctl -z 1` "(stereo): always play both channels, even if a
bilingual broadcast is detected" mode.  That is, please make the 'L'
toggle-SAP command cycle through all three (or even all four, adding
`test_ioctl -z 0` "(mono): play only one channel, whatever the real
broadcast mode is" to the cycle).

I've got a whole bunch of crazy reasons why this is a good idea.  First:
two listeners in the room want to hear different languages.  The brain
is pretty good at picking out what it understands (some years ago I
spent some time in Russia; despite understanding little Russian, I was
enjoy American shows they'd overdubbed, since they didn't actually erase
the English audio, just shouted over it).

Second: I always thought that I was probably subconsciously learning
Russian by doing this.

Third: external audio hardware separates the channels (e.g. to L & R
speakers) -- could easily be split into separate headphones or widely
separated speakers.


One reason I haven't leaped into MythTV yet is that I don't understand
its current state of Closed Caption support (and I saw some hints that
my choices of tuner hardware might affect that support).  One way I use
CC is to help me understand Spanish language broadcasts.  I understand
a fair amount of Spanish, but I still have trouble parsing fast speech
into separate words.  So I turn on CC and someone else does it for me.
If I had cable or satellite there are probably other languages I'd do
the same with.  [But if I had cable or satellite I'd spend so much time
watching junk, I'd never go outside... :-(]

I've seen some discussion of teletext(?) and DVB captioning, stuff like
that -- I don't understand the relationship between these things.  The
CC I'm interested in is the stuff that my TV (US, NTSC, standard
definition, receiving regular broadcast TV) will display when I toggle
"CC".  I understand it's encoded as a low-bitrate stream in one of the
overscan lines.

I hope to hear "oh yeah, MythTV records those and can either send them
to the TV as the same low-bitrate stream in one of the overscan lines,
_or_ optionally decode them to text itself, sending them to the TV as
overlaid graphics like the OSD".

Beyond simple passthrough or decoding of CC, I can think of all sorts of
interesting tweaks.  For instance, the captions in many programs lag
badly; it would be useful to have an adjustment to tell the decoder to
display them at some time offset from their actual location in the
stream.  That would be impossible with real live TV on a hardwired TV
set; it becomes possible when you're watching a recorded stream.
(Similarly, sometimes the audio and video are out of sync _as broadcast_
by the clowns at your local station -- it would also be useful to have
manual control over the time skew between audio and video.)

Another nice (and simple) tweak would be "fold to lowercase" -- most CC
is all-uppercase, a bit annoying to read.

OK, I'll go back to lurking now.  Argh.  I wish I'd discovered MythTV
about 2 months earlier, I'd probably have a box working in time for the
Olympics instead of still trying to decide on a hardware platform...



The above is a repost of my first ever posting to the MythTV mailing
lists, which was trapped because I wasn't a list member:

" Your mail to 'mythtv-dev' with the subject
"     Re: bilingual/SAP support (and Closed Captions)
" Is being held until the list moderator can review it for approval.
" The reason it is being held:
"     Post by non-member to a members-only list
" Either the message will get posted to the list, or you will receive
" notification of the moderator's decision.  If you would like to cancel
" this posting, please visit the following URL:
"     http://mythtv.org/cgi-bin/mailman/confirm/mythtv-dev/68e32b96c9e06f50b0=
" 4ce4eaeac015e70cfe7c8b

I waited a week.  After receiving neither a moderator's negative
decision nor a copy of my message in the archives, I've reposted it.
Hopefully it will now pass since I am now a list member.


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