[mythtv-users] Detecting missed channels changes via logos

[f-myth-users at media.mit.edu]

    > Date: Tue, 21 Nov 2006 10:34:31 -0500
    > From: Daniel Kristjansson <danielk at cuymedia.net>

    > On Tue, 2006-11-21 at 08:26 -0600, Kevin Kuphal wrote:
    > > Brad DerManouelian wrote:
    > > > On Nov 20, 2006, at 8:03 PM, f-myth-users at media.mit.edu wrote:
    > > > I like the idea, but instead of logo detection, it should read the  
    > > > metadata that comes down from the stream to make sure you're actually  
    > > > recording the correct show. The metadata won't always match the show  
    > > > title perfectly, so it should be liberal with what it considers to be  
    > > > the "correct" show. Does anyone know off the top of their head if  
    > > > this data comes down for most channels now? Maybe it's just something  
    > > > that comes on channels with closed captioning?
    > > >
    > > >   
    > > You can pass "-v xds" into mythbackend as a command-line option and it 
    > > should print out all the XDS data that it finds.  I believe this was 
    > > included in 0.20

    > I believe it is "-v vbi" and this prints all VBI information we parse,
    > including XDS.

In 0.18.1, at least, all I see is
  Can't enable VBI recording
  VBI service: 4, packetsize: 0, io size: 0
even though I'm getting correct closed-captioning data from my flock
of PVR-250s. (ivtv 0.4.0/0.4.1)  Should I be seeing more?  (I've been
using "-v all" since I installed Myth.)  I'm guessing from the comments
above that logging in this area has been expanded in 0.19/0.29/SVN, but
I haven't checked the code.

I -did- speculate about using this metadata in the PS to my first
message, and if it worked it'd be great, but I have some doubts about it:
(a) I'm pretty sure that normal analog channels -do- transmit their
    callsigns (and maybe other things) because I've seen some VCRs
    display callsigns in their OSDs.  I dunno if -all- broadcasters
    provide this data, but many do, at least on my particular cable
    service (no idea re broadcast).  But:
(b) I have no idea how common this is in the analog output of STBs.
    After all, tuning broadcast analog or cable analog -isn't- an
    issue, because tuner cards don't miss channel changes.  STBs,
    on the other hand, are the prime suspects in missed changes,
    and I don't know how how commonly they embed anything useful
    in their analog outputs that might indicate what channel they
    think they're tuned to.
(c) I know nothing about the metadata in digital sources (e.g., HD,
    or Firewire-anything, etc etc).

So unless STBs routinely embed XDS/VBI data, looking for the metadata
might only help us in the one case that always works, namely data
coming in from an analog-source capture card---their tuners don't need
blasters and don't mistune... :)

On the other hand, if image data isn't coming in, the user will attend
to -that- little detail pronto, so we can pretty much assume it'll be
there. :)

Does anyone know what the answer to (b) is likely to be?  (Yes,
there's lots of different hardware, but which way does it trend?)
How about (c)?