[mythtv-users] Detecting missed channels changes via logos

f-myth-users at media.mit.edu f-myth-users at media.mit.edu
Wed Nov 22 06:40:25 UTC 2006

    > 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)?

More information about the mythtv-users mailing list