[mythtv-users] Detecting / Recovering from HD channel broadcast changes?

[Todd Ignasiak]

On 4/5/07, R. G. Newbury <newbury at mandamus.org> wrote:
> Todd Ignasiak wrote:
> > Has anyone else run into this?  It happens infrequently enough that I
> > usually just fix it and forget it..
> >
> > Occasionally, my cable company changes the channel settings for my HD
> > (QAM256) stations.   Actually, I'm not sure if it's the cable company,
> > or the broadcast from the station .  But, some way or another, the
> > channel info (PIDs?) are changing, and MythTV cannot view/record them.
> >    After I notice a few missed recordings, I can go into mythtv-setup
> > and rescan the channel and it works again.  MythTV doesn't seem to be
> > as forgiving as some other devices to these changes.
> >
> > Has anyone else run into this, or found a good way to detect and/or
> > recover from it?
>
> I doubt that there is anything that can be done. The usual problem is
> that the cableco moves the program to a different frequency(channel)
> although the virtual channel may not change. It's especially bothersome
> when they are transmitting stripped QAM (where the stream identity info
> is NOT included). It may just be Rogers Cable, but I find that the PID's
> don't change when the frequency changes.

What I'm seeing on mine is they stay on the same QAM frequency, but
the PIDs within the broadcast change.  That's why I was thinking maybe
the changes are generated by the broadcaster, not necessarily the
cable company.

> > Maybe a polling script that compares the current info to the MythTV
> > settings & alerts you to changes could at least find the issue before
> > it causes failures.
>
> Would be nice, but I think you would need another box to check your box!
> I get over 450 digital streams. The check scan would have to parse the
> frequency, virtual channel and PID and compare that with the present
> database.
>
> Possible to do, but no such animal exists. And if you are working from
> stripped QAM, you still cannot tell *where* the channel has been moved
> to. You can guess, based on the PID, but that is *IT*. I have to watch
> the channels long enough to determine what they are...which is a real
> bitch when there are 6 or so CBC feeds all showing the same thing! And 8
> CTV feeds, and 6 Global feeds.

(Un)fortunately, most digital cable channels are encrypted for me, and
it seems like most U.S. viewers.  So, I only have a handful of
channels, making the job easier, although it could still be done with
a large number.     Since my channels are not changing, only the PIDs,
detecting changes is easier.  All of the channels I am using are OTA
broadcast channels, which include their PSIP data, so using that
information, detecting changes is even easier.      I might be able to
do it with a small shell script and the HDHomeRun command-line tools.


>
> > Or, is there already some way to get MythTV to alert me when a
> > recording fails?  As it is now, it just happily tries to record the
> > whole program, and the status says it is recording, but there is no
> > file output.     A more aggressive alerting/recovery mechanism would
> > be nice.
>
> Agreed, but I will dampen the fire by pointing out that I do most of my
> recording when I have gone to bed...I will *not* be there to see an
> alert. At best, I will see it the next day: too late to catch that
> error, but soon enough to fix it.

Maybe.  But, on the other hand, I could see running the scan a few
times per day, including during the workday, so when I get home I can
see the alert and re-scan the channel.  If a certain channel is a
frequent changer, maybe the re-scan could even be automated.


Judging by the small number of responses, maybe it's not a big enough
issue to worry about.