[mythtv-users] HD Homerun virtual tuners and cableco QAM channel remapping

lists.md301 lists.md301 at gmail.com
Tue Apr 3 13:36:16 UTC 2012

I finally had reason to try the Perl script (from the wiki) which queries
an HDHomerun Prime and obtains QAM channel mapping frequency and service
ID's.  My provider, Comcast, surprised me by making a change this past week
midweek.  Usually it's Sat night/Sun morning.  In the past when this has
happened, I've always edited the database channel tables manually (using
webwin), after making a list from the STB diagnostic screen for frequencies
and then guessing at the service/program ID's (which usually end up
unchanged), then restarting the backend.  This time, Comcast had done a
major re-order of the frequencies and ID mappings.  I modified the Perl
script to only report the changes, and the new dtv_multiplex lookups (which
are defined for a US-cable frequencies from scte65scan years ago), and then
manually entered the changes. Didn't trust the script to be writing to the
DB--but I guess this is something that will be more difficult down the road
when the developers get around to embedding the DB within the core app, and
thereby protecting the users from themselves.  I understand and applaud
this, but I hope there will be a way to update such changeable info
remotely, without having to do a full channel scan through the GUI and tear
everything up.  I started doing this years ago before any user interface
was mature, out of necessity.  I hope some kind of tie-in with a CC
Prime/HDHR QAM setup can be "built-in" when the times comes.  Yes, I know,
patches welcome. :)  But I digress.

My reason for writing this has to do with the consequence of Comcast's more
extensive remapping.  For each of my HDHR QAM tuners, I have 2 virtual
tuners defined.  I ran into something I never saw before, because they
switched the multiplex of several of the main HD network channels.  In the
old mapping, CBS and Fox were on the same transport, but now it's NBC and
Fox together (at least I think I have this right).  The consequence is that
the myth scheduler thought it could use one physical tuner to record a
simultaneous CBS/Fox shows, but obviously could not.  So in its confusion
it ended up recording the same tuned stream for both (I presume the last
one tuned), causing one to be missed.  Last Thursday I foobar-ed "Touch"
and "Person of Interest" this way.  I had fixed the DB assignments right
before they started recording, but didn't realize what was happening until
too late.  Also, after having changed the assignments, I did not restart
the backend because another recording was still going ("30 Rock" which
ended up being trashed for a clerical error, but I didn't know that at the
time).  I had assumed that maybe the scheduler didn't "see" the channel
mappings without a backend restart.  Of course, I never thought to do one,
until this past Monday night, where I also lost a new "House" episode,
sacrificed to the NCAA men's championship game, which did record
successfully.  I tried restarting the backend right after the recordings
started, and then re-activated the "House" recording, but the scheduler
didn't recognize the change.

I'm not sure this is a bug, per se, because this is a very special corner
case.  But I wanted to put it out there and ask if anyone else has seen it,
and if there are any steps I could take after a mapping change deal with
this situation.  I think the Perl script is a great thing, and I know the
author suggests that running it a 3am and letting it do an update
potentially keep you from losing recordings.  I'm thinking that if a user
has virtual tuners defined, it may have other issues.  Thoughts?  As I have
to finish my taxes (for myself and my mother) this week, intersecting with
myth not-recording time, I'm not sure how much time I'll have to experiment
with this in the coming week to get a handle on what's going on.
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