[mythtv-users] picking channel to record show from

[Michael T. Dean]

*** Please do not read this message unless you first read all of Section 
12 of the HOWTO at http://www.mythtv.org/docs/mythtv-HOWTO-12.html .  
This message is not intended as a replacement for Section 12.  Anyone 
using information in this message to change their configuration without 
reading Section 12 assumes all responsibility for all effects of said 
change.

On 08/07/2009 03:33 PM, Matthew Zimmerman wrote:
> On Fri, Aug 7, 2009 at 12:37 PM, Michael T. Dean wrote:
>   
>> Matt, you probably don't want to increase the channel priority of the better
>> channel.  Read the above-mentioned section (12) of the HOWTO for why.
> Mike, I've seen you write that before, and I've read the section 12 of
> the HOWTO as you've suggested, but I haven't been able to determine
> why the best case in my scenario isn't to increase channel priority.
>
> About my setup, I have one antenna that's split into two cards.  One
> pchdtv-5500 and an air2pc card.  I have only one input defined.

On each card, I'm assuming.  Or, perhaps you meant to say, "Only one 
video source defined."

>   The
> pchdtv card does better than the air2pc card, so I have the input
> priorities set correctly.

Actually, to set it up properly, you'd have inputs defined with no 
(default) priority (therefore, set to 0) but you'd have them defined in 
the order of preference--with the pcHDTV card's input defined/created 
first.  To fix, you simply need to do the capture card portion of: 
http://www.gossamer-threads.com/lists/mythtv/users/264034#264034

>   I'm between Washington DC and Baltimore, so
> I get channels from both.  In my case for example, one CBS comes in
> better than another.  I use +1 for channel priorities and multiples of
> +5 for weighting the shows I prefer.

Per-recording rule priorities are fine and work as one would expect.

>   Doing this, I figure that a +1
> for a channel priority will ever override the selection of a certain
> show; it should only determine which channel to record that show on.
>
> Any insight, clarity, or suggestions you or anyone else have would be
> much appreciated.

But by increasing priority of an channel you're telling Myth, "I 
/really/ want you to record on this channel.  If you're using the only 
input with that channel and this show airs later, don't record the show 
I told you to record so you can record it later on my preferred input."  
Then, if the network decides to change the schedule and airs something 
else in the later timeslot, you may not get your good show.

Or, if you do, in fact, have one video source shared by inputs on both 
cards (meaning all channels are available on both inputs), you're 
saying, "I /really/ want you to record on this channel.  Even if the 
same episode airs earlier on a different channel, wait until the later 
showing on my preferred channel to record it."  Then, if at the time of 
the later showing, you have 2 other things scheduled to record, you may 
have a conflict.

By, instead, using a negative priority (-1) on the lesser-quality 
channel, you're getting a behavior more like what you want--to say, "I'd 
/rather/ have it recorded on the better channel, but don't skip 
recordings just to do it."

That said, though, in the real world, few people actually /ever/ want 
the effects introduced by setting input priorities.  These result in 
saying, "I'd rather you /not/ record this show than record from my bad 
input."  And, since simply defining the inputs in the order of 
preference is the only way to get the behavior most people want--"I'd 
/rather/ have it recorded from the first-defined input, but don't skip 
recordings just to do it."--I have not yet seen a good reason to set an 
input priority.  (And if someone did have a card so bad that they'd 
prefer to not record shows that they said they want to record rather 
than use that card, then why are they even defining the card in Myth?  
Why not just replace the card with a functional one?)

So, per-recording-rule priorities are fine.  Channel priorities (if done 
properly--generally, using negative priorities) aren't too bad.  Input 
priorities are almost always (or, IMHO, always) a Bad Thing (TM).

The big problem--and the reason most people who mess with channel and/or 
input priorities don't realize they have them improperly defined--is 
because the effects of improper usage only occur in certain situations 
and--unless they're closely watching the upcoming schedule and the 
listings themselves--they're likely to miss the fact that they missed 
something they wanted.  Or, when they do, they just chalk it up to, 
"Well, Myth is broken, so I'll send a message to the list saying, 'Weird 
Scheduling Behavior.'"  Or if they take the time to do some analysis of 
what happened they might use the subject, 'Myth Scheduler Has Serious 
Design Flaw' and then talk about how Myth should be written, not 
realizing that Myth did exactly what they told it to do (nor why it did 
what they asked it to do/how they asked it to do what it did).

Sure, you may not ever see the effect of having things improperly 
defined, but you should probably define things properly, anyway.  If you 
don't and you ever miss a recording because Myth decided not to record 
something you wanted it to record, please don't send a message to the 
list.  ;)

Again, (for anyone who read this far) please make sure you read (and 
take the time to understand) Section 12 of the HOWTO before making any 
changes to your configuration.  Complete information about MythTV's 
scheduling is in Section 12; whereas this message only provides a small 
subset of that information (and provides information directed toward a 
single specific system configuration).

Mike