[mythtv-users] Input priority

Michael T. Dean mtdean at thirdcontact.com
Thu Jan 21 05:02:28 UTC 2010


On 01/20/2010 07:44 PM, Robin Gilks wrote:
>> I have 2 backends with 2 capture cards each (and /only/ local storage).
>> When I created capture cards, I created those on the master backend
>> first, then the two on the remote backend last.  However, I connected
>> inputs on card 1, then 3, then 4, then 2.  Therefore, my system's
>> backend status page shows Encoder 1 through 4 in order, but it will
>> record first using encoder 1, then 3, then 4, then 2.  All my capture
>> cards are the same, so the reason I chose the order is to load-balance
>> my storage.  (Encoder 1 is always used first, so the MBE does the first
>> recording, but since additional encoders are only used when recording
>> multiple simultaneous recordings, I connected 3 and 4 to pick up the
>> next-most-frequent usage, then 2 for the least-frequent usage.)  I could
>> have added cards in any order (so I could add them in the same order as
>> I connected inputs), but I like having them organized by backend on my
>> status page, rather than by order of preference.
>>
>> If you have set input preferences, the best way to ensure you go back to
>> a known state is the Delete all capture cards approach.
>>     
> Does this mean what I think it does?
>  * no display tells you the actual order - you have to remember how you
> configured it
>   

That's probably true.  On the bright side, the best way to set things up
is to always start with "Delete all capture cards" and then re-add cards
and inputs, so you don't have to remember for very long.

And, if you happen to create capture cards in the same order as you
connect inputs, it definitely makes it easier to remember--and then the
backend status page will also show you the order.  :)

>  * on your example, LiveTV always starts on card 2, that being the
> 'lowest' priority by order, not on the highest numbered card
>   

No, LiveTV would normally start on the lowest-numbered local card. 
However, with the setting:

Avoid conflicts between live TV and scheduled shows
If enabled, live TV will choose a tuner card that is less likely to have
scheduled recordings rather than the best card available.

enabled, it does the opposite--it starts on the highest-numbered card
(and no longer prefers local cards).

Note that means LiveTV uses card order, /not/ input order (for various
not-so-interesting reasons--most of which I don't know).  So, on my
setup (since I have "Avoid conflicts..." enabled), it starts on card 4,
then 3, then 2, then 1.

If I disabled "Avoid conflicts...", it would start on card 1, then 2,
then 3, then 4.

And, regardless of the setting for "Avoid conflicts..." recordings on my
system start on card 1 (input 1), card 3 (input 2), card 4 (input 3),
card 2 (input 4)--*because* all my inputs have equal priority (0, the
default, which is what 99.999% of all cards should have).

So, if I used LiveTV, the card order would be important--and, would,
therefore, affect my decision for the order to create cards.

Since people who use LiveTV probably want cards/inputs used in the exact
same order as they're used for recordings or the exact opposite order
(depending on the value of "Avoid conflicts..."), they should probably
create cards in the same order they connect inputs (in the order of the
most-preferred to least-preferred input).

However, since LiveTV uses a different criterion for order of usage, you
can actually use this to your advantage when setting things up to give
you full control over the exact order things are used for both LiveTV
and recordings.  (Now that you understand the details.  :)

>  * the input preference is useless, does nothing and is depreciated
>
> I have 3 cards - a PVR150 on an STB and 2 DVB cards. The PVR150 is input 1
> (is that the same as card 1?) with priority 1 and the DVB cards are inputs
> 2-5 and 6-9 with preference +5. Recordings for me have always used the DVB
> cards first - you're saying they *SHOULD* be from the PVR150.
>
> Very confused from NZ...
>   

No, I'm saying that making the DVB cards +4 makes any show that can be
received on them 4-higher priority than any show that can be received on
the PVR-150.  So, if you have 3 shows to record and you could record all
3 using the inputs you have, but the show that would end up recording on
the PVR-150--we'll say it's LOST, your 3rd favorite show in the
world--happens to re-air later at a time when a DVB card is not busy,
Myth will probably record the #1 and #2 shows using the DVB cards and
leave the PVR-150 unused, deciding instead to record the later showing
of LOST just so it can use a DVB card.  Then, at the time when the
episode of LOST was supposed to re-air, it turns out that the network
decided to broadcast something else, so that LOST episode is no longer
on the schedule, meaning you never record it.

/If/ all inputs have equal priority, they are used in input order.  If
not, the priority will affect order of input usage, but--as stated
above--it also affects which shows are recorded and which airing of
shows is recorded, which affects whether shows are recorded.

Add to this channel priorities, and things get complex really quickly. 
IMHO, except in very rare circumstances, no one should ever use any
priorities other than per-recording rule priorities (or custom
priorities that affect specific shows).

Or, more succinctly, input priorities are evil and channel priorities
are generally bad.

If you're using priorities for inputs or channels, you most likely want
to use negative priorities for the bad ones rather than positive
priorities for the good ones.  But, don't do that unless you read and
fully understand section 12 of the HOWTO... 
http://www.mythtv.org/docs/mythtv-HOWTO-12.html

Mike


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