[mythtv-users] Live TV channel restrictions

[Michael T. Dean]

On 02/24/2010 04:46 AM, Tortise wrote:
> From: "Ian Oliver"
>> Michael T. Dean wrote:
>>> If you always want LiveTV to get a separate physical
>>> tuner
>> That isn't what I want. If there is a tuner on the right mux and with 
>> a free virtual tuner, then use it. Failing that, find a free tuner 
>> and tune it to the right mux.

That's the default configuration of MythTV.  The part you're complaining 
about is that you're then "stuck" on the mux.  To fix that, enable 
"Browse all channels."

>> Failing that, tell me I can't watch that channel. All PVRs I've met 
>> do pretty much exactly this

/me wonders just how many PVR's you've seen that support recording from 
X virtual tuners on each of Y physical capture cards

I can turn your MythTV system into something just as "simple to use and 
always works like I expect" as a dual-tuner TiVo.  That's an easy 
problem.  :)

> I think this "if" logic is flawed.  (I assume LiveTV needs a free 
> dedicated tuner, not a shared Tuner, it should first hunt for a free 
> tuner.  An assumption here is that the code is not setup to directly 
> jump tuners to use a tuner which is already pulling a mux, when there 
> remain free virtual tuners on the tuner.)
>
> I suggest a useful perspective is that LiveTV is a different beast to 
> a recording mux and they merit recognition of their differences in 
> their treatment.
>
> A LiveTV Tuner is ideally locked to one tuner - why - because a Live 
> user may want to choose any channel from any mux anytime.
>
> A Rec Tuner is distinguished by not having an enduser who is going to 
> demand the tuner change any time to any mux.
>
> These distinctions seem fundamental to me.
>
> So, from a different perspective, what is an ideal number of tuners?  
> That depends.  The most efficient number of tuners one should ever 
> want should be {[number of mux] + [number of LiveTV viewers]}
>
> [number of LiveTV viewers] deserves further clarification, that is not 
> the number of frontends, rather it is the maximum number simultaneous 
> Frontend viewers likely or perhaps possible.  So in a house with 6 
> frontends but only 3 people present 3 is likely to be enough for 
> [number of LiveTV viewers].
>
> To highlight that the current mythtv setup is a problem, consider we 
> have 3 muxs here, I have 4 (multirec) tuners (T0, T1, T2 and T3) and I 
> have enabled LiveTV selecting a free Tuner.  (I forget the exact 
> phrase)   Multirec recordings start at T0 and work their way up, T0, 
> T1, T2 - and that is all that's needed for all combination of 
> recordings, so long as there is no demand for channels > 5 on any 
> mux.   A LiveTV session ("LiveTV1") is opened on a frontend and mythtv 
> selects T3.  All good.
>
> Now a second frontend LiveTV session ("LiveTV2") is started on a 
> second frontend - and that is when it falls apart because LiveTV2 also 
> gets T3 - and suddenly the problem is back again as one tuner 
> dominates controlling the mux and effectively limiting the channel 
> options available to those on that mux (therefore for LiveTV1 and 
> LiveTV2).  Manually swapping Tuners works for the technically savvy - 
> mostly I find T2 is free, however mythtv should really have put 
> LiveTV2 user onto T2, assuming it to be free, which mostly it will 
> be.  I've not tested a 5th tuner however I expect the situation would 
> be the same, LiveTV1 gets T4 as would LiveTV2 also get T4.   T3 would 
> remain lonely, would it not?   (reservation: I've not managed to get 
> my head around how this might work if Mike Dean's "Revolving" next 
> Virtual Tuner assignment method might impact on this and experience 
> suggests I'd be best to configure it and test to comment on it however 
> Mike might be able to comment on its impact in the scenario I portrait)

This is exactly what the post I linked allows the user to configure.  
You can configure MythTV so that it either always re-uses a physical 
card (meaning you're stuck on the mux unless you a) hit NEXTCARD, b) use 
the EPG, or c) enable "Browse all channels")--this being the default 
configuration--or can configure it so that MythTV always grabs a 
different physical tuner for each Live TV session (assuming one is 
available, or if not, grabs a virtual tuner already "stuck" on a mux due 
to some other recording or Live TV session)--this being the 
configuration where you tell MythTV that Live TV is important to you.  
Note that in the second case, you get exactly what you seem to want--a 
separate physical capture card for each LiveTV session.

> Regarding the more than 5 virtual tuner limit, the useful limits here 
> seem to be hardware based and therefore quite variable, depending on 
> the individual servers capabilities, mainly its effective pipe size to 
> the HDD(s).

Really, it's a scalability issue.  On any given hardware, scheduling 
becomes a much harder (and, therefore, much slower) process as the 
number of virtual tuners grows.  It's not the absolute time required for 
scheduling that caused the devs who implemented multirec to choose a 
limit of 5 virtual tuners (as the absolute time /would/ be hardware 
specific), it's the difference in scheduling time required between 5 and 
6 (and 7 and 8 and ...) virtual tuners.  Graph it and you'll see a 
non-linear growth.

Mike