[mythtv-users] is mythtv smart enough to do this (overlap/back-to-back) with recordings?

[Peter Schachte]

On Sat, Jul 29, 2006 at 02:39:09AM -0400, Michael T. Dean wrote:
> http://www.gossamer-threads.com/lists/mythtv/dev/195124#195124 (all 4 
> pages of the thread)

OK, I reread the thread and still find it raises more questions than
it answers.  There is some discussion of algorithms for scheduling,
but little discussion of how to decide which is the best recording
schedule for a certain TV schedule and set of desired recordings and
available tuners with their respective priorities.  This is really
just an optimization problem, and without a definition of the
objective function (http://en.wikipedia.org/wiki/Objective_function)
to be optimized, how can you tell whether or not your scheduling
algorithm is correct?  And once you do define the objective function,
there are many optimization algorithms that can be used.  So is the
intended objective function explicitly defined (perhaps informally)
somewhere?

When you look at it as an optimization problem, any change to myth
that allows new possible schedulings without removing any old possible
schedulings, such as allowing multiple recordings to be written from a
single tuner card at once, must be a good thing.

Your key point against allowing multiple recordings to be written from
a single tuner card at once seems to be that it will surprise and
confuse users.  They won't be able to predict or understand how the
scheduler will schedule things.  I believe the best way to ensure
myth's scheduler is understandable and that users can achieve what
they want is to explain the objective function and what schedules are
possible (such as the maximum number of simultaneous recordings on a
single tuner from a single channel or transport, and whether or not
myth can switch tuners in the middle of recording).

Your second, more technical argument is that right now Myth always
records higher priority programs on the highest priority tuner
available.  If overlapping back-to-back recordings on the same channel
(or transport) can be recorded on a single tuner, this could cause
problems if the back-to-back programs have different priorities and
there are competing high priority programs.  This just means that you
need to decide which is more important:  recording the lower priority
program at all or recording higher priority programs on higher
priority tuners.  Again this is a question of the objective function.
Maybe the right thing is to let the user make the policy decision,
similar to what she now does with the "reschedule higher priority
programs" setting.  In any case, this hardly seems like a damning
example, nor the kind of problem that is unique to the feature being
discussed in this thread.

-- 
Peter Schachte              There is no logical end to the application of
schachte at cs.mu.OZ.AU        economic rationalist principles.
www.cs.mu.oz.au/~schachte/      -- Jim Davidson 
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