[mythtv-users] scheduling not using all three tuners?

Max Barry mythtv at maxbarry.com
Tue Apr 11 23:53:42 UTC 2006

Peter Schachte wrote:
> The current pre-roll and post-roll are, I understand, intended to
> allow tuner cards to get ready to record. 

Right. Although personally I think this is a logical error. I won't
rehash the argument, already available here:


But to summarize, I believe hard buffers are for predictable time
shifting, while soft buffers are insurance against unpredictable time
shifting. A tuner card that always takes 20 seconds to initialize is
predictable, and should be compensated for with a hard buffer. It
doesn't make sense to use a soft buffer, which sometimes will capture
the time you need, and sometimes not.

Also, as you say, it would make more sense to use a per-tuner setting
for that purpose, not a global one.

But all this is moot, because I don't think pre-roll/post-roll is going
to change. (More on that later.)

> Here in Australia, the public stations tend to run pretty much on
> time, whereas you really need to end 10 minutes late if you want to
> record something on channel 10, so different *channels* need different
> start early and end late values, regardless of input or *program*. 

That would certainly be handy, although I'm wary about using the word
"need." If we are to get anything at all accepted into MythTV, we have
to find the shared ground between what the pro-soft-buffer people are
requesting and what the don't-mess-with-preroll people are refusing to
accept. So I think it's important to distinguish between what is a
necessity for us, and what would simply be handy.

A global soft buffer that does everything you want, but also
unnecessarily pads shows from the two reliable TV networks (ABC & SBS),
is still pretty great! It would be much better than the current
situation: a soft buffer that occasionally, unexpectedly vanishes when
consecutive shows are scheduled. (My patch simply fixed that precise
problem: it was never intended to redress more fundamental issues with

> So it seems to me the right thing is to have a pre-roll (and
> post-roll?) per *input*, and default start early and end late values
> per *channel*.

Makes sense to me.

> And when consecutive programs are to be recorded on
> the same channel and the same tuner, the pre- and post-roll can be
> ignored, and the start early and end late values shouldn't prevent
> consecutive programs from being recorded on the same tuner (though
> ideally the overlapping end late/start early time would be included in
> both recordings). 

That depends on what you mean by "shouldn't prevent." I certainly agree
that soft buffers should never create schedule conflicts.

But if you're saying that MythTV should prefer to drop the soft buffers
in order to record consecutive shows on the same channel *even if
another tuner card is idle*, I would disagree. That's the kind of thing
where users should be able to specify a preference. Some will prefer to
drop soft buffers in order to capture shows with their "best" tuner
card, or to keep a tuner card free for watching Live TV, or to save disk
space. But others (like me) won't. I don't believe a preference should
be hard-coded in.

Still, we're on the same page with this issue, and I like your ideas.

Now, importantly: my understanding is that any patch submission is
unlikely to be accepted if it alters the current pre-roll/post-roll
code. That is, we need to build a NEW soft buffer system that leaves the
current pre-roll/post-roll code untouched.

For this reason, I think we should stop talking about proposed changes
to "pre-roll" and "post-roll". We should instead talk about the new
system we're going to add.

You a coder, Peter? :)


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