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

Steve Hodge stevehodge at gmail.com
Sun Jul 30 02:47:07 UTC 2006


On 7/30/06, chris at cpr.homelinux.net <chris at cpr.homelinux.net> wrote:
> On Sat, Jul 29, 2006 at 07:56:01PM +1200, Steve Hodge wrote:

> As I understand the argument, the scenario is as follows:
>
> pre/post padding: 2 minutes
> show 1: 1700-1730, channel 38, priority 5
> show 2: 1700-1730, channel 40, priority 1
> show 3: 1730-1800, channel 51, priority 5
> show 4: 1730-1800, channel 38, priority 1
> tuner 1: high quality
> tuner 2: low quality

Ok, I see. But do recording priorities actually guarantee that the
higher quality tuner will be used? My understanding is that they
don't, they just advise the scheduler to try to fit those shows first.
If that's how it works then I don't see a real issue here. Show 1 gets
scheduled on tuner 1, show 3 gets scheduled on tuner 2 (as it cannot
be recorded by 1), now show 4 can also be recorded on tuner 1. Show 2
is a conflict. This solution is ideal AFAICS (without the complication
of dropping padding, which is a separate issue IMHO). If the
priorities were switched then 1 and 4 would end up on tuner 2 and you
could argue in that case that the tuners should be switched around to
maximise the use of the higher quality tuner.

But you're still getting more recordings that you can get from MythTV
right now so the proposed implementation is still a clear improvement.
Is Michael (or are you) suggesting that no improvement should be made
unless if solves all cases perfectly?

> The issue is what to do between 1728 and 1732 when the channel 38
> switches from the higher priority recording to the lower priority
> recording.  Do we force channel 38 to stay on one tuner for the
> whole hour so that we can duplicate the 4 minutes of overlap and
> create two monolithic recordings?  If so, which tuner do we use?

Yes we keep on tuner on channel 38, and I'd say that it would be
better to use tuner 1 to maximise the use of the higher quality tuner,
but as the priorities for shows 1 and 3 are identical so the user has
not expressed a preference and it would not be wrong to use tuner 2
for channel 38 either.

> Would the answer be different if the shows had different priorities
> favouring one half hour or the other? What if we had a rediculous
> number of sequential shows on channel 38?

Highest priority show gets scheduled first. It gets the highest
priorty tuner. Any other lower priority adjacent shows on that channel
also use that tuner.

> The simple solution is to say "this is too complicated" and post a
> conflict.  Shows #2 and #4 both get dropped.  Show #1 gets tuner #1
> and show #2 gets tuner #2 and both record for the full 34 minutes.

That is the current behaviour, yes?

> A slightly more enlightened solution says "I can't give you the
> pre/post padding, but if none of these shows can be rescheduled
> then I'll do a hard swap between the tuners at 1732."  (I chose the
> late switch on the assumption that it's better to miss the start of
> a show than the end of a show.)

I think that recording partial shows where possible in the case of
conflicts like this would be a desirable enhancement. However it's not
the one we're talking about.

> Another variation would be to truncate show #2 so that #3 can be
> recorded in its entirety on tuner #2 (the question is whether a
> complete show is better than a high-quality show or vice-versa), in
> which case tuner #1 doesn't switch and the feed can be duplicated
> from 1728 through 1732 so that show #4 has a pre-pad.  Everybody
> wins here except show #2.

This is what I'd like to happen, either with the truncating of show 2,
or more simply with recording show 2 at all.

> A *REALLY* fuzzy solution would split tuner #1 at 1728 and then
> swap tuners at 1731.  The 3-minute fragment from tuner #1 would
> then be transcoded to match the output of tuner #2 and the parts
> that make up show #4 assembled during post-processing.  In this
> case, Shows #1 and #4 are complete, show #2 loses half the
> post-pad, and show #3 starts a minute late.

I think that's overly complex, and certainly beyond what we are
talking about here.

> > Again, that's not the implementation most people here are talking
> > about. We are talking about a single tuner writing two adjacent
> > recordings to two files and including the overlap in both files.
>
> That's what *you* are talking about.

Right, and I still haven't heard a convincing argument against this
specific improvement.

> Dean (?) is saying that
> although your simple example has a simple solution, that solution
> doesn't scale.  The more constraints you put on a situation ("two
> shows on the same channel on the same tuner") the less practical
> the solution becomes.

But it's still an improvement over current behaviour and it's not a
complicated solution (unlike the proposal to record shows with
different tuners, and combine them in post processing). I still don't
see a fundamental objection, just repetition of "it won't scale"
without a concrete example of how it won't scale, and an attitude that
the current behaviour is perfect (I'm not refering to you
specifically, just the impression I get from a couple of the posters
in this thread).

Steve


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