[mythtvnz] Overlapped recordings on ivtv cards?

[Dr. David J. Knowles]

Nick Rout wrote:
> On Mon, Nov 23, 2009 at 3:48 PM, Steve Hodge <stevehodge at gmail.com> wrote:
>   
>> On Mon, Nov 23, 2009 at 10:56 AM, Dr. David J. Knowles
>> <dknowles at clearfield.com> wrote:
>>     
>>> Soft padding is a global setting (set in Setup->TV
>>> Settings->General->Advanced).
>>> In this page you can set before recording time and after recording time
>>> values. Soft padding
>>> is added onto all programs recorded IF POSSIBLE. If the padding is not
>>> possible it is ignored.
>>> One example of soft padding being ignored is for adjacent recordings.
>>> Adjacent recordings
>>> stop at the moment the scheduled program ends. This leads to the problems
>>> with the end
>>> of programs appearing on the next recording.
>>>       
>> My understanding (and I may be out-of-date so please correct me if I'm
>> wrong) is that soft padding is applied after the schedule is determined.
>> This means that if you use soft padding and have two tuners capable of
>> recording the two adjacent shows then the padding will not be applied and
>> the shows will both be recorded on the same tuner. This is less than ideal,
>> particularly for people who have say analogue Sky on one tuner and then DVB
>> multirec on another - the soft padding will be lost on shows on Freeview
>> unnecessarily.
>>
>> If Mythbusters is the only case where this issue is coming up frequently,
>> just let it record another showing: both the current season and the earlier
>> season repeats are shown multiple times per week.
>>
>> It'd be great if the scheduler were able to handle padding better.
>> Unfortunately it's not as simple as it first seems and the scheduler itself
>> is a complicated piece of code. That's why multirec is implemented the way
>> it is - having "virtual tuners" may be a bit of a hack (with its unnecessary
>> requirement of pre-determining how many you might need), but it meant it
>> could be implemented without a lot of changes to the scheduler. I believe
>> there's been one aborted attempt to get the scheduler handling padding
>> better, so I suspect it'll be a while before anyone tries again.
>>     
>
> I guess it would theoretically possible to back-to-back on same
> analogue channel by writing the stream during the overlap period to
> two files. Kind of like the tee command works in a shell. However this
> could only work on the SAME channel and would obviously involve a lot
> of coding.
>
> Ironically the analogue codebase may get some serious attention as the
> result of the US switching over. For many US users the only way to use
> myth is via an analogue encoder plugged into a STB.
>
>   
I tracked an almost identical bug in the mythtv bug tracker for a long 
time. My understanding was that the scheduling is handled in one place 
in the code and the actual recording is run on another. This allows 
multiple systems all capable of recording to be stitched together under 
the auspices of a single master server. It does however makes the 
allocation of this overlap very complex especially when some of the more 
arcane rules (selective reallocation based on priority etc) are brought 
into the mix. Multirec was introduced as the solution to this bug and it 
cheats by using multiple virtual tuners on one card.

Soft padding is a global setting and as has previously been mentioned is 
added selectively if possible. Hard padding is a property of the 
recording rule. This means that it can be overridden for the programs 
you are trying to join together (as it were). There is a default hard 
padding setting which can be set as the default for rules. So new 
recording rules get the hard padding values if not overridden.

------------------------------------------------------------------------
Dr. David J. Knowles  <dknowles at clearfield.com> Senior Systems Architect
Phone (+64 9)  358 2081                          Clearfield Software Ltd
Fax   (+64 9)  358 2083                    1st Floor 8-10 Whitaker Place
Mob   (+64 21) 75 9090                P O Box 3901 Auckland, New Zealand
------------------------------------------------------------------------



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