Mailing List Archive: MythTV: Users

Back-toBack recordings from the same source

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pieter at insync

Apr 24, 2012, 3:58 PM

Post #1 of 3 (256 views)
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Back-toBack recordings from the same source

Hello List,

This might be a dev list question, but here goes:

Is there a way to tell Mythtv to use the same source for back-to-back
recordings of programs, with overlapping start and finish times ? (what
a mouth full :) )

Let see how my ASCII art skills are:

------>time

--->(1)--->(2)--->(3)-->(4)--->(5)--->

1) Start of "P1" recording
2) Real start of "P1"
3) Start of "P2" recording
4) End of "P1"/Start of "P2" following 1 or two ads (In New Zealand,
zero ads between programs on some channels, there is title scrolling and
all that)
5) End of "P1" recording
--> Live goes on

I have found it *very* hard to get the over-recording right (I think
they call it "island time" :D ). The best way for me is to set the
pre-start recording time to 120 seconds and over record by 300 seconds.
The problem this causes is that "all" my tuners are busy (hauppauge Nova
S Plus)

I am told this card can do up to 8 recordings (via that magic that Myth
does) but I could have sworn the last time I set it to 8 the quality
went down (the picture appeared snowy) If the card is happy to handle 8
decodes, then that solves my problem, but what about people that arn't
that lucky.

Here is what I thought could happen:

At 3) - create another ring buffer that "feeds off" the already created
ring buffer for 1)
At 4) - release the ring buffer for 1)
At 5) - release the ring buffer created at 3)

I hope that makes sense, comments/flaming welcome

Cheers,

Pieter
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dekarl at spaetfruehstuecken

Apr 25, 2012, 1:44 PM

Post #2 of 3 (231 views)
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Re: Back-toBack recordings from the same source [In reply to]

On 25.04.2012 00:58, Pieter De Wit wrote:
>
> Is there a way to tell Mythtv to use the same source for back-to-back
> recordings of programs, with overlapping start and finish times ? (what
> a mouth full :) )

You can record overlapping programs from one DVB card with the multirec
feature. By default each DVB cards gets added as 2 virtual tuners.
You can push that up to 5 in mythtv-setup.

> Let see how my ASCII art skills are:
>
>
> ------>time
>
> --->(1)--->(2)--->(3)-->(4)--->(5)--->
>
> 1) Start of "P1" recording
> 2) Real start of "P1"
> 3) Start of "P2" recording
> 4) End of "P1"/Start of "P2" following 1 or two ads (In New Zealand,
> zero ads between programs on some channels, there is title scrolling and
> all that)
> 5) End of "P1" recording
> --> Live goes on
>
> I have found it *very* hard to get the over-recording right (I think
> they call it "island time" :D ). The best way for me is to set the
> pre-start recording time to 120 seconds and over record by 300 seconds.
> The problem this causes is that "all" my tuners are busy (hauppauge Nova
> S Plus)

I run everything with 5 minutes start-early and end-late as default/in
each recording rule. (MythTV has start-early/end-late and pre-/postroll
which are two different things. the former is enforced but the latter
is not due to different use cases)
For some programs I have end-late set to 45 minutes, works very well,
too.

> I am told this card can do up to 8 recordings (via that magic that Myth
> does) but I could have sworn the last time I set it to 8 the quality
> went down (the picture appeared snowy) If the card is happy to handle 8
> decodes, then that solves my problem, but what about people that arn't
> that lucky.

The card should just be pumping bits and not be decoding any streams.
The restriction is likely on the number of different PIDs/streams that
the card can filter out in hardware.
And the GUI setup will only allow you to configure 5 parallel
recordings.

> Here is what I thought could happen:
>
> At 3) - create another ring buffer that "feeds off" the already created
> ring buffer for 1)
> At 4) - release the ring buffer for 1)
> At 5) - release the ring buffer created at 3)

Rewriting the backend to allow overlapping recordings on all card types
or hiding the virtual tuners in a generic 1xMPTS -> NxSPTS filter is
certainly possible and a nice idea, but it will likely require a very
low level rewrite of much recording and scheduler code for little gain.

Regards,
Karl
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nick.rout at gmail

May 3, 2012, 1:21 AM

Post #3 of 3 (199 views)
Permalink

Re: Back-toBack recordings from the same source [In reply to]

On Wed, Apr 25, 2012 at 10:58 AM, Pieter De Wit <pieter [at] insync> wrote:
> Hello List,
>
> This might be a dev list question, but here goes:
>
> Is there a way to tell Mythtv to use the same source for back-to-back
> recordings of programs, with overlapping start and finish times ? (what a
> mouth full :) )
>
> Let see how my ASCII art skills are:
>
>
> ------>time
>
> --->(1)--->(2)--->(3)-->(4)--->(5)--->
>
> 1) Start of "P1" recording
> 2) Real start of "P1"
> 3) Start of "P2" recording
> 4) End of "P1"/Start of "P2" following 1 or two ads (In New Zealand, zero
> ads between programs on some channels, there is title scrolling and all
> that)
> 5) End of "P1" recording
> --> Live goes on
>
> I have found it *very* hard to get the over-recording right (I think they
> call it "island time" :D ). The best way for me is to set the pre-start
> recording time to 120 seconds and over record by 300 seconds. The problem
> this causes is that "all" my tuners are busy (hauppauge Nova S Plus)
>
> I am told this card can do up to 8 recordings (via that magic that Myth
> does) but I could have sworn the last time I set it to 8 the quality went
> down (the picture appeared snowy) If the card is happy to handle 8 decodes,
> then that solves my problem, but what about people that arn't that lucky.
>
> Here is what I thought could happen:
>
> At 3) - create another ring buffer that "feeds off" the already created ring
> buffer for 1)
> At 4) - release the ring buffer for 1)
> At 5) - release the ring buffer created at 3)
>
> I hope that makes sense, comments/flaming welcome
>

That method has been suggested but not implemented. I am sure you will
get the "patches welcome" response :)

Your DVB card does not decode. It pushes data to the hard drive. The
constraints are IO (including PIC/PCIe speeds and Disk IO).
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