Mailing List Archive

1 tuner, overlap consecutive recordings on single channel
This has been kicking around in my head for a while, and I've finally put my
finger on exactly what's occurring. I only have 1 tuner (PVR-250), and I'm
running the latest 0.18-fixes (rev 8079).

My default settings (global start recording 12 seconds before, end recording
20 seconds late) work for most single recordings, but there's always the
exception here and there. And the global modifiers are (I think) thrown out
the window on a transition from show to show when recording consecutive shows.
This is currently cropping up on Scifi channel, where I'm recording several
episodes of Stargate SG1 that I haven't seen previously. Since they often run
in mini-marathons, I wind up with the first episode truncated, and perhaps
5-10 seconds of the first episode in the second recording.

This isn't the end of the world, but there is often a few seconds of missing
data when this happens.

However, I remember seeing some episodes of a different show (Good Eats) that
consistently had the same (20 second) segment exist in both the end of the
first recording, and the beginning of the second. This seemed heartening.

Looking at my recording settings, the only difference is that Stargate SG1 is
set to start/end "on time", while Good Eats is set to record 1 minute past the
end. So I theorized that this behavior only affected consecutive recordings
on the same channel that also had a hard setting for extending the end time.

When testing this theory, I find that selecting the "add 1 minute to
recording" option will now cause conflicts, even when the same show is being
aired consecutively on the same channel.

Has this behavior changed? Because what I was seeing seemed to be the ideal
behavior, IMO. When recording consecutive shows with the same tuner, same
channel, same recording profile, allow the extra time specified in the global
setting to exist in both recordings. I don't see anything relevant in the
change logs or the user/dev lists, although there have been discussions on how
to handle this situation.

Thanks,
Mark
Re: 1 tuner, overlap consecutive recordings on single channel [ In reply to ]
Mark Staudinger wrote:

>This has been kicking around in my head for a while, and I've finally put my
>finger on exactly what's occurring. I only have 1 tuner (PVR-250), and I'm
>running the latest 0.18-fixes (rev 8079).
>
>My default settings (global start recording 12 seconds before, end recording
>20 seconds late) work for most single recordings, but there's always the
>exception here and there. And the global modifiers are (I think) thrown out
>the window on a transition from show to show when recording consecutive shows.
> This is currently cropping up on Scifi channel, where I'm recording several
>episodes of Stargate SG1 that I haven't seen previously. Since they often run
>in mini-marathons, I wind up with the first episode truncated, and perhaps
>5-10 seconds of the first episode in the second recording.
>
>This isn't the end of the world, but there is often a few seconds of missing
>data when this happens.
>
>However, I remember seeing some episodes of a different show (Good Eats) that
>consistently had the same (20 second) segment exist in both the end of the
>first recording, and the beginning of the second. This seemed heartening.
>
>Looking at my recording settings, the only difference is that Stargate SG1 is
>set to start/end "on time", while Good Eats is set to record 1 minute past the
>end. So I theorized that this behavior only affected consecutive recordings
>on the same channel that also had a hard setting for extending the end time.
>
>When testing this theory, I find that selecting the "add 1 minute to
>recording" option will now cause conflicts, even when the same show is being
>aired consecutively on the same channel.
>
>Has this behavior changed? Because what I was seeing seemed to be the ideal
>behavior, IMO. When recording consecutive shows with the same tuner, same
>channel, same recording profile, allow the extra time specified in the global
>setting to exist in both recordings. I don't see anything relevant in the
>change logs or the user/dev lists, although there have been discussions on how
>to handle this situation.
>
>
per show pre/post roll settings are hard and will bump other recordings
no matter what. There really isn't much you can do to prevent the
overlap you are seeing because the network isn't broadcasting in the
correct timeslots and with only one tuner, you can't use the per program
pre/post roll as explained...

Kevin

--
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RE: 1 tuner, overlap consecutive recordings on single channel [ In reply to ]
> My default settings (global start recording 12 seconds
> before, end recording 20 seconds late) work for most single
> recordings, but there's always the exception here and there.
> And the global modifiers are (I think) thrown out the window
> on a transition from show to show when recording consecutive shows.
> This is currently cropping up on Scifi channel, where I'm
> recording several episodes of Stargate SG1 that I haven't
> seen previously. Since they often run in mini-marathons, I
> wind up with the first episode truncated, and perhaps 5-10
> seconds of the first episode in the second recording.

There is no substitute for 2 tuners. Once you have 2 you will never go back.
:)
Re: 1 tuner, overlap consecutive recordings on single channel [ In reply to ]
On 11/29/05 16:14, Mark Staudinger wrote:

>However, I remember seeing some episodes of a different show (Good Eats) that
>consistently had the same (20 second) segment exist in both the end of the
>first recording, and the beginning of the second. This seemed heartening.
>
>Looking at my recording settings, the only difference is that Stargate SG1 is
>set to start/end "on time", while Good Eats is set to record 1 minute past the
>end. So I theorized that this behavior only affected consecutive recordings
>on the same channel that also had a hard setting for extending the end time.
>
>When testing this theory, I find that selecting the "add 1 minute to
>recording" option will now cause conflicts, even when the same show is being
>aired consecutively on the same channel.
>
>Has this behavior changed?
>
Nope. It's never worked the way you're theorizing. There's something
more going on that you didn't notice. Are you sure the Good Eats
episodes were back to back?

Mike
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1 tuner, overlap consecutive recordings on single channel [ In reply to ]
Date: Tue, 29 Nov 2005 18:01:40 -0500
From: "Michael T. Dean" <mtdean@thirdcontact.com>

Nope. It's never worked the way you're theorizing. There's something
more going on that you didn't notice. Are you sure the Good Eats
episodes were back to back?

It would, however, be seriously cool if Myth could cope with this,
and I have an algorithm below for how.

[.One of my major annoyances with a single-tuner TiVo was trying to
simultaneously deal with imprecise start/stop station timings versus
back-to-back episodes; in general, if you don't want to lose the start
or end of something (and hence add pre/post-roll), a TiVo will miss
every other episode in a marathon, and so will a Myth. And if you
eliminate the pre/post-rolls, you're still not guaranteed not to have
the first or last few seconds of an episode wind up in the wrong
actual file, -and- you'll lose a few seconds no matter what as it
(unnecessarily!) reinitializes the tuner. The workaround there
required noticing the pattern before recording, and then manually
recording a giant block that spanned the entire time interval (and
had pre/post rolls at the ends). This means you lose the per-episode
information -and- can't delete a single one, since it's one giant
block.]

But Myth -could- do better that this---though it might require taking
too large a pair of pliers to its inner architecture (I don't know
enough to be sure). My proposed solution would be:
(a) Notice whenever a pair of recordings has a nonnegative temporal
overlap (e.g., they butt up against each other, or they actually
overlap each other---this overlap could be because of pre/post
rolls, or because of manual programming of start/stop times).
Whenever this happens, ensure that both recordings are forced to
the same tuner, and -do not reinitialize it- at any time during
the overlap. You want this to be true even during a butt and not
just an overlap, because you can lose many seconds while the tuner
gets told to retune even the same channel (tuner lock, OSDs from
some cable boxes, etc). [.Does Myth already have this do-not-retune
optimization? I'm wondering what happens if you have 2+ tuners fed
from one cable box that requires an IR blaster; many boxes will
display the channel number and/or pop up an OSD as it's "typed"
and that would ruin any recording still in progress, even if the
two tuners would otherwise handle the situation by each encoding
during the overlap interval. I don't have that sort of HW setup
(yet) so I can't test it.]
(b) During the overlap interval, copy data from the tuner to two
different files instead of just one (e.g., the files for the first
and second recordings). Yes, this doubles I/O to the disk for a
few minutes, but disk I/O bandwidth is plentiful. (And obviously,
if we're doing software encoding, that happens upstream of this so
it's only done once; all I'm talking about here is putting the
bits in two places, possibly with any required header when the
second file gets opened, and/or starting on the correct frame/
format boundary, etc---but all this code must already exist.)
(c) Iterate: consider each pair of recordings on the same channel
until you come to a gap. (This might just happen automatically
without any explicit iteration, depending on how (a) is done.)
This will consolidate any number of same-channel recordings.

This -seems- easy enough, but the devil is in the details: getting the
overlap detection integrated probably has some picky corner cases, and
I don't know if the internal architecture is flexible enough to dump a
stream to two files simultaneously. But they seem doable.

And this would make a reasonably common situation require -half- as
many tuners as it otherwise would, while leading to superior results.
(This really comes out if you're unlucky enough to want to record
-two- channels, each with back-to-back stuff; now you'd suddenly need
-four- tuners without this optimization.)

So it might be that a few dozen lines of code could save a bunch of
hardware.