Mailing List Archive: MythTV: Users

Flickering lines at the bottom of TV

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brian.phillips at gmx

Jul 21, 2008, 5:24 PM

Post #1 of 11 (1017 views)
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Flickering lines at the bottom of TV

Hello,

I have a problem where my recordings on one of my channels of analog cable
have a flickering line at the bottom (and sometimes top) of the screen.
It's mainly the bottom. I've got a screenshot here:

http://www.et.byu.edu/~bphilli7/pics/law.png

I don't know how to describe what it is, but I was hoping someone on the
list could tell me what causes it and what I can do to fix it.

It only happens on one of my 20 or so cable channels I get. I was thinking
it might be a tuning issue (maybe fine tuning the frequency for that channel
could fix it) or something in that same vein. Anyone know what causes that
flickering line? It's not always there. It's just always there on that
channel.

Brian Phillips

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myth at dermanouelian

Jul 21, 2008, 5:32 PM

Post #2 of 11 (968 views)
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Re: Flickering lines at the bottom of TV [In reply to]

On Jul 21, 2008, at 5:24 PM, Brian Phillips wrote:

> Hello,
>
> I have a problem where my recordings on one of my channels of analog
> cable
> have a flickering line at the bottom (and sometimes top) of the
> screen.
> It's mainly the bottom. I've got a screenshot here:
>
> http://www.et.byu.edu/~bphilli7/pics/law.png
>
> I don't know how to describe what it is, but I was hoping someone on
> the
> list could tell me what causes it and what I can do to fix it.
>
> It only happens on one of my 20 or so cable channels I get. I was
> thinking
> it might be a tuning issue (maybe fine tuning the frequency for that
> channel
> could fix it) or something in that same vein. Anyone know what
> causes that
> flickering line? It's not always there. It's just always there on
> that
> channel.

It's being broadcast that way. There is nothing to fix on your end.
Usually a television's overscan will hide this sort of thing but since
you're displaying the entire video, you're getting the garbage* edges
as well.
For info on Overscan here: http://www.mythtv.org/wiki/index.php/Overscan

To hide this, you can play back your videos 1% or 2% larger than they
actually are (whichever works for you) or you can crop your recordings
by transcoding them with crop settings.
http://www.mythtv.org/wiki/index.php/Overscan#TV_Playback_Overscan_Adjustment_Settings

*The "garbage" is actually encoded information being sent along with
the broadcast like metadata information about the program, closed
captioning text, etc.
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allen.edwards at oldpaloalto

Jul 21, 2008, 6:26 PM

Post #3 of 11 (971 views)
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Re: Flickering lines at the bottom of TV [In reply to]

Brad DerManouelian wrote:
> On Jul 21, 2008, at 5:24 PM, Brian Phillips wrote:
>
>> Hello,
>>
>> I have a problem where my recordings on one of my channels of analog
>> cable
>> have a flickering line at the bottom (and sometimes top) of the
>> screen.
>> It's mainly the bottom. I've got a screenshot here:
>>
>> http://www.et.byu.edu/~bphilli7/pics/law.png
>>
>> I don't know how to describe what it is, but I was hoping someone on
>> the
>> list could tell me what causes it and what I can do to fix it.
>>
>> It only happens on one of my 20 or so cable channels I get. I was
>> thinking
>> it might be a tuning issue (maybe fine tuning the frequency for that
>> channel
>> could fix it) or something in that same vein. Anyone know what
>> causes that
>> flickering line? It's not always there. It's just always there on
>> that
>> channel.
>
> It's being broadcast that way. There is nothing to fix on your end.
> Usually a television's overscan will hide this sort of thing but since
> you're displaying the entire video, you're getting the garbage* edges
> as well.
> For info on Overscan here: http://www.mythtv.org/wiki/index.php/Overscan
>
> To hide this, you can play back your videos 1% or 2% larger than they
> actually are (whichever works for you) or you can crop your recordings
> by transcoding them with crop settings.
> http://www.mythtv.org/wiki/index.php/Overscan#TV_Playback_Overscan_Adjustment_Settings
>
> *The "garbage" is actually encoded information being sent along with
> the broadcast like metadata information about the program, closed
> captioning text, etc.
> _______________________________________________
> mythtv-users mailing list
> mythtv-users [at] mythtv
> http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
>
One of the really nice things about mythtv is the ability to set the
size on playback to +3% to get rid of these lines. I have had dedicated
decoder boxes that could not do this. Anyway, it is in one of the setup
menus in myth under TV playback.

Allen

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brian.phillips at gmx

Jul 21, 2008, 6:34 PM

Post #4 of 11 (963 views)
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Re: Flickering lines at the bottom of TV [In reply to]

Brad DerManouelian wrote:
> It's being broadcast that way. There is nothing to fix on your end.
> Usually a television's overscan will hide this sort of thing but
> since you're displaying the entire video, you're getting the garbage*
> edges as well.
> For info on Overscan here:
> http://www.mythtv.org/wiki/index.php/Overscan
>
> To hide this, you can play back your videos 1% or 2% larger than they
> actually are (whichever works for you) or you can crop your
> recordings by transcoding them with crop settings.
>
http://www.mythtv.org/wiki/index.php/Overscan#TV_Playback_Overscan_Adjustmen
t_Settings
>
> *The "garbage" is actually encoded information being sent along with
> the broadcast like metadata information about the program, closed
> captioning text, etc.

I was a bit skeptical of overscan being my issue for a couple reasons. 1)
It only happens on a single channel. 2) It doesn't happen 100% of the time
(but often enough it's worth delving into.).

I'll look into the scan displacement settings.

Brian Phillips

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myth at dermanouelian

Jul 21, 2008, 6:55 PM

Post #5 of 11 (964 views)
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Re: Flickering lines at the bottom of TV [In reply to]

On Jul 21, 2008, at 6:26 PM, Allen Edwards wrote:

> Brad DerManouelian wrote:
>> To hide this, you can play back your videos 1% or 2% larger than they
>> actually are (whichever works for you) or you can crop your
>> recordings
>> by transcoding them with crop settings.
>> http://www.mythtv.org/wiki/index.php/Overscan#TV_Playback_Overscan_Adjustment_Settings
>>
> One of the really nice things about mythtv is the ability to set the
> size on playback to +3% to get rid of these lines. I have had
> dedicated
> decoder boxes that could not do this. Anyway, it is in one of the
> setup
> menus in myth under TV playback.

One of the really nice things about my response is that I explained
this and even included a link on where/how to do it. ;)

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myth at dermanouelian

Jul 21, 2008, 6:55 PM

Post #6 of 11 (967 views)
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Re: Flickering lines at the bottom of TV [In reply to]

On Jul 21, 2008, at 6:34 PM, Brian Phillips wrote:

> I was a bit skeptical of overscan being my issue for a couple
> reasons. 1)
> It only happens on a single channel. 2) It doesn't happen 100% of
> the time
> (but often enough it's worth delving into.).

I can do better than that. It only happens for me on certain shows on
a particular channel. ;)

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allen.edwards at oldpaloalto

Jul 21, 2008, 7:15 PM

Post #7 of 11 (957 views)
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Re: Flickering lines at the bottom of TV [In reply to]

Brian Phillips wrote:
> Brad DerManouelian wrote:
>> It's being broadcast that way. There is nothing to fix on your end.
>> Usually a television's overscan will hide this sort of thing but
>> since you're displaying the entire video, you're getting the garbage*
>> edges as well.
>> For info on Overscan here:
>> http://www.mythtv.org/wiki/index.php/Overscan
>>
>> To hide this, you can play back your videos 1% or 2% larger than they
>> actually are (whichever works for you) or you can crop your
>> recordings by transcoding them with crop settings.
>>
> http://www.mythtv.org/wiki/index.php/Overscan#TV_Playback_Overscan_Adjustmen
> t_Settings
>> *The "garbage" is actually encoded information being sent along with
>> the broadcast like metadata information about the program, closed
>> captioning text, etc.
>
> I was a bit skeptical of overscan being my issue for a couple reasons. 1)
> It only happens on a single channel. 2) It doesn't happen 100% of the time
> (but often enough it's worth delving into.).
>
> I'll look into the scan displacement settings.
>
> Brian Phillips
>
This is standard stuff. I have been watching HDTV for about 6 years and
this stuff drove me nuts for a long time. The "garbage" is a data
signal and it is not there on all broadcasts. I think it is in the
analog programs and it comes along for the ride on the DTV transmission
if not removed by the broadcaster. Perhaps it is CC data, I don't know.

Anyway, it is perfectly normal to see it and perfectly normal to add 3%
or so of overscan. You never noticed it on your analog sets because
they all have overscan to get rid of this stuff.

Allen
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brian.phillips at gmx

Jul 21, 2008, 7:22 PM

Post #8 of 11 (969 views)
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Re: Flickering lines at the bottom of TV [In reply to]

Brad DerManouelian wrote:
> On Jul 21, 2008, at 6:34 PM, Brian Phillips wrote:
>
>> I was a bit skeptical of overscan being my issue for a couple
>> reasons. 1) It only happens on a single channel. 2) It doesn't
>> happen 100% of the time (but often enough it's worth delving into.).
>
> I can do better than that. It only happens for me on certain shows on
> a particular channel. ;)

So is the only option to displace the scan on ALL programs if you ever want
to watch that show/channel on livetv? And if you can wait until a userjob
ends to crop the bottom lines off?

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brian.phillips at gmx

Jul 21, 2008, 7:24 PM

Post #9 of 11 (964 views)
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Re: Flickering lines at the bottom of TV [In reply to]

Allen Edwards wrote:
> This is standard stuff. I have been watching HDTV for about 6 years
> and this stuff drove me nuts for a long time. The "garbage" is a
> data signal and it is not there on all broadcasts. I think it is in
> the analog programs and it comes along for the ride on the DTV
> transmission if not removed by the broadcaster. Perhaps it is CC
> data, I don't know.
>
> Anyway, it is perfectly normal to see it and perfectly normal to add
> 3% or so of overscan. You never noticed it on your analog sets
> because they all have overscan to get rid of this stuff.
>
> Allen

There's not an ounce of digital on these cable lines. It's a college campus
where the have IP television feeds. I'm in one of the housing units and
they have a DAC setup where they do the IPTV to analog conversion and then
modulate it to the us-cable frequency table. They're too cheap for anything
digital.

Brian

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myth at dermanouelian

Jul 21, 2008, 7:25 PM

Post #10 of 11 (960 views)
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Re: Flickering lines at the bottom of TV [In reply to]

On Jul 21, 2008, at 7:22 PM, Brian Phillips wrote:

> Brad DerManouelian wrote:
>> On Jul 21, 2008, at 6:34 PM, Brian Phillips wrote:
>>
>>> I was a bit skeptical of overscan being my issue for a couple
>>> reasons. 1) It only happens on a single channel. 2) It doesn't
>>> happen 100% of the time (but often enough it's worth delving into.).
>>
>> I can do better than that. It only happens for me on certain shows on
>> a particular channel. ;)
>
> So is the only option to displace the scan on ALL programs if you
> ever want
> to watch that show/channel on livetv? And if you can wait until a
> userjob
> ends to crop the bottom lines off?

Well, I chose the option of ignoring the lines but yeah, your options
to get rid of the lines are to increase the size of all your programs
or transcode them when they're done recording with a user job. I
promise that you won't notice the missing 2% or so once you set it. In
fact, that's the way the programs are meant to be presented.
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allen.edwards at oldpaloalto

Jul 21, 2008, 9:12 PM

Post #11 of 11 (962 views)
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Re: Flickering lines at the bottom of TV [In reply to]

>
> There's not an ounce of digital on these cable lines. It's a college campus
> where the have IP television feeds. I'm in one of the housing units and
> they have a DAC setup where they do the IPTV to analog conversion and then
> modulate it to the us-cable frequency table. They're too cheap for anything
> digital.
>
> Brian
>
Whatever, you are apparently watching the show on something that doesn't
have overscan and the "data" (Closed Caption perhaps)is showing. The
fact that it is not DTV explains why you are seeing it on the bottom as
well as the top. I wondered about that as if it was digital, it would
only be on top.

As another poster said, analog TV is intended to have overscan. There
is a good discussion here http://en.wikipedia.org/wiki/Overscan

Just set it to 3%, you will be fine. You won't miss anything as this is
how it is intended to be viewed. I see in the wiki that BBC recommends
3.5%, for example.

Allen

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