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Regular flickering on NASA TV signal



 
 
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  #1  
Old August 26th 09, 01:57 AM posted to rec.video.satellite.dbs,alt.dbs.directv
Patty Winter
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Posts: 14
Default Regular flickering on NASA TV signal

A friend who also has DirecTV and I were watching the attempted
shuttle launch last night, and I asked him about a problem I've
seen occasionally on NASA TV. It's a slight "jumping" or pixelization
of the video about once per second. He said that he has seen the
same problem for the last two or three shuttle launches.

I just checked NASA TV on two other sources (over the air and
cable), and I don't see the problem there. So at first glance,
it would appear to be a purely DirecTV problem. But...I don't
see it all the time on NASA TV. It's as though at certain times,
the signal from NASA encounters something in the video chain
at DirecTV and the mixture creates the problem.

The jittering is very evident now that dusk has fallen in Florida.
I'm curious to see whether it will occur during the upcoming press
conference. Meanwhile, could those of you with DirecTV kindly go
over to channel 283 and let me know whether you're seeing that
slight pixelization about once per second on this long shot of
Discovery? (Please watch for a minute or two; it goes away briefly
sometimes.)


Thanks!
Patty

  #2  
Old August 26th 09, 10:56 PM posted to rec.video.satellite.dbs,alt.dbs.directv
LIRR Trainman
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Posts: 1
Default Regular flickering on NASA TV signal

Patty -

I think it's a symptom of digital compression. I'm also a subscriber to
MLB.tv (baseball over the internet) which relies quite heavily on
compression and when there's a static shot of the field you'll see
exactly what you describe at quite regular intervals, like once every
1-2 seconds.

Some channels carry higher compression rates than others, e.g. sporting
channels generally have lower compression than news or variety stations
to help with digital artifacts on high-motion scenes, but unfortunately
such artifacting is a way of satellite (and probably cable) life.

When I watch local TV through my digital converter box (haven't upgraded
to HDTV yet) the picture is outstanding in every way. DTV must cram so
much data on the birds that some channels bear the brunt of the mpeg
compression.

Hope this helps.

Frank



Patty Winter wrote:
A friend who also has DirecTV and I were watching the attempted
shuttle launch last night, and I asked him about a problem I've
seen occasionally on NASA TV. It's a slight "jumping" or pixelization
of the video about once per second. He said that he has seen the
same problem for the last two or three shuttle launches.

I just checked NASA TV on two other sources (over the air and
cable), and I don't see the problem there. So at first glance,
it would appear to be a purely DirecTV problem. But...I don't
see it all the time on NASA TV. It's as though at certain times,
the signal from NASA encounters something in the video chain
at DirecTV and the mixture creates the problem.

The jittering is very evident now that dusk has fallen in Florida.
I'm curious to see whether it will occur during the upcoming press
conference. Meanwhile, could those of you with DirecTV kindly go
over to channel 283 and let me know whether you're seeing that
slight pixelization about once per second on this long shot of
Discovery? (Please watch for a minute or two; it goes away briefly
sometimes.)


Thanks!
Patty

  #3  
Old August 26th 09, 11:29 PM posted to rec.video.satellite.dbs,alt.dbs.directv
Chris Adams
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Posts: 164
Default Regular flickering on NASA TV signal

Once upon a time, LIRR Trainman said:
I think it's a symptom of digital compression. I'm also a subscriber to
MLB.tv (baseball over the internet) which relies quite heavily on
compression and when there's a static shot of the field you'll see
exactly what you describe at quite regular intervals, like once every
1-2 seconds.


That sounds like you are seeing the MPEG keyframe. The basic way MPEG
compression works is by transmitting a single full-resolution frame (the
keyframe), that is then followed by frames that only have the
differences from the previous frame. A lot of streaming video (Internet
and TV) uses one keyframe per second.

When the compression is cranked up high on the keyframe, you can see the
keyframe kind of "pop". Even if little has changed in the image, the
high compression can affect successive keyframes a little bit
differently, so the artifacting shifts around.

One of my local cable HD channels (Universal HD) gets this way
sometimes, almost to the point of being unwatchable.

I'm no MPEG expert, so I may be wrong on the details, but this is how it
has been explained to me (more or less).
--
Chris Adams
Systems and Network Administrator - HiWAAY Internet Services
I don't speak for anybody but myself - that's enough trouble.
  #4  
Old August 27th 09, 05:47 PM posted to rec.video.satellite.dbs,alt.dbs.directv
Patty Winter[_2_]
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Posts: 228
Default Regular flickering on NASA TV signal


Thanks for the suggestions, Frank and Chris.

Would it be likely that feeds from certain cameras are compressed
more than others, and that's why we don't always see this "popping"?
For example, the long shot of the pad is going to have very little
movement in it (until launch!), whereas the camera where the
astronauts get into the shuttle would have much more. I'm just
riffing on your compression ideas here and wondering whether some
sources would be more compressed (and therefore more subject to
problems) than others.


Patty

  #5  
Old August 28th 09, 05:46 AM posted to rec.video.satellite.dbs,alt.dbs.directv
Chris Adams
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Posts: 164
Default Regular flickering on NASA TV signal

Once upon a time, Patty Winter said:
Would it be likely that feeds from certain cameras are compressed
more than others, and that's why we don't always see this "popping"?


Well, then it would be seen everywhere (cable, DirecTV, Dish, etc.).
The providers don't have access directly to NASA cameras; they are just
getting NASA-TV off the satellite. I guess that some of NASA's cameras
could be lower-resolution than others, and compounding the artifacting
with compression could be an issue, but that seems kind of a stretch.

I think it may also be that some images are just more susceptible to
this problem than others. I was watching the Atlanta Braves baseball
game (in HD here finally!) tonight, and noticed the same kind of "pop"
on certain outfield shots, but not on the rest of the shots. I know all
the cameras are the same, and they all are fed through the same truck,
so there wouldn't be any technical reason for a difference in video
compression or quality I wouldn't think.

However, the background in most shots is the crowd (lots of variation),
while the background in the "high-home" outfield shot is the grass, with
its wide pattern and the close texture, so maybe that has something to
do with it.

I'm planning to watch the shuttle launch Friday night on HDNet (hydrogen
and weather willing!). They carry the launches and landings in HD (even
if I'd rather listen to the NASA audio feed than the HDNet guy talking
over everything); I'll see what it looks like there.
--
Chris Adams
Systems and Network Administrator - HiWAAY Internet Services
I don't speak for anybody but myself - that's enough trouble.
  #6  
Old August 28th 09, 09:52 PM posted to rec.video.satellite.dbs,alt.dbs.directv
Patty Winter[_2_]
external usenet poster
 
Posts: 228
Default Regular flickering on NASA TV signal


In article ,
Chris Adams wrote:
Once upon a time, Patty Winter said:
Would it be likely that feeds from certain cameras are compressed
more than others, and that's why we don't always see this "popping"?


Well, then it would be seen everywhere (cable, DirecTV, Dish, etc.).


Unless something in the video chain at DirecTV is particularly
sensitive to the compression. Perhaps exaggerating it?

I'm planning to watch the shuttle launch Friday night on HDNet (hydrogen
and weather willing!).


:-) I really thought they had that hydrogen leak fixed when
fueling went okay on Monday. :-(

They carry the launches and landings in HD (even
if I'd rather listen to the NASA audio feed than the HDNet guy talking
over everything); I'll see what it looks like there.


How about turning down the audio and listening to NASA TV?
The absence of chattering commentators is one of the big
reasons I like watching launches from the source.

Chris Adams
Systems and Network Administrator - HiWAAY Internet Services


Cool--I have friends who've had a "Due South" site on Hiwaay
for eons!


Patty

  #7  
Old August 29th 09, 12:37 AM posted to rec.video.satellite.dbs,alt.dbs.directv
Chris Adams
external usenet poster
 
Posts: 164
Default Regular flickering on NASA TV signal

Once upon a time, Patty Winter said:
:-) I really thought they had that hydrogen leak fixed when
fueling went okay on Monday. :-(


This was a _different_ hydrogen problem, not the same leak as before.
Hydrogen is pesky stuff!

How about turning down the audio and listening to NASA TV?


I'm watching through TiVo, and that's my only connection to the cable
(so I can't watch video from one channel and listend to audio from
another).

Cool--I have friends who've had a "Due South" site on Hiwaay
for eons!


Well, I haven't been here for eons, but I have been here a while.
Thanks (to them) for business! :-)
--
Chris Adams
Systems and Network Administrator - HiWAAY Internet Services
I don't speak for anybody but myself - that's enough trouble.
  #8  
Old August 29th 09, 01:12 AM posted to rec.video.satellite.dbs,alt.dbs.directv
Patty Winter[_2_]
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Posts: 228
Default Regular flickering on NASA TV signal


In article ,
Chris Adams wrote:
Once upon a time, Patty Winter said:

How about turning down the audio and listening to NASA TV?


I'm watching through TiVo, and that's my only connection to the cable
(so I can't watch video from one channel and listend to audio from
another).


Oh. Do you have Internet access where the TV is? You could listen
to NASA TV on your computer. :-)


Patty

  #9  
Old August 29th 09, 03:30 AM posted to rec.video.satellite.dbs,alt.dbs.directv
Chris Adams
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Posts: 164
Default Regular flickering on NASA TV signal

Once upon a time, Patty Winter said:
Oh. Do you have Internet access where the TV is? You could listen
to NASA TV on your computer. :-)


I have Internet access everywhere in my house; doesn't everybody have
gigabit switches (yes, plural) in their house? :-)

The Internet feed of NASA-TV lags something like 30-60 seconds, so that
doesn't work very well unfortunately. Actually, from times I've
switched back and forth, NASA-TV and HDNet are not in sync either, but
the difference is only a few seoncds IIRC.
--
Chris Adams
Systems and Network Administrator - HiWAAY Internet Services
I don't speak for anybody but myself - that's enough trouble.
  #10  
Old September 13th 09, 11:39 AM posted to rec.video.satellite.dbs,alt.dbs.directv
joeturn
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Posts: 33
Default Regular flickering on NASA TV signal

I saw NASA burnt another $mil testing the return to the moon thingy
last weak. Now I cant wait till they show how they expect to land that
sob on the moon and take off again.Their other lunar hoax did not
fool many I hope!

Then again stupidity is to the bone!

$$$$$$$$$$$$$$$$$$$$$$$
 




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