satellite highlight delay?

Discussion in 'Satellite TV, Sky TV & FreeSat' started by merlin777, Dec 17, 2016.

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  1. merlin777

    merlin777
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    A friend has just shown me a clip of a programme on sky where a man is talking and moving his head slightly from side to side. One side of his face and nose is quite bright as it's lit by a window and these areas seem to lag slightly behind the rest of the picture. I'd estimate a frame or so. It gives the effect of his nose 'wobbling' like jelly!

    He recorded the clip by using his smart phone and pointing at the tv but the effect could be seen with the naked eye on his tv.

    Has anyone come across this type of thing before?

    It was BBC 1 on sky in standard def.
     
    Last edited by a moderator: Dec 18, 2016
  2. kevkbuk

    kevkbuk
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    Sounds like picture processing on the TV rather than the broadcast.
     
  3. noiseboy72

    noiseboy72
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    Usually a very low bandwidth satellite uplink. The way that MPEG compression works is that you only send bits of the picture that have changed and reuse the rest. When bandwidth drops really low, the picture cannot be correctly reassembled from the available information and this sort of image distortion occurs.
     
  4. merlin777

    merlin777
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    These were my first thoughts too.

    However, it seems to be just the area of highlight, not his whole head which is all moving. Also, it's a smooth artefact and not blocky. I'm having trouble matching that with other mpeg decoding artefacts that I know of.
     
  5. noiseboy72

    noiseboy72
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    Without seeing the clip, it's impossible to say, but encoding can give smooth, non blocky errors, but possibly it could be a processing thing on the TV. I doubt it would be the camera, as broadcast equipment is very stable with high quality wide dynamic range sensors that don't require much in the way of processing in terms of acquiring scenes with different brightness levels.
     
  6. merlin777

    merlin777
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    I work in broadcasting and I too doubt it's any part of the pre-broadcast chain. An uncompressed digital signal is almost bullet proof. I'll see if I can upload the clip.

    Here's a dropbox link. I've left some of the previous shot too.

    Dropbox - sample.mp4
     
  7. kevkbuk

    kevkbuk
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    Surely the TV... never seen anything like that on a plasma with all image 'enhancements' off.
     
  8. merlin777

    merlin777
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    I agree it's the TV - but what is causing it?
     
  9. noiseboy72

    noiseboy72
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    Looks like some sort of anti-flicker processing got confused. As that's a finished production, it's going to be legal colours and levels and I cannot see how that sort of error would happen as part of the broadcast, so my money is on some processing on the TV.
     
  10. merlin777

    merlin777
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    it's turned out to be a function on the tv called truemotion - apparently it interpolates extra frames rather than displacing them twice.
     

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