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Bad picture on Pioneer DVR-420H recordings

Discussion in 'Blu-ray & DVD Players & Recorders' started by brownrog, Dec 6, 2004.

  1. brownrog

    brownrog
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    Unsure if this should be on TV forum, but I put it here because it's a quite technical one! :confused:

    I am getting nasty blocky pictures on playback of HDD recordings from UKTV History on Freeview. The progamme was Alan Eneira's "The Kings & Queens of England" (please, no royals jokes! :) )

    The problem occurs only on footage of historical reconstructions. Studio shots of Eneira, modern film footage (eg of modern royals), interview shots etc are all fine. But the reconstruction footage (using actors as historical characters) are almost unwatchable with bad pixellation.

    The progs were recorded in SP mode (2 hours on 4.7GB DVD) on the HDD. Unfortunately I was not able to watch the actual broadcast quality. The tuner is a Thomson DTI1000 feeding RGB to the 420H. Signal level is good. The problem has not occurred on any other recordings of terrestrial TV; I have not recorded anything else from UKTV History, however.

    Anyone else encountered this and can anyone suggest what might be going on please?
     
  2. johnjackthom

    johnjackthom
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    Was there a large amount of detail in the reconstruction footage or were there a number of dissolves taxing the UKTV mpeg encoder?

    My guess is that UKTV History has a pretty low bitrate and is easily caught out by "difficult" scenes.

    From what you describe I certainly wouldn't blame the DVD recorder for this problem.
     
  3. tabatha

    tabatha
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    I agree with johnjackthom - it is far more likely to be the bitrate of the transmission than the Pioneer. Most "flagship" channels are given a much higher share of the available bandwidth than some of the channels Sky consider less worthy. I always think this just goes to show how people should not believe the marketing blurb about the "superior quality digital television". It can be excellent but all too often the greedy broadcasters try to squeeze as many channels into the available bandwidth as they can get away with. Years ago the ITA/IBA had technical standards that commercial broadcasters (TV and Radio) had to adhere to or they could be fined. By the early nineties, this was largely scrapped and broadcasters were allowed to do just about what they wanted so far as technical quality is concerned. This has led to a general reduction in overall quality both of TV and Radio quality. Digital Radio is no better as the British have the worst quality DAB radio in the world - "never mind the quality - see how many channels there are". DAB is still promoted as being better quality than analogue when this is seldom true. The best DAB quality in the world is in Estonia! For more info on this see http://www.digitalradiotech.co.uk/worldwide_dab.htm
     
  4. brownrog

    brownrog
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    Thanks for these replies. Yes I suspect UKTV's compression and bit-rate combination. The reconstruction scenes were a mixture of quite fast-motion shots and more static shots. The pixel structure was evident on both. Slightly out-of-focus parts of the frame (trees in b/g) were totally pixellated green rectangles, almost unrecognisable. Even I (cynic that I am) found it hard to believe a broadcaster would allow that to happen on a transmission. The thing that still interest me is that all the other footage in these same progs is fine. I'm still unsure what properties of the frames in the "reconstruction" scenes would cause this in a codec and how the result occurs. I'd be less surprised if the delineation between good and bad quality in the programme was time-based (eg a time-based bandwidth reduction) but it's definitely the type of scene.

    If our suspicion is basically right, though, it shows how gullible some folk are who post on these forums that digital TV picture quality is better "because it's digital" (just read one of those)!
     
  5. gpward

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    Some producers of history TV programmes like to use an "archive" look for some scenes. This involves deliberately adding large amounts of noise (random moving speckle) to the picture, to make it look like an old film. MPEG-2 does not cope well with noise, so this gives both the broadcast MPEG-2 encoder and the one in your home DVD recorder a hard time. When an MPEG-2 encoder gets stressed, the picture goes blocky. If you record an already-blocky picture on your home DVD recorder, it will look even worse!

    You may notice similar problems with other "creative" TV effects such as image layering and long crossfades.
     
  6. brownrog

    brownrog
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    Thanks gpward, I think this is a very good summary of what is probably happening. I do suspect an interaction between some form of post-production effect (filter) applied to the historical reconstruction footage, the MPEG-2 codecs and (perhaps) the limited transmission bandwidth.

    I also think you're probably right about the impact of double encoding (transmission and recording) since I don't really want to believe that even UKTV, broadcasting on a minority interest channel, would accept a reception standard that turns trees into swathes of meaningless green blobs and actors' faces and hands into badly animated klingons.

    I've only had the recorder a couple of weeks - fortunately this is the only example in 50+ hours of recorded DTTV material, including other stuff from UKTV History. The rest is pretty much up to original broadcast SDTV standards when recorded in SP mode (2 hours per 4.7GB DVD-R) and viewed from playback on a 70 inch front projection screen.
     
  7. gpward

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    The MPEG-2 broadcast picture quality on the documentary channels in the UK is poor, due to limited budgets. Also, your large TV will show up bad picture quality far more effectively than a smaller one, just because problems are more noticeable when they are big!
     
  8. brownrog

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    Yes, of course - quite often I shrink the picture size down with the projector zoom on some sources and materials to make things nicer to watch (mind you it's still quite a big picture).

    But this is SO bad it would look terrible on a 17 inch screen! :rolleyes:
     

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