How good is Sky+ SDI?

Discussion in 'General TV Discussions Forum' started by Welwynnick, Nov 4, 2005.

  1. Welwynnick

    Welwynnick
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    The discussion of Sky HD prices has made me think. I’ve always been convinced that digital TV is used to squeeze more channels into a fixed bandwidth, rather than to improve picture quality. However, watching some of the Sky Movie channels recently on an ordinary CRT TV, it does seem like PQ is reasonable if there isn’t too much motion. Then, I thought it was comparable with DVD, in fact.

    However, if I watch DVDs on a good PC, the PQ is very much better than on TV, and better than almost all of the HD demonstrations that the High Street shops have been doing recently. In fact, I imagine the PC gives a similar picture to that yardstick of DVD reproduction, an SDI modded DVD player feeding a suitable scaler and HD display. That really extracts very much more from a DVD than does an ordinary player and TV.

    Now, many people have said that an SDI modded Mk1 Sky+ box with such a scaler also provides a great improvement to PQ. If the improvement is as great as it is with DVD, then I would have to wonder if a Sky HD box really makes that much sense.

    Can anyone tell me the SDI benefit with Sky is as great as it is with DVD?

    Regards, Nick

    Mods - could you correct the thread title to "How good is Sky + SDI?" Cheers.
     
  2. Kramer

    Kramer
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    Yep, done.

    :smoke:
     
  3. TheDoctor

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    Hi Nick

    I think it is easier to quantify the benefit with SDI DVD, compared to SDI SKY. The thing is..... today 95% of DVDs are produced to a reasonable standard. With a scaler you are more than likely to get a great picture all the time.

    When it comes to TV, the broadcast standards are all over the place. With some channels, you will get DVD-like quality (e.g premiership, new SKY movie releases, new documentaries.) The poor channels will remain poor, although they will be more watchable.

    The difference the SDI/scaler makes is a significant improvement and good broadcasts look great.

    When SKY HD comes out, I will stick to my SDI solution for a while longer. My main reason for this is, that I would like to archive HD material and watch it again, but this will not be possible with the new SKY HD boxes.

    I will not be paying extra to watch something "once" and say wow!!!! If that's the case, I would rather go to the cinema.

    Doc
     
  4. TheDoctor

    TheDoctor
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    I may change my mind, if you could SDI-mod the SKY HD box. That way you could stream the digital video directly to a PC, for capturing.

    The other option would be to incorparate Firewire outputs in the boxes for capturing HD, like in the USA.
     
  5. Docta teef

    Docta teef
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    When SKY HD comes out, I will stick to my SDI solution for a while longer. My main reason for this is, that I would like to archive HD material and watch it again, but this will not be possible with the new SKY HD boxes.

    I will not be paying extra to watch something "once" and say wow!!!! If that's the case, I would rather go to the cinema.

    Doc[/QUOTE]

    This is exactly what im thinking im not gonna pay extra for a small amount of stuff you cannot copy. When the BBC ect start to use it it may be a different matter but my plan for now is a scaler and an sdi mod
     
  6. Stephen Neal

    Stephen Neal
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    You'd have to add an HD-SDI not an SDI output - as SDI runs at 270Mbs which is not fast enough for HD. HD-SDI maxes out at around the 1.2Gbps mark which is required to carry uncompressed 4:2:2 1080/50i.

    HD-SDI and SDI are based around the 1125 and 750 total line scanning system not the 1080 / 720 active line system as they are designed to allow conversion to and from analogue signals without frame buffering, hence they run at a higher data rate than would be required just to carry the active video. (You can't just do a 1920x1080x25x 16 or 20 - depending on 8 or 10 bit 4:2:2 being used - calculation to work out the data rate - you have to allow for horizontal and vertical blanking)

    Similarly you'd need an HD-SDI input card for your PC. These are available - but you'd need a decent speed hard drive - and probably a RAID array to record at a sustained 1.2Gbps (150MB/s) reliably.

    Yep - though all the firewire solutions in the US are based on MPEG2 - and the Sky HD system will be MPEG4.

    Sky won't be providing a Firewire output - and I'm not sure there is yet a standard for carrying an MPEG4 video signal in an MPEG transport stream that will work with existing firewire devices - though I'm sure a PC solution could be hacked, if the right bits of data can be found on the Sky PCB.

    I suspect Sky will be trying to avoid the un-encrypted digital video being available anywhere on their PCB - especially as this would allow circumvention of HDMI...
     
  7. TheDoctor

    TheDoctor
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    Hi Stephen

    Sorry I did mean HD-SDI, there have been a few discussions on the PMS forums, regarding this technology (following the introduction of Crystalio II). I am confident that a PC solution will be available.

    But it is all hopes and speculation at the moment with this new SKY HD box. The "experts" need to get their hands on one first.

    Doc
     
  8. Neil F Holland

    Neil F Holland
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    Suspect you mean circumvention of HDCP... ;)

    Interesting thread - and very good technical stuff.
     
  9. Stephen Neal

    Stephen Neal
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    Yes - I did mean HDCP!
     
  10. Stephen Neal

    Stephen Neal
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    PCI HD-SDI capture solutions are already available for non linear editing of HD material - as many NLEs are now based on Wintel PCs. However the disk bandwith to record a 1.2Gbps stream is still significant, as is the size of storage! Real-time compression will rely on hardware for the time being - though with the advent of HDV camcorders, consumer price point HD MPEG2 encoders must have been developed.
     

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