OTA HD vs Mpeg4 HD

Discussion in 'DirecTV TiVo Powered PVRs & Receivers' started by buzzmc1, Dec 22, 2005.

  1. Dec 28, 2005 #41 of 118
    Brewer4

    Brewer4 New Member

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    Thanks for being the only one that answered the question. It really was a simple one that asked if you could subjectively tell the difference if you had them side by side. I only need D* for ABC which is 90% OTA for me but is the weakest signal so I would like the D* sat feed for that one. The rest, I will continue to use OTA. Still a very interesting question.
     
  2. Dec 28, 2005 #42 of 118
    f300v10

    f300v10 New Member

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    No problem. I have not watched that much on the H20, since I have the HR10-250 and get pretty good OTA reception, unless the wind is blowing and then it sucks (dynamic multipath caused by lots of tall trees). That is the main reason I got the H20, for a backup when it is windy. I checked out Leno last night on the H20, and to my supprise, it looked real good on the D* local HD channel. I will try to watch more tonight, maybe D* has adjusted something to improve the Atlanta NBC.
     
  3. Dec 28, 2005 #43 of 118
    DeDondeEs

    DeDondeEs Well-Known Member

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    Actually anyone posting about MPEG-4 is on the wrong website since Tivo's don't record in MPEG-4 and this is the Tivo Community. Read the sticky at the top of this forum. The AVS forum has plenty of great posts on this topic.
     
  4. Dec 28, 2005 #44 of 118
    dswallow

    dswallow Save the ModeratŠ¾r TCF Club

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    Except it'd be fair game because the HR10-250 records what they're comparing it against.
     
  5. Dec 28, 2005 #45 of 118
    TyroneShoes

    TyroneShoes HD evangelist

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    OK, you have made a good point. And I apologize for saying exactly what everyone else was thinking. Anyone offended, let me know how I can make it up to you. Offending folks who have offended me was not my intent, it was more to stick up for the natural evolution of forum threads. In other words, it was me saying "cut me a break...can't you see we're trying to have a conversation here?". But I'm a work in progress, and I sometimes have little tolerance for those with little tolerance. No excuse for it...I'll simply count to ten from now on.
     
  6. Dec 28, 2005 #46 of 118
    TyroneShoes

    TyroneShoes HD evangelist

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    The MPEG decoder accepts an MPEG-encoded data stream from the hard drive and converts it into SDI video (HD SDI in this case), which is real-time uncompressed digital video. Missing information discarded in the encoding process is replicated according to a set of rules established by the encoding algorithm, essentially making educated guesses, and filling in the gaps created by encoding, hopefully cleverly enough so that we won't notice that it might actually be slightly different from the original encoded information.

    That said, I think there must be at least two decoders in any 2-channel PVR. I don't know of decoders that can decode multiple streams simultaneously, at least at the consumer level. For a box capable of both M4 and M2, one decoder also capable of both would be needed for each decoded video stream, or possibly two M2 and two M4 decoders.
     
  7. Dec 28, 2005 #47 of 118
    Phantom Gremlin

    Phantom Gremlin Active Member

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    Why do people think there need to be two MPEG decoders? Decoders are only used for viewing a video stream. So unless the PVR can simultaneously display multiple video streams it doesn't need multiple decoders. Or do you think that you are flipping between multiple streams too quickly for the PVR software to reprogram a single decoder quickly enough to keep up?

    BTW, apparently there is a cable HD box that can simultaneously "record to VCR" a different stream than it is displaying. That box would need two decoders.
     
  8. Dec 28, 2005 #48 of 118
    Budget_HT

    Budget_HT Heavy User (of TiVo)

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    I don't know what the new MPEG-4-capable HD DVR will bring, but I do know that each of my SD and HD DirecTV DVRs with TiVo only show one stream at a time, thus they must be limited to a single decoder if I understand this correctly.

    They can record two and playback a prerecorded third, but no matter what, they only output one at a time.
     
  9. Dec 28, 2005 #49 of 118
    bdlucas

    bdlucas Right side up again.

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    I think you are correct; there's no need for more than one MPEG-2 decoder in the HR10-250.
     
  10. Dec 29, 2005 #50 of 118
    bdlucas

    bdlucas Right side up again.

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    I don't know who's at fault for the backlevel and slow software on our HD TiVo's, nor do I think anyone posting to this forum really knows (or if they did their employer probably wouldn't be happy about their publicizing the information). I can tell you from first-hand experience that the realities of bringing a hardware/software product to market can cause all manner of anomalies that are baffling to an outsider and correspondingly frustrating to someone involved in the process. The explanation is usually complicated, with plenty of blame to go around.

    Here's a hypothetical scenario (drawn very loosely from personal experience) to illustrate what I mean. I am not suggesting that this is what happened, but rather only illustrating the kind of thing that can produce strange results in the 20/20 hindsight of us couch potatoes. So please don't debate the following as if it were a theory of what actually happened with TiVo and DirecTV!

    Suppose a product is planned for release on a particular date. The software is contracted out, commitments are made, resources are allocated to develop the software, and the software is ready on the planned release date as per contract. But suppose that meanwhile for whatever reason - market changes, strategic changes, management/ownership changes, poor planning, unforseen difficulties designing and producing the hardware - the product release date is pushed out. Suppose even worse it goes into a month-by-month slip, with a constant stream of new target release dates such that at no point does it appear there is enough time or resources to change the software plan. Result is when it finally goes out it has old software. In this scenario the software vendor has done their job, and it's even possible that the worst the product owner has done is to fail to foresee the unforseeable, depending on what caused the product slip.

    Again, the point is not that I think this is what happened, but rather that what actually happened is most likely more complicated than it might seem and largely unknown to us.
     
  11. Dec 29, 2005 #51 of 118
    dswallow

    dswallow Save the ModeratŠ¾r TCF Club

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    I believe it was shown running the 6.x software at CES last year.

    Not that it matters much; obviously sooner or later it's a dead end product anyway. It's serving its purpose well for the time being, even if sometimes a little slow on the menus.
     
  12. Dec 29, 2005 #52 of 118
    bdlucas

    bdlucas Right side up again.

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    This gives us but a tiny window into what's going on. I can attest from personal experience that trade show demos bear only a loose relationship to products. (Reminds me of the old joke about the guy who dies, and is given a choice between heaven and hell. He's shown a video of hell: dancing, wine, partying, a generally good time. He's shown pictures of heaven: peaceful enough but boring. Of course he chooses hell. But on arrival he finds something quite different: fire, brimstone, eternal suffering. What's up, he asks? Where's the party? Oh, comes the answer; you must have seen our demo. :))

    Quite possibly one of the complicating factors in the story. Resources are only reluctantly committed to dead-end products. DirecTV may even have known before its release that it was a dead-end product, and TiVo may have know that it was a dead-end relationship.
     
  13. Jan 25, 2006 #53 of 118
    newsposter

    newsposter Poster of News

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    Can anyone else answer this now that we are closer to the hd dvr than ever? :)
     
  14. Jan 25, 2006 #54 of 118
    AbMagFab

    AbMagFab What happened, TiVo?

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    By definition, we are always closer than ever. But that means we're still 6-12 months away.
     
  15. Jan 26, 2006 #55 of 118
    newsposter

    newsposter Poster of News

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    Now I have another 'weird' question for you. Are the SD programs any better than in MPEG2 when watched on the HD channel? I prefer to watch SD stuff OTA with bars as the colors and textures are so much better than directvs locals. So I was wondering, did the SD locals programs improve when you watch them on the directv HD channel and get the same results as i'm getting today with OTA SD?

    hope i was clear..gets confusing with all those abbreviations
     
  16. Jan 26, 2006 #56 of 118
    kdonnel

    kdonnel DVC-BCV

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    Are they actually watchable? Two of my neighbors and another friend have all upgraded to the H20. According to all three of them the HD locals from DirecTv are all but unwatchable.

    They have all had DirecTV out to replace the LNB, run new cabling, and repoint the new dish. In each case the picture still pixelates all the time.

    They have been told it was their TV, it is a software problem DirecTV is working on, and that DirecTV has no idea why it does not work but they are trying to figure out why.
     
  17. Jan 26, 2006 #57 of 118
    jcricket

    jcricket New Member

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    To answer the poster's original question, I think Earl commented over at dbstalk.com that he couldn't see the difference between the MPG4 HD Satellite locals and OTA HD locals (MPG2) viewed on the on the H20 receiver (not a DVR, but that doesn't matter).

    I can certainly tell the difference between SD programs on my OTA local channels and MPG2 Satellite versions of those local channels (on my HR10-250). However, when I compare general quality of Discovery HD and an OTA local, they appear about the same. Quality of programming itself is a different matter :)

    I'm willing to bet that the MPG4 HD locals will be high enough quality that it will be a good-enough solution for most people when compared to having to deal with an OTA antenna and uncertain reception. There will continue to be some people who can see a difference, either because they just hate the idea of re-compression or have some uber high-end setup where differences are obvious. Most of us will be happy to get all our programming via the satellite and go back to not having to deal with the whole antenna situation.

    Whether or not the HR20 is better than the HR10 is another matter too.
     
  18. Jan 26, 2006 #58 of 118
    spdntckt

    spdntckt New Member

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    I cant compare the HD DVRs.. but i can tell you that as a technology, a 15-18mb/s MPEG 2 picture is better - by far - than a 10mb/s H.264 MPEG4 picture - at least on the encoders ive used..
    Reference /input was an 8 bit uncompressed 1920x1080i signal.. approx 1000mb/s bandwidth
    display device is a sony VPL-VW100 1920x1080i projector - 1080p capable. Input was

    Reference signal was than passed into a few encoders, the best was Apple's compressor which was configured for MPEG2- open GOP of 8, data rate 18mb/s - 1280x720p - this is test case 1

    test case 2 was the same Apple compressor, configured for H.264 at 10mb/s, MPEG4, resolution 1280x720p

    When viewed on the large (7') screen, everyone i showed it to could see the difference. MPEG2 was clearly the 'better picture'

    MPEG4 is 'damn good' considering it is almost 1/2 the bandwidth.. but for overall picture quality a high b/w MPEG2 source is better.. most of the encoder videophiles agree that high b/w mpeg2 is better than mid b/w MPEG4.. however, bit for bit.. MPEG4 will be better (eg. you cant compare a 10mb/s MPEG2 and MPEG4 source.. mpeg2 is only better at higher bit rates).
     
  19. Jan 26, 2006 #59 of 118
    bdlucas

    bdlucas Right side up again.

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    I think the last bit is the key, since the quality of the encoder is critical to the results. Reports I've seen say that both by objective and subject tests, MPEG-4 H.264 is capable of equally quality to MPEG-2 about half the bitrate. Reports on this forum comparing OTA MPEG2 to DirectTV MPEG4 seem to agree.
     
  20. Jan 26, 2006 #60 of 118
    SpankyInChicago

    SpankyInChicago New Member

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    Well, unless DirecTV is getting the raw SDI datastream from the OTA station (unlikely), what DirecTV is actually doing in recompressing an already compressed picture.

    If DirecTV is getting the same MPEG2 stream from the OTA station that we can pick up with our OTA antenna, it would be impossible for any signal sent by DirecTV to us over the satellite, whether further encoded with MPEG2 or reencoded with MPEG4 to look as good as the original OTA signal.

    Further lossy compressing an already lossy compressed signal always looks worse than the original lossy compressed signal regardless of the secondary lossy compression method used.
     

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