OTA HD vs HD Locals on Cable

Discussion in 'TiVo Series3 HDTV DVRs' started by Zaph32, Oct 2, 2007.

  1. Oct 2, 2007 #1 of 11
    Zaph32

    Zaph32 New Member

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    Has anyone done a quantitative comparison between the same channels when delivered via antenna or via HD cable?

    I realize this may vary by provider, but is it normally the same exact bitstream?

    I compared stills between my HD locals on antenna and cable (Time-Warner, Dallas) and couldn't see a difference.

    I am curious what other people think.
     
  2. Oct 2, 2007 #2 of 11
    MickeS

    MickeS Active Member

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    I have seen some comparisons, most were unfavorable for the cable versions.

    I did some myself, but that was between OTA and cable in two different markets:
    http://www.tivocommunity.com/tivo-vb/showthread.php?t=365231

    The OTA bitrate for NBC I had was around 35% higher than the cable bitrate I have here. And it's VERY noticeable.
     
  3. Oct 2, 2007 #3 of 11
    moyekj

    moyekj Well-Known Member

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    FYI, OTA if you can get good signal strength is always a better option than the cable carriage since there is no chance it can undergo bit-rate shaping which most cable companies employ (as part of the technology that stuffs multiple channels in a QAM 256 modulation scheme into a fixed 6MHz bandwidth limit). Having said that there is very little visual difference I notice on my 47" 1080p LCD of OTA version versus cable version for my headend, but I like the peace of mind OTA provides that I'm getting the best possible version in my local market.
     
  4. Oct 2, 2007 #4 of 11
    astrohip

    astrohip Well-Known Raconteur TCF Club

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    I have Comcast Houston, and recently installed an antenna because of the pixellation problem (I have terrible pixellation with ABC/NBC HD on the cable feed). So I can compare an OTA vs cable feed. First, I can tell you the OTA is as crisp as cable, maybe more. I did some A/B comparing--put ABC OTA on tuner 1, ABC cable on tuner 2--and watched some hi-def football, and the OTA looked better, but only slightly. Did it later that day with some golf on NBC (or was it CBS?). Again, OTA was slightly better.

    I haven't been able to actually compare files sizes yet, as my tuners are working overtime with all the new shows. I literally don't have a prime time slot where I can free up both tuners to compare.

    Once I figure out what new shows I *don't* want to keep as SPs, I can play around a little more and get some hard data. I actually did compare one show, but I think it was local news. The OTA was only about 3-5% bigger. But I figured this may not have been the best comparison, as I don't know how news normally sizes out.

    I'll bookmark this thread, and report back in a week or two.
     
  5. Oct 2, 2007 #5 of 11
    Revolutionary

    Revolutionary Too sleepy for TV...

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    astrohip, your case is closed. If the same program recorded from both sources differed in size, then it differed in bitrate. It doesn't matter "how news normally sizes out" (granted, I have no idea what you mean by that, but it wouldn't matter--nothing it means could matter). If the same number of minutes/seconds took up less space in one of the recordings, then that recording has a lower rate of bits per second. And a lower bitrate means lower quality. That it is the exact same program seals it: there is no other variable.
     
  6. Oct 2, 2007 #6 of 11
    moyekj

    moyekj Well-Known Member

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    I haven't done it but I could also record OTA version of a show on 1 tuner and the cable equivalent on the other on 1 of my S3s and then check Info to compare sizes - that's a pretty easy way of comparing the two. Note that this is only telling of bitrate differences if there is a pretty large discrepancy between them. Note that OTA version may contain additional PSIP data not available via cable version so I would expect OTA version to be a little bit larger even if there is no bitrate shaping. I would say if both sizes do not differ by more than 5% or so I wouldn't be at all concerned.
     
  7. Oct 2, 2007 #7 of 11
    aaronwt

    aaronwt UHD Addict

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    Here they are the same. OTA looks the same as Comcast which looks the same as FIOS. The same program recorded from all 3 sources is basically the same size.
     
  8. Oct 3, 2007 #8 of 11
    astrohip

    astrohip Well-Known Raconteur TCF Club

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    My ability to mangle the English language is only limited by my time. :)

    I think what I meant was maybe news has a different cable compression setting than prime time shows or sports. Maybe not. I will confirm over the next couple days with some hard testing.
     
  9. Oct 3, 2007 #9 of 11
    TexasGrillChef

    TexasGrillChef New Member

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    I am with TWC in Dallas as well.

    My 65" has Picture beside picture... effectively 2 same size pictures on screen at same time. When I did a comparrison of OTA Vs same channel (HD) as TWC... picture quality appeared to be the same.

    However, I did notice some caveats.... When we are having bad storms, The picture quality seemed better (No pixelation) on cable than with OTA which has lots of pixelation during the bad storms.

    BTW I have a big antanae in my atic running directly to the built in ATSC tuner in my TV.

    I think it all varies with the area your in, & your cable provider. There are parts of TWC still using the older cable head ends/systems in the dallas area. Especially in areas of Farmers branch, Carrollton & Plano/richardson.

    TGC
     
  10. acvthree

    acvthree Active Member

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    I did a visual camparison for OTA vs. Fios.

    Previously, I had DirectTV and there was a huge difference with OTA being better.

    With Fios, I recorded two HD shows, ran them up to the same point and did a very critical inspection of the picture quality. It was still OTA but by a, ahem, photo finish.

    This is with a large antenna in the atic.

    It was not enough difference if I did not already have the antenna set up, but I still record OTA for locals and network.

    I didn't think about checking the recording size. I'll check that out sometime.

    Al
     
  11. Cyrl

    Cyrl New Member

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    Pittsburgh, PA
    Most providers recompress hd channels to some degree due to bandwidth issues, OTA feed should (if you get a clean signal) always be equal to or better than the rebroadcast version, though weather can really play havoc with that. I think the original HD feeds are like 17-19mbit/sec which starts to get really prohibitive for the cable/sattelite/fios etc co's when customers want lots and lots of channels.
     

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