Is MPEG2 always a component signal?

Discussion in 'Archived Threads 2001-2004' started by Keith Mickunas, Jan 16, 2003.

  1. Keith Mickunas

    Keith Mickunas Cinematographer

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    I was having a discussion tonight with Vincent Yeh and the issue came up as to what the best connections with a Tivo are. I've heard that with satellite, the MPEG2 is a compressed component signal, so its best to use S-Video out. I believe Tivo uses MPEG2 also, so would that too be a component signal, or is it possible to compress composite video with MPEG2? Also, what about digital cable? I'm fairly certain the digital channels use MPEG2 for compression, would those be decompressed as component?

    I've got my system set up where the satellite's s-video goes to the receiver and the composite goes to the Tivo. Then the Tivo connects to the receiver via s-video, and I run a single s-video to my TV (a Mits 55411 HDTV). Personally I see very little degradation when switching between the Dish's s-video and the tivo, so I probably won't change anything. I'm going to hook up a composite video to the tivo also soon just to see, but I'm wondering if anybody knows how the Tivo (and satellite/digital cable) really works.
     
  2. VincentY

    VincentY Stunt Coordinator

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    my setup here in manhattan is:
    standard definition dedicated cable box 2100 Scientific Atlanta/Time Warner for my Tivo Series 2 to my TV. Wall coax to my cable box, tried S-Video from cable box to Tivo and S-Video to tv, horrible picture (but one of the two S-Video cables is a freebie from Tivo = bad quality).
    Then, i tried composite from cable box to Tivo and composite from Tivo to TV (both composites are Kimber V-21), wow, what a difference!
    So i'm trying to find out if the change has to do with bypassing the comb filter of the Tivo by using composite in and out, or it has more to do with my cables? The other thought is that if i had used far better quality S-video cables into Tivo and out to my TV, maybe the results are different despite the fact that S-video probably means the use of the comb filter (probably of an inferior quality) in the cable box.
    by the way, the tv is a 60xbr800 LCD RPTV.
    thanks.
    my direct email is: [email protected]
     
  3. Bob McElfresh

    Bob McElfresh Producer

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    I believe DSS/MPG2 is seperated video (SVideo). But unlike a DVD, many cable/network shows have fairly low-quality video before it gets to the sat facility.
    Flipping from Composite to SVideo on a DVD is a visible improvement. But hooking both up from my DSS system - much less difference. (I was comparing a local network station via CATV to DSS-Composite and DSS-SVideo. Yes, I have too much time on my hands. [​IMG] )
    Where SVideo really shines with a DSS system is the text and horizontal/vertical lines on the program guide. And since you use this a lot, it's really worth using SVideo.
    If you try to compare Composite & SVideo with programming - use a premium station like an HBO channel.
    Hope this helps.
     
  4. Keith Mickunas

    Keith Mickunas Cinematographer

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    So Bob if you're correct that would mean that it would mean its always best to use S-Video out from the Tivo, right? Since you mentioned text, that gives me an idea. I'll see how the Tivo's menus look between composite and s-video. That'll tell me how good my TVs comb filter is at least. I'll also try looking at CNN or something similar with lots of scrolling text.
     
  5. Scott Kimball

    Scott Kimball Screenwriter

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    The video compression and the interconnects are two unrelated issues.

    Widely available digital video is in MPEG2 format: DVD, DSS, cable, in-box TIVO compression, etc.

    You don't need to know what format the video is in... just use the best quality interconnects on your equipment to get the best picture.

    From best to worst:
    Component
    S-Video
    Composite
    RF

    The entire signal path must use the same interconnect, so if your DVD player is hooked to your A/V receiver with s-video, but your receiver is hooked to your TV with composite - if you get any picture at all, it will be with quality equal to the worst of the two interconnects.

    With a lower quality input, such as an overcompressed satellite channel, the improvements of the higher quality interconnects are going to be less apparent.

    -Scott
     
  6. Keith Mickunas

    Keith Mickunas Cinematographer

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    No, it does matter. The signal carried by S-Video and Component cables is a component signal, whereas that carried by composite cables and analog cable TV is a composite signal. A composite signal can be converted to a component signal by running it through a comb filter, but its still preferable to deal with the component signal if that's how it originated.

    If the Tivo's MPEG2 implementation uses a component signal, then its best to feed it using S-Video and use S-Video out. That way nothing other than compression on the disc is done to the signal. However if the MPEG2 compresses a composite signal, it would probably be better to use the composite out if the TV has a better comb filter, which I'm almost certain my TV does.
     
  7. Keith Mickunas

    Keith Mickunas Cinematographer

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    I just checked a book on graphics file formats I have which states that the Color Representation for MPEG2 is YCrCb. This is a component signal, which means its probably best to always use S-Video with the Tivo. If you feed it a composite signal, it will be run through a comb filter and converted to YCrCb before being stored as MPEG2 video.
     
  8. Bob McElfresh

    Bob McElfresh Producer

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  9. VincentY

    VincentY Stunt Coordinator

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    Keith: saw what you wrote/researched. yet, in my case, using a dedicated time warner/scientific atlanta 2100 cable box that is only used with the Tivo, using the composite out is far superior from the cable box to the Tivo since the 2100's comb filter is so inferior that it might even be a notch filter! however, it is useful to learn from you that the OUTPUT from the Tivo would most likely be best with S-video since the signal does not need to be "merged" together and have to be separated by my Sony TV's comb filter again, no matter how good my Sony TV's comb filter is.

    am i understanding this correctly for my particular situation?

    thanks!
     
  10. Keith Mickunas

    Keith Mickunas Cinematographer

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    Yes that does sound best for you Vincent. Cable boxes are often pretty cheap, so I'm not surprised the comb filter is weak, in fact I'm surprised it even has S-Video.

    One thing to note though. If you have digital cable, some channels might be better using the S-Video output. With some cable systems, and I know its the case in Plano with AT&T, if you buy the digital cable package, certain channels are digital, while the lower channels that come with the cheaper packages are still analog. Now the digital channels will be MPEG2, so in theory those channels will be better out of the S-Video. But I'd recommend sticking with the composite because the majority of time you'll be better off that way.
     
  11. VincentY

    VincentY Stunt Coordinator

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    Keith:

    will the digital channels still be "forced" to go through the comb filter/notch filter? or is the cable box smart enough to know that the digital channels should be simply "pass through" and only the analog channel channels go through the comb/notch filter?

    also, how would one find out which channels are digital and which are not?
     
  12. Keith Mickunas

    Keith Mickunas Cinematographer

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    I would think since it has separate tuners/decoders for the analog and digital sections it'd be smart enough to do it right, but I can't say for sure. My digital cable box didn't have S-Video out, and it had a Dolby Digital logo on it but no digital output, so it had issues.

    As for figuring out which channels are digital, take a look at your cable companies plans. With some there are one or two tiers of programming available before spending the big bucks on digital. Those tiers are analog and can be tuned in by any tuner, not just a cable box (most of the time). Anything available in those tiers will be analog even for the digital cable customers, channels only available to digital cable customers will be digital. Now that's the way Comcast in Independence, MO and AT&T in Plano, TX do it, I can't say all cable companies do it that way.

    Another way to tell is look at the quality. If you see digital compression artifacts, espically blockiness in dark scenes, that channel is digital. Also if you ever see the image break down into a series of boxes, either due to an interruption in service, or while changing channels, its digital. This could happen because the cable company is receiving a digital feed, but most of the time its the fault of the cable company. They overcompress the signals to fit as much as they can, and it reduces the overall quality. Dish Network does this on the locals also.
     
  13. Allan Jayne

    Allan Jayne Cinematographer

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    Using the S-video or component video output:
    Digital channels don't go through any comb filter.
    Analog channels must go through the (usually inferior) cable box comb filter.
    Using the composite video output:
    Analog channels skip the cable box comb filter and go through the TV comb filter. Usually better than the cable box comb filter.
    Digital channels don't go through the cable box filter but must go through the TV comb filter. Not as good as using S-video or component video.
    Most A/V receivers allow you to connect both composite and S-video (and audio) cables from the cable box to the same input bank, while the composite and S-video outputs from the receiver (or directly from the cable box) have to go to differetn input banks of the TV.
    Video hints:
    http://members.aol.com/ajaynejr/video.htm
     
  14. VincentY

    VincentY Stunt Coordinator

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    Allan,

    So what is your practical suggestion, please?

    I have a 2100 Time Warner/Scientific Atlanta standard definition box dedicated to my Tivo Series 2.

    My second cable box is the 3100HD Time Warner/Scientific Atlanta for real time high definition and real time standard definition viewing. So for this box, I need component output to my TV for viewing high definition channels, and EITHER S-video or composite for standard definition channels (otherwise, if I were to use component for all channels, the standard definition channels viewed with component outs has a black margin all around the picture).

    Thanks!
     

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