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Watch four tuners at once?

Discussion in 'TiVo Premiere DVRs' started by redbeard25, Feb 3, 2013.

  1. redbeard25

    redbeard25 Member

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    Jan 15, 2002
    This probably shows a bit of ignorance on my part, but here goes...

    In Live TV, could Tivo have a mode where you can see all four tuners on your screen at once, kind of like DirecTV does with their "Mix" channels?

    They could label them A, B, C, D and you could use those buttons on the remote - press once to select for trick play and hear the sound, twice for fullscreen.

    Is there an engineering reason why they couldn't?
     
  2. compnurd

    compnurd New Member

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    Oct 6, 2011
    Mix Channel on Direct TV is a channel for them... It is not using multiple tuners on the box
     
  3. aaronwt

    aaronwt UHD Addict

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    Northern...
    You would need a decoder for each stream you are watching. So you would need four to watch four tuners simultaneously. The TiVo only has one MPEG decoder.
     
  4. unitron

    unitron Active Member

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    semi-coastal NC
    If you're quartering the screen and putting up 4 smaller versions of each stream that's being tuned, one decoder would be enough if it was fast enough and you had the software to send it the first line of the first channel, then the first line of the second, then the first line of the third, then the first line of the fourth, then the second line of the first, etc.
     
  5. aaronwt

    aaronwt UHD Addict

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    The TiVo isn't designed for that.
     
  6. unitron

    unitron Active Member

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    semi-coastal NC
    But if the single MPEG decoder was fast enough, it could be.

    Hence my use of the word "If" in my previous post.

    Not that I expect them to bother to design one that way to provide a feature that only a handful of owners would ever bother with on a regular after the novelty wore off basis.
     
  7. Dan203

    Dan203 Super Moderator Staff Member TCF Club

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    Nevada
    That wouldn't work. MPEG-2 uses temporal compression, meaning frames are built using information from the frames around them. Basically one frame is only encoded with the information that makes it different from the previous frame. Not only that but the encoded order of the frames is not the same as the display order. Because of this the decoder has to maintain buffers of the reference frames. There is no way a single decoder could switch back and forth between 4 different streams without flushing those buffers and making it impossible to decode subsequent frames. The only way they could do this is if they decoded an entire GOP at a time. In MPEG-2 the average GOP is about 1/2 second so they would need a minimum 2 second delay to display 4 streams, plus the overhead of buffering to disk, display, etc... So probably about 5 seconds total. With H.264 however it becomes a LOT trickier. There aren't really GOPs in H.264. And there can be 10+ seconds between safe entry points in an H.264 stream. So if they tried the same trick they'd likely have to put a huge delay in and even then there is a high likelihood that there would be a lot of artifiacts and decoding errors in the video as you watched.

    Dan
     
  8. unitron

    unitron Active Member

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    See, I told you analog is better. :)
     
  9. Dan203

    Dan203 Super Moderator Staff Member TCF Club

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    It's not a direct conversion but an uncompressed 4:2:0 1080i analog signal would require an equivelent of about 750Mbps of bandwidth. Use something like motion JPEG or I frame only MPEG-2 and you can cut that down to about 50Mbps. The average MPEG-2 stream broadcast by your cable company is about 14Mbps and H.264 streams are about 1/2 that. So you can understand why they use digital formats with temporal compression over analog. A slight loss of perceived quality and loss of a little flexibility in decoding can result in massive bandwidth savings.

    And when we eventually transition to 4K that compression is going to be even more important. 4K requires about 3.4x as much bandwidth as 1080i when encoded with those same codecs. That's why the industry is pushing towards H.265, it's supose to cut bitrates by about 1/2 again compared to H.264 which will make up for a good chunk of that jump. Basically you'll be able to get 4K resolution in the same bandwidth currently used for MPEG-2 streams.
     

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