Freeview compression rate?

Discussion in 'Freeview & YouView' started by Geoff, Feb 15, 2005.

  1. Geoff

    Geoff
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    How much are signals compressed on freeview compared to the compression applied to a commercial 2hr DVD?
     
  2. army

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    About 2 to 4x more compressed than a dvd.
     
  3. MarkE19

    MarkE19
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    This question has been asked a few times before, and there is no simple answer.
    The compression varies from channel to channel, and then even from program to program on the same channel. Films & sport would tend to be the least compressed as they have lots of fast movement. Programs such as the news and chat shows with little movement can have higher compression without too much loss of quality.

    Mark.
     
  4. sdc395

    sdc395
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    Also, some (all?) of the multiplexes use stat-muxing, dynamically allocating a higher proportion of the available bandwidth to the channels with the trickiest scenes.
     
  5. army

    army
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    Yes i agree bit rates vary alot, channel 5 has the lowest and BBC 1 the highest. However i have yet to copy a film which didn't fit on 1 dvd-r and sometimes you are able to get 2 full length movies onto 1 dvd.
     
  6. matty2767

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    dont forget there is no surround sound either
     
  7. howesey

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  8. howesey

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    Each DVB-T multiplex is 8MHz wide, capable of 24Mbs, 6 channels can be carried down each multiplex.

    The BBC have one multiplex to themselves. So, BBC1, BBC2, BBC Three, BBC Four and BBC News 24 have a share of that 24Mbs.

    ITV1, ITV2, ITV3 and Channel 4 have their own multiplex.

    Five's in the same multiplex as some Top-up TV channels.


    Quite low compare to Sky that runs on DVB-S. 38Mbs, split between 4 or 8 channels, or two HD channels.


    Sky HD will be using DVB-S2, which is around 30% more efficient and can be up to 54Mbs. Also, it will use better codecs (H264 or maybe even VC-1), you'll be ble to get 6 HDTV channels in one streme and you wont notice much difference in compression quality as current Sky.
     
  9. sdc395

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    howesey, the useable bandwidth provided by DVB various significantly depending on the modulation scheme, guard interval and the amount of forward error correction used.

    Also, bandwidth alone does not determine picture quality. In my experience, Freeview's picture quality is as good as, if not better than, Sky's. And it varies from channel to channel and moment by moment, of course.

    Furthermore, BBC FOUR/CBeebies is not on the same mux as BBC THREE/CBBC. Mux 1 only carries four TV channels; BBC ONE, BBC TWO, BBC THREE/CBBC and BBC News 24.
     
  10. nigels0

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    Actually not - Films recorded on celluloid take up a lot less bandwidth because they are frame based (thirty every second) and the MPEG standards have a mode for handling this which significantly cuts down the needed bandwidth. If teh film is digitally recorded, then that is another matter....
     
  11. cerebros

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    Ignoring the fact that film is 24 frames per second, I would say that it's wrong to assume that films would have lots of fast movement - maybe if all you watch are action films...
     

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