Just Found My Dvd Player Has Bitrate Counter What Is This

Discussion in 'Blu-ray & DVD Players & Recorders' started by bigjonnyauk, Sep 16, 2003.

  1. bigjonnyauk

    bigjonnyauk
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    HI ALL

    just messing with my tosh dvd player while watching a film and came across a bitrate counter going up and down, what does this actually mean

    is this the sound or pic or what


    what is good and whats not so good kept moving between 4.0 and 10.0

    ????????????????????????????????
     
  2. timlloyd

    timlloyd
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    bigjonnyauk

    This is the mpeg bitrate that the film was encoded at, at any particular time, think the dvd standard has a maximum of 10 Kbs. You should find scenes with action / movement the bitrate will be higher.

    Tim
     
  3. bigjonnyauk

    bigjonnyauk
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    ahhh right yeah just watched bulletproof monk(not the best film i ever seen) and it kept incresing to 10 when fighting
     
  4. Garrett

    Garrett
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    If I remember all those years back when I was told what it was is how much information is coming of the DVD at a point to make that picture up. As the space is restricted on a DVD they do not up rate pictures that stand still or parts of background that stay still e.g. in the old cartoons you only had a still background and moved your characters across the front which helped you're to not keep drawing the background every time.
    As timlloyd says the bit rate will go up on action and movement, because it is upgrading more of the picture.

    Which model of Toshiba is it?
     
  5. bigjonnyauk

    bigjonnyauk
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    oh its not a top of the range jobby just a sd220 but i really am happy with it picture wise i even bought a second for the bedroom lol
     
  6. vonhosen

    vonhosen
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    Technical Info

    As already stated this is the bitrate for the MPEG stream on the disc. The ouput is in Mbs, upto maximum of 9.8Mbs & is for video & audio combined.

    MPEG uses temporal compression. This means that one frame can use info from another frame (provided that info has changed little or not at all) to save space. But so that the MPEG stream can be decoded without having to reload all the stream into memory it limits this compression into small groups of pitcures (GOPs).

    For PAL the maximum number of frames in a GOP is 15, for NTSC the maximum is 18 (you can have less). These frames are called I , B & P frames.

    "I" frames are compressed independantly (rather like JPEGs) They therefore contain relatively a lot of bits (taking up more room) & are good for frames that contain a lot of change/movement.

    "P" frames save space by being based on previous "I" & "P" frames

    "B" frames are based on past & future "I" & "P" frames & offer best compression.

    A Typical PAL GOP will look like this " IBBPBBPBBPBBPBB "

    When encoding you can use a Constant Bitrate for the stream or , more usual with commercial discs, a Variable bitrate. Variable bitrate is what you are seeing & is used to save space. the encoder will do multiple passes of the file, first reading it to see where the most compression can be used (where there is little action or change). It can then save space for where a higher rate is needed (for higher degree of action or change). On a later pass the encoder will then encode.

    Hope that helps
     
  7. Easy2BCheesy

    Easy2BCheesy
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    That's a very good explanation, but I believe that extra I frames can be inserted at any time in a GOP. This is required to prevent pixelisation/artefacts when a scene cuts to another, when there's strobe-lighting etc. Chapter points on a DVD can only be located on an I frame.
     
  8. vonhosen

    vonhosen
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    Indeed

    Some encoders can
    1) Force "I" frames so that you can get the exact frame for chapter point you require (rather than being 1/2 sec out). It is not enough to just force an "I" frame though. It will also need the creation of a new GOP because the chapter point has to be on a GOP header boundary not just an "I" frame.
    2) Insert "I" frames automatically at scene changes.
    3) Segment encode (So that you can tailor the encode for particularly difficult scenes)
     

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