Main Concept MPEG1 - allows non-NTSC 720x480 ???

Discussion in 'Amateur Video Production' started by lifeson, Oct 3, 2004.

  1. lifeson

    lifeson Guest

    In the Main Concept export settings, the display size by default is
    set to the same size as my input AVI DV captured file - at 720x480.
    This far exceeds the NTSC standard max display size for MPEG1, which
    is 352x240.

    I went ahead and made the video to see if it would work, and it did,
    and I was able to play it just fine. Is this "max" display size of
    MPEG1 just something that is written in the standards - and not an
    actual max at all?
     
    lifeson, Oct 3, 2004
    #1
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  2. lifeson

    Jukka Aho Guest

    See <http://bmrc.berkeley.edu/frame/research/mpeg/faq/mpeg1.html>
    and the section titled "Can MPEG-1 encode higher sample rates than
    352x240x30?". It says, and I quote:

    "Yes. The MPEG-1 syntax permits sampling dimensions as high as
    4095 x 4095 x 60 frames per second. The MPEG most people think
    of as "MPEG-1" is actually a kind of subset known as Constrained
    Parameters Bitstream (CPB)."

    (The fiqures quoted seem to be a bit off. Maybe I am wrong and
    someone will correct me, but I would _believe_ the correct number
    is 4096, not 4095.)

    One of the obvious drawbacks of using MPEG-1 for full-frame 720×480
    video is that (unlike the MPEG-2 format) MPEG-1 does not have any
    special support for interlaced video.
     
    Jukka Aho, Oct 3, 2004
    #2
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  3. I like to speculate, so here goes.

    The binary value for 4095 just fits into 12 bits. To go to 4096
    would require going to 13 bits to express the value.

    Nobody wants to deal with 13 bit numbers, especially just to add one
    more value to the data range. (Nobody wants to deal with 12 bit
    numbers either, but that's a whole 'nother story.)

    An alternative could be to encode a data value x as x-1, so 0 means
    1, ..., 4095 means 4096. That gets 4096 into 12 bits, but it doesn't
    let you use data value 0 for a special purpose. Well, it could, by
    making the data value 1 illegal, so its encoded value 0 represents
    the special value. After all, 1x1 is a very small picture :)

    Who knows?
    Gino
     
    Gene E. Bloch, Oct 4, 2004
    #3
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