What is transmission bitrate?

Discussion in 'Archived Threads 2001-2004' started by Evelio Lucero, Aug 16, 2002.

  1. Evelio Lucero

    Evelio Lucero Auditioning

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    My Pioneer DV533K is able to display the transmission bitrate at any particular time while a disc is being played. This displayed value changes as the disc play progresses.

    I hope someone can help with the following questions:

    1. What is transmission bitrate? Is this the sum of the audio transmission bitrate and the video transmission bitrate?
    2. I know that basically the bitrate is one of the factors considered in defining picture quality. What value is considered necessary for a good quality picture? Do the Superbit titles show this ideal bitrate value? Is it always true to say that a low bitrate translates to poor picture quality?
    3. I realize that the there is a conscious tradeoff being taken between high bitrate and the amount of data content (special features, subtitles, audio tracks, etc.). What exactly do they do when they minimize the bitrate to squeeze in more material into the disc? Doesn't every pixel on the screen have to be accounted for? If every pixel on the screen represents data to be transmitted, shouldn't my dvd player show a constant bitrate at any point in the disc?
    4. I've seen some forum postings that refer to an average bitrate for a film. How did they arrive at this? My Pioneer player does not have an average bitrate for a disc. Neither does it display the film's filesize that would have allowed me to compute an average bitrate using the films running time.
    5. Finally, what is the acceptable bitrate for DD5.1 and DTS? What is half-bit DTS bitrate?

    I'd truly appreciate any help.
     
  2. Vince Maskeeper

    Vince Maskeeper Producer

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    DD and DTS have fixed bitrates that do not vary. DD comes in several bitrate varieties, the most popular being 384kbps and 448kbps (most stereo titles are encoded at 192kbps).
    DTS originated as a 1509 kbps stream in the theatrical environment, which was slightly reworked for the home (but stayed at 1509). When DVD came along, a truncated version of DTS was developed with a bitrate of 754kbps.
    But again, the idea of bitrates is often overused if not misused... the concept is misunderstood and does little to tell you what you will hear or see.
    I suggest if you're interested in some of the more technical elements of DD and DTS, check ou this document:
    http://home.clear.net.nz/pages/adbarr/page1.html
    -vince
     
  3. Geoff S

    Geoff S Stunt Coordinator

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    For reference, From a DVD the combined audio+video bitrate ranges from 3.5 m/bits per second minimal all the way to 10.08 m/bits per second.

    The most common places you will find high bitrates are scenes hard to compress in MPEG 2, such as nighttime scenes, or scenes with moving water or lots of movement and changing colors. Notice in the Titanic DVD the end of the movie rarely slips below 8 m/bits per second as an example (night and water).
     

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