DVD Spin Rates and Scan Direction

Discussion in 'Archived Threads 2001-2004' started by Doug_L, Aug 27, 2002.

  1. Doug_L

    Doug_L Stunt Coordinator

    Jun 22, 2000
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    This is really more of a hardware question, but I figured I'd pose it here and if I'm way off base an admin will just up and move it.

    I have a series of questions about how DVD players spin and read discs:
    1) Does the player begin reading at the outer, or inner edge of the disc?
    2) Does the disc spin at a constant rate, or a variable rate?
    3) Similarly, does a single frame of information on the outer edge use the same amount of memory/space as the same frame would on the inner edge?

    All of the above questions arose out a discussion of Laserdiscs and CAV vs. CLV. While we're at it, if somebody could confirm my LD understanding that would be great. As I remember it, LD's spun the disc at a constant speed when the disc was CAV (constant angular velocity) and changed the spin rate for CLV (Constant Linear Velocity). CLV was a much more efficient storage system, though, as a single frame took up the same amount of space regardless of it's location on the disc. CLV disc could not be played in slowmotion, or step motion though, as I remember, although there are probably players that can do this by now.

    I hope somebody can answer my DVD questions and confirm or correct my LD assumptions. Thanks in advance.
  2. Ken Chan

    Ken Chan Producer

    Apr 11, 1999
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    Inner to outer. Most dual-layer discs are RSDL (Reverse Spiral Dual Layer), so they go inner to outer, then back to inner.

    The discs are effectively CLV, but the drives can spin at a constant velocity and use buffers. The location of frames (inner or outer) doesn't matter, but in MPEG, there's a fairly constant distribution of bigger (full) frames and smaller (interpolated) frames.

    Your notions of LDs are correct, except that the last few generations of players had digital memory to do the effects on CLV discs.


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