Data protocols
  Besides UDF for data.

  There are at least 9 information protocols (including laser disk)
    DVD, VCD, etc. for 'movie' discs.  

    See also 'optical disc' on wikipedia for more disc variations.
 
  Most commercial DVDs use UDF for directory organization, predefined
    directory and file names, and MPEG2 for the video encoding.
   
  Because DVD (laser disc) were originally designed for movies, 
    the movie industry insisted on a number of copy protection schemes
    be included in the technology.

  * Allows read restrictions based on movie ratings.

  * Content Scramble System. DRM/encryption anti-copy scheme.
    40-bit cipher system. 
      Keys on file, disk, and player. Playing software has to decode and
        authenticate keys.    see: DeCSS about breaking this.

      Using data copy commands fail to copy keys, so DVD player and/or 
        software used to 'play' a movie refuses to run.

      DVD-audio uses "content protection for recordable media" 

  * Macro-vision - an earlier anti-copy scheme.
    Added signal spikes in the "Image frame".
      In VCR recorders, it causes distortion in recording.
      In DVD recorders, player actually refused to record.

      Signal ignored/filtered out by older TVs but can confuse newer systems.

  * Code for regions of the world. (DVD region codes)
    Used to prevent cheaper foreign releases from being sold here.
    0. All - uncoded, no flags or all flags.
    1. U.S., Canada, U.S. territories, Bermuda
    2. Western and Central Europe, Japan, South Africa, etc
    3. S.E. Asia
    4. Australia, Mexico, South America, etc. 
    5. Russia, Africa, South Asia (India), etc.
    6. China.

    8. (airlines, cruise ships, etc).
    ALL - all flags set, may or may not work same as 0. 

    Most modern DVD players will allow 5 discs of any region to be
      played, after which it locks to the region of the last played disc.
      * There are region free players, but some DVDs refuse to be played.  
 
  Transmitting movie/TV images.
    Movies 24 frames/sec.
    TV 50,60 frames/sec (interlaced).
  
  Three general analog TV standards
    see : www.high-techproductions.com/pal,ntsc.htm
    NTSC (US)
    PAL 
    SECAM (France)

  Digital 
    wikipedia : Digital terrestrial television
    ATSC (US)
    DVB-T (Europe and Elsewhere)
    DMB (China)
    ISDB (Japan and South America)