The contents of the SGI movie file format are not documented.  To
  create and manipulate SGI movie files in your own application, we
  recommend that you use the SGI Movie Library, part of the Digital
  Media Development environment.  This will not only save you work in
  your application, but will ensure that your program remains
  compatible with any revisions SGI makes to its movie file format.

  If you need to manipulate movie files for cross-platform purposes, we
  recommend that you obtain the QuickTime Developer's Option to create
  QuickTime movies which can be used cross-platform.  Additionally,
  if you have the WebFORCE software product, or Digital Media Tools 5.5
  software product for IRIX 5.3, you can create MPEG movies which can
  be used cross-platform.

  See elsewhere in this FAQ for more information on both the Digital
  Media Development Environment and the QuickTime Developer's Option.

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