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SGI movie Frequently Asked Questions (FAQ)
Section - -32- I want to write a program which creates a JPEG- compressed movie file, but I need to control the

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Top Document: SGI movie Frequently Asked Questions (FAQ)
Previous Document: -31- How do I write a program to read and write compressed data to a movie file?
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                compression quality.  How do I do this with the Movie
                Library?
Date: Fri May  3 11:05:05 PDT 1996

  As of IRIX 6.2, there are additional parameters that you can pass
  in to mvAddTrack to control the compression quality: 
  DM_IMAGE_QUALITY_SPATIAL, DM_IMAGE_QUALITY_TEMPORAL, DM_IMAGE_BITRATE.
  Note that not all codecs support all of these parameters.

  JPEG in particular, supports only the SPATIAL setting.

  (Certain Apple codecs support both TEMPORAL and SPATIAL quality 
  settings; CinePak also supports the BITRATE setting.)

  Additionally, you can do the compression yourself (as could be
  done prior to IRIX 6.2): create a movie file with all the appropriate
  image track parameters (see above),  But instead of simply writing
  frames to the movie and letting the Movie Library automatically
  compress the frames for you, you handle the compression yourself.
  
  To do the compression yourself, you open a Compression Library JPEG
  compressor, set the quality factor, and use it to compress each
  frame.  Then you write the *compressed* data to the movie file
  (see above for instructions on how to do this).

  The tools (dmconvert/makemovie/movieconvert) support these settings
  in Digital Media Tools 5.5 (see the first question in this FAQ) and
  IRIX 6.2.

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