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       gsm_option — customizing the GSM 06.10 implementation


       #include "gsm.h"

       int gsm_option(handle, option, valueP);
       gsm handle;
       int option;
       int * valueP;


       The  gsm  library  is  an  implementation  of the final draft GSM 06.10
       standard for full-rate speech transcoding, a lossy  speech  compression

       The  gsm_option() function can be used to set and query various options
       or flags that  are  not  needed  for  regular  GSM  06.10  encoding  or
       decoding, but might be of interest in special cases.

       The  second  argument  to gsm_option specifies what parameter should be
       changed or queried.  The third argument is either a  null  pointer,  in
       which  case the current value of that parameter is returned; or it is a
       pointer to an integer containing the value you want to  set,  in  which
       case the previous value will be returned.

       The following options are defined:

       GSM_OPT_VERBOSE Verbosity level.
              This  option  is only supported if the library was compiled with
              debugging  turned  on,  and  may  be  used  by   developers   of
              compression algorithms to aid debugging.
              The  verbosity  level can be changed at any time during encoding
              or decoding.

       GSM_OPT_FAST Faster compression algorithm.
              This implementation offers a  not  strictly  standard-compliant,
              but  faster  compression  algorithm  that is compatible with the
              regular method and does not noticably degrade audio quality.
              The value passed to
                   gsm_option(handle, GSM_OPT_FAST, & value)
              functions as  a  boolean  flag;  if  it  is  zero,  the  regular
              algorithm will be used, if not, the faster version will be used.
              The availability of this option depends on the hardware used; if
              it  is not available, gsm_option will return -1 on an attempt to
              set or query it.
              This option can be set any time during encoding or decoding.

       GSM_OPT_LTP_CUT Enable, disable, or query the LTP cut-off optimization.
              During  encoding,  the  search for the long-term correlation lag
              forms the bottleneck  of  the  algorithm.   The  ltp-cut  option
              enables an approximation that disregards most of the samples for
              purposes of finding that correlation, and hence  speeds  up  the
              encoding at a noticable loss in quality.
              The value passed to
                   gsm_option(handle, GSM_OPT_LTP_CUT, & value)
              turns the optimization on if nonzero, and off if zero.
              This  option can be set any time during encoding or decoding; it
              will only affect the encoding pass, not the decoding.

       GSM_OPT_WAV49 WAV-style byte ordering.
              A WAV file  of  type  #49  contains  GSM  06.10-encoded  frames.
              Unfortunately,  the framing and code ordering of the WAV version
              are incompatible with the native ones of this GSM 06.10 library.
              The  GSM_OPT_WAV49 option turns on a different packing algorithm
              that produces alternating frames of 32 and 33 bytes (or makes it
              consume alternating frames of 33 and 32 bytes, note the opposite
              order of the two numbers) which, when concatenated, can be  used
              in the body of a WAV #49 frame.  It is up to the user program to
              write a WAV header, if any; neither the library itself  nor  the
              toast program produce complete WAV files.
              The value passed to
                   gsm_option(handle, GSM_OPT_WAV49, & value)
              functions as a boolean flag; if it is zero, the library’s native
              framing algorithm will be used, if nonzero, WAV-type packing  is
              in effect.
              This  option  should  be  used  before  any  frames are encoded.
              Whether or not it is supported at all depends on a  compile-time
              switch,  WAV49.   Both option and compile time switch are new to
              the library as of patchlevel 9, and are considerably less tested
              than the well-worn rest of the it.
              Thanks  to  Jeff  Chilton  for the detective work and first free
              implementation of this version of the GSM 06.10 encoding.

       GSM_OPT_FRAME_CHAIN Query or set the chaining byte.
              Between the two frames of a WAV-style encoding,  the  GSM  06.10
              library  must  keep  track  of one half-byte that is technically
              part of the first frame, but will be written as the  first  four
              bits  of the second.  This half-byte are the lowest four bits of
              the value returned by, and optionally set by,
                   gsm_option(handle, GSM_OPT_FRAME_CHAIN, & value)
              This option can be queried and set at any time.

       GSM_OPT_FRAME_INDEX Query  or  set  the  current  frame’s  index  in  a
       format’s alternating list of frames.
              The WAV #49 framing uses two alternating types of frames.  Which
              type the next GSM-coded frame belongs to  can  be  queried,  or,
              when decoding, announced, using
                   gsm_option(handle, GSM_OPT_FRAME_INDEX, & value)
              For  WAV-style  framing,  the  value should be 0 or 1; the first
              frame  of  an  encoding  has  an  index  of   0.    At   library
              initialization, the index is set to zero.
              The  frame  index  can  be queried and set at any time.  Used in
              combination with the GSM_OPT_FRAME_CHAIN, option, it can be used
              to position on arbitrary GSM frames within a format like WAV #49
              (not accounting for the lost internal GSM state).


       gsm_option() returns -1 if an option is  not  supported,  the  previous
       value of the option otherwise.


       Please  direct  bug  reports  to and cabo@cs.tu-


       toast(1), gsm(3), gsm_explode(3), gsm_print(3)