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CentOS 7.0 - man page for gsm_option (centos section 3)

GSM_OPTION(3)			     Library Functions Manual			    GSM_OPTION(3)

NAME
       gsm_option -- customizing the GSM 06.10 implementation

SYNOPSIS
       #include "gsm.h"

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

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

       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 algo-
       rithm  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 sam-
       ples for purposes of finding that correlation, and hence speeds up the encoding at a noti-
       cable 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  ver-
       sion 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).

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

BUGS
       Please direct bug reports to jutta@cs.tu-berlin.de and cabo@cs.tu-berlin.de.

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

										    GSM_OPTION(3)


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