gsm_option.3

柏林科技大学开发的gsm编码程序

.\"
.\" Copyright 1992-1995 by Jutta Degener and Carsten Bormann, Technische
.\" Universitaet Berlin.  See the accompanying file "COPYRIGHT" for
.\" details.  THERE IS ABSOLUTELY NO WARRANTY FOR THIS SOFTWARE.
.\"
.PU
.TH GSM_OPTION 3 
.SH NAME
gsm_option \(em customizing the GSM 06.10 implementation
.SH SYNOPSIS
#include "gsm.h"
.PP
int gsm_option(handle, option, valueP);
.br
gsm handle;
.br
int option;
.br
int * valueP;
.SH "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.
.PP
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.
.PP
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.
.PP
The following options are currently defined:
.PP
.I GSM_OPT_VERBOSE
Verbosity level.
.br
.in+5
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.
.br
The verbosity level can be changed at any time during encoding or decoding.
.in-5
.sp
.I GSM_OPT_FAST
Faster compression algorithm.
.br
.in+5
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.
.br
The value passed to 
.br
.nf
	gsm_option(handle, GSM_OPT_FAST, & value)
.fi
.br 
functions as a boolean flag; if it is zero, the regular algorithm
will be used, if not, the faster version will be used.
.br
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.
.br
This option can be set any time during encoding or decoding.
.in-5
.ne 5
.sp
.PP
.I GSM_OPT_LTP_CUT
Enable, disable, or query the LTP cut-off optimization.
.br
.in+5
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.
.br
The value passed to 
.br
.nf
	gsm_option(handle, GSM_OPT_LTP_CUT, & value)
.fi
.br 
turns the optimization on if nonzero, and off if zero.
.br
This option can be set any time during encoding
or decoding; it will only affect the encoding pass, not
the decoding.
.SH "RETURN VALUE"
gsm_option() returns -1 if an option is not supported, the
previous value of the option otherwise.
.SH BUGS
Please direct bug reports to [e-mail] and [e-mail].
.SH "SEE ALSO"
toast(1), gsm(3), gsm_explode(3), gsm_print(3)