106 lines
2.8 KiB
Groff
106 lines
2.8 KiB
Groff
|
.\"
|
||
|
|
.\" Copyright 1992 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 3
|
||
|
|
.SH NAME
|
||
|
|
gsm_create, gsm_destroy, gsm_encode, gsm_decode \(em GSM\ 06.10 lossy sound compression
|
||
|
|
.SH SYNOPSIS
|
||
|
|
.PP
|
||
|
|
#include "gsm.h"
|
||
|
|
.PP
|
||
|
|
gsm gsm_create();
|
||
|
|
.PP
|
||
|
|
void gsm_encode(handle, src, dst)
|
||
|
|
.br
|
||
|
|
gsm handle;
|
||
|
|
.br
|
||
|
|
gsm_signal src[160];
|
||
|
|
.br
|
||
|
|
gsm_frame dst;
|
||
|
|
.PP
|
||
|
|
int gsm_decode(handle, src, dst)
|
||
|
|
.br
|
||
|
|
gsm handle;
|
||
|
|
.br
|
||
|
|
gsm_frame src;
|
||
|
|
.br
|
||
|
|
gsm_signal dst[160];
|
||
|
|
.PP
|
||
|
|
void gsm_destroy(handle)
|
||
|
|
.br
|
||
|
|
gsm handle;
|
||
|
|
.br
|
||
|
|
.SH "DESCRIPTION"
|
||
|
|
Gsm is an implementation of the final draft GSM 06.10
|
||
|
|
standard for full-rate speech transcoding.
|
||
|
|
.PP
|
||
|
|
gsm_create() initializes a gsm pass and returns a 'gsm' object
|
||
|
|
which can be used as a handle in subsequent calls to gsm_decode(),
|
||
|
|
gsm_encode() or gsm_destroy().
|
||
|
|
.PP
|
||
|
|
gsm_encode() encodes an array of 160 13-bit samples (given as
|
||
|
|
gsm_signal's, signed integral values of at least 16 bits) into
|
||
|
|
a gsm_frame of 33 bytes.
|
||
|
|
(gsm_frame is a type defined as an array of 33 gsm_bytes in gsm.h.)
|
||
|
|
.PP
|
||
|
|
gsm_decode() decodes a gsm_frame into an array of 160 13-bit samples
|
||
|
|
(given as gsm_signals), which sound rather like what you handed to
|
||
|
|
gsm_encode() on the other side of the wire.
|
||
|
|
.PP
|
||
|
|
gsm_destroy() finishes a gsm pass and frees all storage associated
|
||
|
|
with it.
|
||
|
|
.SS "Sample format"
|
||
|
|
The following scaling is assumed for input to the algorithm:
|
||
|
|
.br
|
||
|
|
.nf
|
||
|
|
0 1 11 12
|
||
|
|
S..v..v..v..v..v..v..v..v..v..v..v..v..*..*..*
|
||
|
|
.nf
|
||
|
|
.br
|
||
|
|
Only the top 13 bits are used as a signed input value.
|
||
|
|
The output of gsm_decode() has the three lower bits set to zero.
|
||
|
|
.\" .SH OPTIONS
|
||
|
|
.SH "RETURN VALUE"
|
||
|
|
gsm_create() returns an opaque handle object of type gsm, or 0 on error.
|
||
|
|
gsm_decode() returns -1 if the passed frame is invalid, else 0.
|
||
|
|
.SH EXAMPLE
|
||
|
|
.nf
|
||
|
|
#include "gsm.h"
|
||
|
|
|
||
|
|
gsm handle;
|
||
|
|
gsm_frame buf;
|
||
|
|
gsm_signal sample[160];
|
||
|
|
int cc, soundfd;
|
||
|
|
|
||
|
|
play() { /* read compressed data from standard input, write to soundfd */
|
||
|
|
|
||
|
|
if (!(handle = gsm_create())) error...
|
||
|
|
while (cc = read(0, (char *)buf, sizeof buf)) {
|
||
|
|
if (cc != sizeof buf) error...
|
||
|
|
if (gsm_decode(handle, buf, sample) < 0) error...
|
||
|
|
if (write(soundfd, sample, sizeof sample) != sizeof sample)
|
||
|
|
error...
|
||
|
|
}
|
||
|
|
gsm_destroy(handle);
|
||
|
|
}
|
||
|
|
|
||
|
|
record() { /* read from soundfd, write compressed to standard output */
|
||
|
|
|
||
|
|
if (!(handle = gsm_create())) error...
|
||
|
|
while (cc = read(soundfd, sample, sizeof sample)) {
|
||
|
|
if (cc != sizeof sample) error...
|
||
|
|
gsm_encode(handle, sample, buf);
|
||
|
|
if (write(1, (char *)buf, sizeof buf) != sizeof sample)
|
||
|
|
error...
|
||
|
|
}
|
||
|
|
gsm_destroy(handle);
|
||
|
|
}
|
||
|
|
.nf
|
||
|
|
.SH BUGS
|
||
|
|
Please direct bug reports to jutta@cs.tu-berlin.de and cabo@cs.tu-berlin.de.
|
||
|
|
.SH "SEE ALSO"
|
||
|
|
toast(1), gsm_print(3), gsm_explode(3), gsm_option(3)
|