GSM(3)							     Library Functions Manual							    GSM(3)

gsm_create, gsm_destroy, gsm_encode, gsm_decode -- GSM 06.10 lossy sound compression SYNOPSIS
#include "gsm.h" gsm gsm_create(); void gsm_encode(handle, src, dst) gsm handle; gsm_signal src[160]; gsm_frame dst; int gsm_decode(handle, src, dst) gsm handle; gsm_frame src; gsm_signal dst[160]; void gsm_destroy(handle) gsm handle; DESCRIPTION
Gsm is an implementation of the final draft GSM 06.10 standard for full-rate speech transcoding. 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(). 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.) 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. gsm_destroy() finishes a gsm pass and frees all storage associated with it. Sample format The following scaling is assumed for input to the algorithm: 0 1 11 12 S..v..v..v..v..v..v..v..v..v..v..v..v..*..*..* 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. 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. EXAMPLE
#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); } BUGS
Please direct bug reports to and SEE ALSO
toast(1), gsm_print(3), gsm_explode(3), gsm_option(3) GSM(3)