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106 lines
2.7 KiB
106 lines
2.7 KiB
.\"
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.\" Copyright 1992 by Jutta Degener and Carsten Bormann, Technische
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.\" Universitaet Berlin. See the accompanying file "COPYRIGHT" for
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.\" details. THERE IS ABSOLUTELY NO WARRANTY FOR THIS SOFTWARE.
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.\"
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.PU
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.TH GSM 3
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.SH NAME
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gsm_create, gsm_destroy, gsm_encode, gsm_decode \(em GSM\ 06.10 lossy sound compression
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.SH SYNOPSIS
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.PP
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#include "gsm.h"
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.PP
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gsm gsm_create();
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.PP
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void gsm_encode(handle, src, dst)
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.br
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gsm handle;
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.br
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gsm_signal src[160];
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.br
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gsm_frame dst;
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.PP
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int gsm_decode(handle, src, dst)
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.br
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gsm handle;
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.br
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gsm_frame src;
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.br
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gsm_signal dst[160];
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.PP
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void gsm_destroy(handle)
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.br
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gsm handle;
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.br
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.SH "DESCRIPTION"
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Gsm is an implementation of the final draft GSM 06.10
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standard for full-rate speech transcoding.
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.PP
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gsm_create() initializes a gsm pass and returns a 'gsm' object
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which can be used as a handle in subsequent calls to gsm_decode(),
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gsm_encode() or gsm_destroy().
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.PP
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gsm_encode() encodes an array of 160 13-bit samples (given as
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gsm_signal's, signed integral values of at least 16 bits) into
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a gsm_frame of 33 bytes.
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(gsm_frame is a type defined as an array of 33 gsm_bytes in gsm.h.)
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.PP
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gsm_decode() decodes a gsm_frame into an array of 160 13-bit samples
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(given as gsm_signals), which sound rather like what you handed to
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gsm_encode() on the other side of the wire.
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.PP
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gsm_destroy() finishes a gsm pass and frees all storage associated
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with it.
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.SS "Sample format"
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The following scaling is assumed for input to the algorithm:
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.br
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.nf
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0 1 11 12
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S..v..v..v..v..v..v..v..v..v..v..v..v..*..*..*
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.nf
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.br
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Only the top 13 bits are used as a signed input value.
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The output of gsm_decode() has the three lower bits set to zero.
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.\" .SH OPTIONS
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.SH "RETURN VALUE"
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gsm_create() returns an opaque handle object of type gsm, or 0 on error.
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gsm_decode() returns -1 if the passed frame is invalid, else 0.
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.SH EXAMPLE
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.nf
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#include "gsm.h"
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gsm handle;
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gsm_frame buf;
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gsm_signal sample[160];
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int cc, soundfd;
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play() { /* read compressed data from standard input, write to soundfd */
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if (!(handle = gsm_create())) error...
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while (cc = read(0, (char *)buf, sizeof buf)) {
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if (cc != sizeof buf) error...
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if (gsm_decode(handle, buf, sample) < 0) error...
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if (write(soundfd, sample, sizeof sample) != sizeof sample)
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error...
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}
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gsm_destroy(handle);
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}
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record() { /* read from soundfd, write compressed to standard output */
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if (!(handle = gsm_create())) error...
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while (cc = read(soundfd, sample, sizeof sample)) {
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if (cc != sizeof sample) error...
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gsm_encode(handle, sample, buf);
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if (write(1, (char *)buf, sizeof buf) != sizeof sample)
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error...
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}
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gsm_destroy(handle);
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}
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.nf
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.SH BUGS
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Please direct bug reports to jutta@pobox.com and cabo@tzi.org.
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.SH "SEE ALSO"
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toast(1), gsm_print(3), gsm_explode(3), gsm_option(3)
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