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CentOS 2.1AS(Slurm) |
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gsm(3) |
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gsm_create, gsm_destroy, gsm_encode, gsm_decode — GSM 06.10 lossy sound compression
#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;
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.
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.
#include "gsm.h"
gsm handle;
gsm_frame buf;
gsm_signal sample[160];
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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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); |
}
Please direct bug reports to jutta@cs.tu-berlin.de and cabo@cs.tu-berlin.de.
toast(1), gsm_print(3), gsm_explode(3), gsm_option(3)
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gsm(3) | |