Sat Aug 6 00:39:28 2011

Asterisk developer's documentation


format_gsm.c

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00001 /*
00002  * Asterisk -- An open source telephony toolkit.
00003  *
00004  * Copyright (C) 1999 - 2005, Digium, Inc.
00005  *
00006  * Mark Spencer <markster@digium.com>
00007  *
00008  * See http://www.asterisk.org for more information about
00009  * the Asterisk project. Please do not directly contact
00010  * any of the maintainers of this project for assistance;
00011  * the project provides a web site, mailing lists and IRC
00012  * channels for your use.
00013  *
00014  * This program is free software, distributed under the terms of
00015  * the GNU General Public License Version 2. See the LICENSE file
00016  * at the top of the source tree.
00017  */
00018 
00019 /*! \file
00020  *
00021  * \brief Save to raw, headerless GSM data.
00022  * \arg File name extension: gsm
00023  * \ingroup formats
00024  */
00025  
00026 #include "asterisk.h"
00027 
00028 ASTERISK_FILE_VERSION(__FILE__, "$Revision: 233782 $")
00029 
00030 #include <unistd.h>
00031 #include <netinet/in.h>
00032 #include <arpa/inet.h>
00033 #include <stdlib.h>
00034 #include <sys/time.h>
00035 #include <stdio.h>
00036 #include <errno.h>
00037 #include <string.h>
00038 
00039 #include "asterisk/lock.h"
00040 #include "asterisk/channel.h"
00041 #include "asterisk/file.h"
00042 #include "asterisk/logger.h"
00043 #include "asterisk/sched.h"
00044 #include "asterisk/module.h"
00045 #include "asterisk/endian.h"
00046 
00047 #include "msgsm.h"
00048 
00049 /* Some Ideas for this code came from makegsme.c by Jeffrey Chilton */
00050 
00051 /* Portions of the conversion code are by guido@sienanet.it */
00052 
00053 #define  GSM_FRAME_SIZE 33
00054 #define  GSM_SAMPLES 160
00055 
00056 /* silent gsm frame */
00057 /* begin binary data: */
00058 char gsm_silence[] = /* 33 */
00059 {0xD8,0x20,0xA2,0xE1,0x5A,0x50,0x00,0x49,0x24,0x92,0x49,0x24,0x50,0x00,0x49
00060 ,0x24,0x92,0x49,0x24,0x50,0x00,0x49,0x24,0x92,0x49,0x24,0x50,0x00,0x49,0x24
00061 ,0x92,0x49,0x24};
00062 /* end binary data. size = 33 bytes */
00063 
00064 static struct ast_frame *gsm_read(struct ast_filestream *s, int *whennext)
00065 {
00066    int res;
00067 
00068    s->fr.frametype = AST_FRAME_VOICE;
00069    s->fr.subclass = AST_FORMAT_GSM;
00070    AST_FRAME_SET_BUFFER(&(s->fr), s->buf, AST_FRIENDLY_OFFSET, GSM_FRAME_SIZE)
00071    s->fr.mallocd = 0;
00072    if ((res = fread(s->fr.data, 1, GSM_FRAME_SIZE, s->f)) != GSM_FRAME_SIZE) {
00073       if (res)
00074          ast_log(LOG_WARNING, "Short read (%d) (%s)!\n", res, strerror(errno));
00075       return NULL;
00076    }
00077    *whennext = s->fr.samples = GSM_SAMPLES;
00078    return &s->fr;
00079 }
00080 
00081 static int gsm_write(struct ast_filestream *fs, struct ast_frame *f)
00082 {
00083    int res;
00084    unsigned char gsm[2*GSM_FRAME_SIZE];
00085 
00086    if (f->frametype != AST_FRAME_VOICE) {
00087       ast_log(LOG_WARNING, "Asked to write non-voice frame!\n");
00088       return -1;
00089    }
00090    if (f->subclass != AST_FORMAT_GSM) {
00091       ast_log(LOG_WARNING, "Asked to write non-GSM frame (%d)!\n", f->subclass);
00092       return -1;
00093    }
00094    if (!(f->datalen % 65)) {
00095       /* This is in MSGSM format, need to be converted */
00096       int len=0;
00097       while(len < f->datalen) {
00098          conv65(f->data + len, gsm);
00099          if ((res = fwrite(gsm, 1, 2*GSM_FRAME_SIZE, fs->f)) != 2*GSM_FRAME_SIZE) {
00100             ast_log(LOG_WARNING, "Bad write (%d/66): %s\n", res, strerror(errno));
00101             return -1;
00102          }
00103          len += 65;
00104       }
00105    } else {
00106       if (f->datalen % GSM_FRAME_SIZE) {
00107          ast_log(LOG_WARNING, "Invalid data length, %d, should be multiple of 33\n", f->datalen);
00108          return -1;
00109       }
00110       if ((res = fwrite(f->data, 1, f->datalen, fs->f)) != f->datalen) {
00111             ast_log(LOG_WARNING, "Bad write (%d/33): %s\n", res, strerror(errno));
00112             return -1;
00113       }
00114    }
00115    return 0;
00116 }
00117 
00118 static int gsm_seek(struct ast_filestream *fs, off_t sample_offset, int whence)
00119 {
00120    off_t offset=0,min,cur,max,distance;
00121    
00122    min = 0;
00123    cur = ftello(fs->f);
00124    fseeko(fs->f, 0, SEEK_END);
00125    max = ftello(fs->f);
00126    /* have to fudge to frame here, so not fully to sample */
00127    distance = (sample_offset/GSM_SAMPLES) * GSM_FRAME_SIZE;
00128    if(whence == SEEK_SET)
00129       offset = distance;
00130    else if(whence == SEEK_CUR || whence == SEEK_FORCECUR)
00131       offset = distance + cur;
00132    else if(whence == SEEK_END)
00133       offset = max - distance;
00134    /* Always protect against seeking past the begining. */
00135    offset = (offset < min)?min:offset;
00136    if (whence != SEEK_FORCECUR) {
00137       offset = (offset > max)?max:offset;
00138    } else if (offset > max) {
00139       int i;
00140       fseeko(fs->f, 0, SEEK_END);
00141       for (i=0; i< (offset - max) / GSM_FRAME_SIZE; i++) {
00142          if (!fwrite(gsm_silence, 1, GSM_FRAME_SIZE, fs->f)) {
00143             ast_log(LOG_WARNING, "fwrite() failed: %s\n", strerror(errno));
00144          }
00145       }
00146    }
00147    return fseeko(fs->f, offset, SEEK_SET);
00148 }
00149 
00150 static int gsm_trunc(struct ast_filestream *fs)
00151 {
00152    return ftruncate(fileno(fs->f), ftello(fs->f));
00153 }
00154 
00155 static off_t gsm_tell(struct ast_filestream *fs)
00156 {
00157    off_t offset = ftello(fs->f);
00158    return (offset/GSM_FRAME_SIZE)*GSM_SAMPLES;
00159 }
00160 
00161 static const struct ast_format gsm_f = {
00162    .name = "gsm",
00163    .exts = "gsm",
00164    .format = AST_FORMAT_GSM,
00165    .write = gsm_write,
00166    .seek =  gsm_seek,
00167    .trunc = gsm_trunc,
00168    .tell =  gsm_tell,
00169    .read =  gsm_read,
00170    .buf_size = 2*GSM_FRAME_SIZE + AST_FRIENDLY_OFFSET,   /* 2 gsm frames */
00171 };
00172 
00173 static int load_module(void)
00174 {
00175    return ast_format_register(&gsm_f);
00176 }
00177 
00178 static int unload_module(void)
00179 {
00180    return ast_format_unregister(gsm_f.name);
00181 }  
00182 
00183 AST_MODULE_INFO(ASTERISK_GPL_KEY, AST_MODFLAG_LOAD_FIRST, "Raw GSM data",
00184    .load = load_module,
00185    .unload = unload_module,
00186 );

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