Wed Oct 28 11:51:03 2009

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: 153710 $")
00029 
00030 #include "asterisk/mod_format.h"
00031 #include "asterisk/module.h"
00032 #include "asterisk/endian.h"
00033 
00034 #include "msgsm.h"
00035 
00036 /* Some Ideas for this code came from makegsme.c by Jeffrey Chilton */
00037 
00038 /* Portions of the conversion code are by guido@sienanet.it */
00039 
00040 #define  GSM_FRAME_SIZE 33
00041 #define  GSM_SAMPLES 160
00042 
00043 /* silent gsm frame */
00044 /* begin binary data: */
00045 char gsm_silence[] = /* 33 */
00046 {0xD8,0x20,0xA2,0xE1,0x5A,0x50,0x00,0x49,0x24,0x92,0x49,0x24,0x50,0x00,0x49
00047 ,0x24,0x92,0x49,0x24,0x50,0x00,0x49,0x24,0x92,0x49,0x24,0x50,0x00,0x49,0x24
00048 ,0x92,0x49,0x24};
00049 /* end binary data. size = 33 bytes */
00050 
00051 static struct ast_frame *gsm_read(struct ast_filestream *s, int *whennext)
00052 {
00053    int res;
00054 
00055    s->fr.frametype = AST_FRAME_VOICE;
00056    s->fr.subclass = AST_FORMAT_GSM;
00057    AST_FRAME_SET_BUFFER(&(s->fr), s->buf, AST_FRIENDLY_OFFSET, GSM_FRAME_SIZE)
00058    s->fr.mallocd = 0;
00059    if ((res = fread(s->fr.data.ptr, 1, GSM_FRAME_SIZE, s->f)) != GSM_FRAME_SIZE) {
00060       if (res)
00061          ast_log(LOG_WARNING, "Short read (%d) (%s)!\n", res, strerror(errno));
00062       return NULL;
00063    }
00064    *whennext = s->fr.samples = GSM_SAMPLES;
00065    return &s->fr;
00066 }
00067 
00068 static int gsm_write(struct ast_filestream *fs, struct ast_frame *f)
00069 {
00070    int res;
00071    unsigned char gsm[2*GSM_FRAME_SIZE];
00072 
00073    if (f->frametype != AST_FRAME_VOICE) {
00074       ast_log(LOG_WARNING, "Asked to write non-voice frame!\n");
00075       return -1;
00076    }
00077    if (f->subclass != AST_FORMAT_GSM) {
00078       ast_log(LOG_WARNING, "Asked to write non-GSM frame (%d)!\n", f->subclass);
00079       return -1;
00080    }
00081    if (!(f->datalen % 65)) {
00082       /* This is in MSGSM format, need to be converted */
00083       int len=0;
00084       while(len < f->datalen) {
00085          conv65(f->data.ptr + len, gsm);
00086          if ((res = fwrite(gsm, 1, 2*GSM_FRAME_SIZE, fs->f)) != 2*GSM_FRAME_SIZE) {
00087             ast_log(LOG_WARNING, "Bad write (%d/66): %s\n", res, strerror(errno));
00088             return -1;
00089          }
00090          len += 65;
00091       }
00092    } else {
00093       if (f->datalen % GSM_FRAME_SIZE) {
00094          ast_log(LOG_WARNING, "Invalid data length, %d, should be multiple of 33\n", f->datalen);
00095          return -1;
00096       }
00097       if ((res = fwrite(f->data.ptr, 1, f->datalen, fs->f)) != f->datalen) {
00098             ast_log(LOG_WARNING, "Bad write (%d/33): %s\n", res, strerror(errno));
00099             return -1;
00100       }
00101    }
00102    return 0;
00103 }
00104 
00105 static int gsm_seek(struct ast_filestream *fs, off_t sample_offset, int whence)
00106 {
00107    off_t offset=0,min,cur,max,distance;
00108    
00109    min = 0;
00110    cur = ftello(fs->f);
00111    fseeko(fs->f, 0, SEEK_END);
00112    max = ftello(fs->f);
00113    /* have to fudge to frame here, so not fully to sample */
00114    distance = (sample_offset/GSM_SAMPLES) * GSM_FRAME_SIZE;
00115    if(whence == SEEK_SET)
00116       offset = distance;
00117    else if(whence == SEEK_CUR || whence == SEEK_FORCECUR)
00118       offset = distance + cur;
00119    else if(whence == SEEK_END)
00120       offset = max - distance;
00121    /* Always protect against seeking past the begining. */
00122    offset = (offset < min)?min:offset;
00123    if (whence != SEEK_FORCECUR) {
00124       offset = (offset > max)?max:offset;
00125    } else if (offset > max) {
00126       int i;
00127       fseeko(fs->f, 0, SEEK_END);
00128       for (i=0; i< (offset - max) / GSM_FRAME_SIZE; i++) {
00129          if (!fwrite(gsm_silence, 1, GSM_FRAME_SIZE, fs->f)) {
00130             ast_log(LOG_WARNING, "fwrite() failed: %s\n", strerror(errno));
00131          }
00132       }
00133    }
00134    return fseeko(fs->f, offset, SEEK_SET);
00135 }
00136 
00137 static int gsm_trunc(struct ast_filestream *fs)
00138 {
00139    return ftruncate(fileno(fs->f), ftello(fs->f));
00140 }
00141 
00142 static off_t gsm_tell(struct ast_filestream *fs)
00143 {
00144    off_t offset = ftello(fs->f);
00145    return (offset/GSM_FRAME_SIZE)*GSM_SAMPLES;
00146 }
00147 
00148 static const struct ast_format gsm_f = {
00149    .name = "gsm",
00150    .exts = "gsm",
00151    .format = AST_FORMAT_GSM,
00152    .write = gsm_write,
00153    .seek =  gsm_seek,
00154    .trunc = gsm_trunc,
00155    .tell =  gsm_tell,
00156    .read =  gsm_read,
00157    .buf_size = 2*GSM_FRAME_SIZE + AST_FRIENDLY_OFFSET,   /* 2 gsm frames */
00158 };
00159 
00160 static int load_module(void)
00161 {
00162    if (ast_format_register(&gsm_f))
00163       return AST_MODULE_LOAD_FAILURE;
00164    return AST_MODULE_LOAD_SUCCESS;
00165 }
00166 
00167 static int unload_module(void)
00168 {
00169    return ast_format_unregister(gsm_f.name);
00170 }  
00171 
00172 AST_MODULE_INFO_STANDARD(ASTERISK_GPL_KEY, "Raw GSM data");

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