res_format_attr_silk.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2011, Digium, Inc.
 *
 * David Vossel <[email protected]>
 *
 * See http://www.asterisk.org for more information about
 * the Asterisk project. Please do not directly contact
 * any of the maintainers of this project for assistance;
 * the project provides a web site, mailing lists and IRC
 * channels for your use.
 *
 * This program is free software, distributed under the terms of
 * the GNU General Public License Version 2. See the LICENSE file
 * at the top of the source tree.
 */

/*!
 * \file
 * \brief SILK format attribute interface
 *
 * \author David Vossel <[email protected]>
 */

/*** MODULEINFO
 <support_level>core</support_level>
 ***/

#include "asterisk.h"

#include <ctype.h> /* for tolower */

#include "asterisk/module.h"
#include "asterisk/format.h"
#include "asterisk/logger.h" /* for ast_log, LOG_WARNING */
#include "asterisk/strings.h" /* for ast_str_append */
#include "asterisk/utils.h" /* for MAX, MIN */

/*!
 * \brief SILK attribute structure.
 *
 * \note The only attribute that affects compatibility here is the sample rate.
 */
struct silk_attr {
 unsigned int maxbitrate;
 unsigned int dtx;
 unsigned int fec;
 unsigned int packetloss_percentage;
};

static void silk_destroy(struct ast_format *format)
{
 struct silk_attr *attr = ast_format_get_attribute_data(format);

 ast_free(attr);
}

static void attr_init(struct silk_attr *attr)
{
 memset(attr, 0, sizeof(*attr));
}

static int silk_clone(const struct ast_format *src, struct ast_format *dst)
{
 struct silk_attr *original = ast_format_get_attribute_data(src);
 struct silk_attr *attr = ast_malloc(sizeof(*attr));

 if (!attr) {
 return -1;
 }

 if (original) {
 *attr = *original;
 } else {
 attr_init(attr);
 }

 ast_format_set_attribute_data(dst, attr);

 return 0;
}

static struct ast_format *silk_parse_sdp_fmtp(const struct ast_format *format, const char *attributes)
{
 char *attribs = ast_strdupa(attributes), *attrib;
 struct ast_format *cloned;
 struct silk_attr *attr;
 unsigned int val;

 cloned = ast_format_clone(format);
 if (!cloned) {
 return NULL;
 }
 attr = ast_format_get_attribute_data(cloned);

 /* lower-case everything, so we are case-insensitive */
 for (attrib = attribs; *attrib; ++attrib) {
 *attrib = tolower(*attrib);
 } /* based on channels/chan_sip.c:process_a_sdp_image() */

 if (sscanf(attribs, "maxaveragebitrate=%30u", &val) == 1) {
 attr->maxbitrate = val;
 }
 if (sscanf(attribs, "usedtx=%30u", &val) == 1) {
 attr->dtx = val;
 }
 if (sscanf(attribs, "useinbandfec=%30u", &val) == 1) {
 attr->fec = val;
 }

 return cloned;
}

static void silk_generate_sdp_fmtp(const struct ast_format *format, unsigned int payload, struct ast_str **str)
{
 struct silk_attr *attr = ast_format_get_attribute_data(format);

 if (!attr) {
 return;
 }

 if ((attr->maxbitrate > 5000) && (attr->maxbitrate < 40000)) {
 ast_str_append(str, 0, "a=fmtp:%u maxaveragebitrate=%u\r\n", payload, attr->maxbitrate);
 }

 if (attr->dtx) {
 ast_str_append(str, 0, "a=fmtp:%u usedtx=%u\r\n", payload, attr->dtx);
 }
 if (attr->fec) {
 ast_str_append(str, 0, "a=fmtp:%u useinbandfec=%u\r\n", payload, attr->fec);
 }
}

static enum ast_format_cmp_res silk_cmp(const struct ast_format *format1, const struct ast_format *format2)
{
 if (ast_format_get_sample_rate(format1) == ast_format_get_sample_rate(format2)) {
 return AST_FORMAT_CMP_EQUAL;
 }

 return AST_FORMAT_CMP_NOT_EQUAL;
}

static struct ast_format *silk_getjoint(const struct ast_format *format1, const struct ast_format *format2)
{
 struct silk_attr *attr1 = ast_format_get_attribute_data(format1);
 struct silk_attr *attr2 = ast_format_get_attribute_data(format2);
 struct ast_format *jointformat;
 struct silk_attr *attr_res;

 if (ast_format_get_sample_rate(format1) != ast_format_get_sample_rate(format2)) {
 return NULL;
 }

 jointformat = ast_format_clone(format1);
 if (!jointformat) {
 return NULL;
 }
 attr_res = ast_format_get_attribute_data(jointformat);

 if (!attr1 || !attr2) {
 attr_init(attr_res);
 } else {
 /* Take the lowest max bitrate */
 attr_res->maxbitrate = MIN(attr1->maxbitrate, attr2->maxbitrate);

 /* Only do dtx if both sides want it. DTX is a trade off between
 * computational complexity and bandwidth. */
 attr_res->dtx = attr1->dtx && attr2->dtx ? 1 : 0;

 /* Only do FEC if both sides want it. If a peer specifically requests not
 * to receive with FEC, it may be a waste of bandwidth. */
 attr_res->fec = attr1->fec && attr2->fec ? 1 : 0;

 /* Use the maximum packetloss percentage between the two attributes. This affects how
 * much redundancy is used in the FEC. */
 attr_res->packetloss_percentage = MAX(attr1->packetloss_percentage, attr2->packetloss_percentage);
 }

 return jointformat;
}

static struct ast_format *silk_set(const struct ast_format *format, const char *name, const char *value)
{
 struct ast_format *cloned;
 struct silk_attr *attr;
 unsigned int val;

 if (sscanf(value, "%30u", &val) != 1) {
 ast_log(LOG_WARNING, "Unknown value '%s' for attribute type '%s'\n",
 value, name);
 return NULL;
 }

 cloned = ast_format_clone(format);
 if (!cloned) {
 return NULL;
 }
 attr = ast_format_get_attribute_data(cloned);

 if (!strcasecmp(name, "max_bitrate")) {
 attr->maxbitrate = val;
 } else if (!strcasecmp(name, "dtx")) {
 attr->dtx = val;
 } else if (!strcasecmp(name, "fec")) {
 attr->fec = val;
 } else if (!strcasecmp(name, "packetloss_percentage")) {
 attr->packetloss_percentage = val;
 } else {
 ast_log(LOG_WARNING, "unknown attribute type %s\n", name);
 }

 return cloned;
}

static const void *silk_get(const struct ast_format *format, const char *name)
{
 struct silk_attr *attr = ast_format_get_attribute_data(format);
 unsigned int *val;

 if (!strcasecmp(name, "max_bitrate")) {
 val = &attr->maxbitrate;
 } else if (!strcasecmp(name, "dtx")) {
 val = &attr->dtx;
 } else if (!strcasecmp(name, "fec")) {
 val = &attr->fec;
 } else if (!strcasecmp(name, "packetloss_percentage")) {
 val = &attr->packetloss_percentage;
 } else {
 ast_log(LOG_WARNING, "unknown attribute type %s\n", name);
 return NULL;
 }

 return val;
}

static struct ast_format_interface silk_interface = {
 .format_destroy = silk_destroy,
 .format_clone = silk_clone,
 .format_cmp = silk_cmp,
 .format_get_joint = silk_getjoint,
 .format_attribute_set = silk_set,
 .format_attribute_get = silk_get,
 .format_parse_sdp_fmtp = silk_parse_sdp_fmtp,
 .format_generate_sdp_fmtp = silk_generate_sdp_fmtp,
};

static int load_module(void)
{
 if (ast_format_interface_register("silk", &silk_interface)) {
 return AST_MODULE_LOAD_DECLINE;
 }

 return AST_MODULE_LOAD_SUCCESS;
}

static int unload_module(void)
{
 return 0;
}

AST_MODULE_INFO(ASTERISK_GPL_KEY, AST_MODFLAG_LOAD_ORDER, "SILK Format Attribute Module",
 .support_level = AST_MODULE_SUPPORT_CORE,
 .load = load_module,
 .unload = unload_module,
 .load_pri = AST_MODPRI_CHANNEL_DEPEND,
);