/*
  * copyright (c) 2007 Luca Abeni
  *
  * This file is part of FFmpeg.
  *
  * FFmpeg is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  *
  * FFmpeg is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with FFmpeg; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 

 #include <string.h>

 #include "libavutil/avstring.h"
 #include "libavutil/base64.h"

 #include "libavutil/dict.h"

 #include "libavutil/parseutils.h"

 #include "libavutil/opt.h"

 #include "libavcodec/xiph.h"

 #include "libavcodec/mpeg4audio.h"

 #include "avformat.h"

 #include "internal.h"

 #include "avc.h"

 #include "hevc.h"

 #include "rtp.h"

 #if CONFIG_NETWORK
 #include "network.h"
 #endif

 #if CONFIG_RTP_MUXER

 #define MAX_EXTRADATA_SIZE ((INT_MAX - 10) / 2)
 
 struct sdp_session_level {
     int sdp_version;      /**< protocol version (currently 0) */

     int id;               /**< session ID */

     int version;          /**< session version */
     int start_time;       /**< session start time (NTP time, in seconds),

                                or 0 in case of permanent session */

     int end_time;         /**< session end time (NTP time, in seconds),
                                or 0 if the session is not bounded */
     int ttl;              /**< TTL, in case of multicast stream */
     const char *user;     /**< username of the session's creator */
     const char *src_addr; /**< IP address of the machine from which the session was created */

     const char *src_type; /**< address type of src_addr */

     const char *dst_addr; /**< destination IP address (can be multicast) */

     const char *dst_type; /**< destination IP address type */

     const char *name;     /**< session name (can be an empty string) */
 };
 

 static void sdp_write_address(char *buff, int size, const char *dest_addr,
                               const char *dest_type, int ttl)

 {
     if (dest_addr) {

         if (!dest_type)
             dest_type = "IP4";

         if (ttl > 0 && !strcmp(dest_type, "IP4")) {
             /* The TTL should only be specified for IPv4 multicast addresses,
              * not for IPv6. */

             av_strlcatf(buff, size, "c=IN %s %s/%d\r\n", dest_type, dest_addr, ttl);

         } else {

             av_strlcatf(buff, size, "c=IN %s %s\r\n", dest_type, dest_addr);

         }
     }
 }
 
 static void sdp_write_header(char *buff, int size, struct sdp_session_level *s)
 {
     av_strlcatf(buff, size, "v=%d\r\n"

                             "o=- %d %d IN %s %s\r\n"

                             "s=%s\r\n",

                             s->sdp_version,

                             s->id, s->version, s->src_type, s->src_addr,

                             s->name);

     sdp_write_address(buff, size, s->dst_addr, s->dst_type, s->ttl);

     av_strlcatf(buff, size, "t=%d %d\r\n"
                             "a=tool:libavformat " AV_STRINGIFY(LIBAVFORMAT_VERSION) "\r\n",
                             s->start_time, s->end_time);

 }
 

 #if CONFIG_NETWORK

 static int resolve_destination(char *dest_addr, int size, char *type,

                                int type_size)

 {

     struct addrinfo hints = { 0 }, *ai;

     int is_multicast;

     av_strlcpy(type, "IP4", type_size);

     if (!dest_addr[0])

         return 0;

 
     /* Resolve the destination, since it must be written
      * as a numeric IP address in the SDP. */
 
     if (getaddrinfo(dest_addr, NULL, &hints, &ai))

         return 0;

     getnameinfo(ai->ai_addr, ai->ai_addrlen, dest_addr, size,
                 NULL, 0, NI_NUMERICHOST);

 #ifdef AF_INET6

     if (ai->ai_family == AF_INET6)
         av_strlcpy(type, "IP6", type_size);

 #endif

     is_multicast = ff_is_multicast_address(ai->ai_addr);

     freeaddrinfo(ai);

     return is_multicast;

 }
 #else

 static int resolve_destination(char *dest_addr, int size, char *type,

                                int type_size)

 {

     return 0;

 }
 #endif
 

 static int sdp_get_address(char *dest_addr, int size, int *ttl, const char *url)

 {
     int port;
     const char *p;

     char proto[32];

     av_url_split(proto, sizeof(proto), NULL, 0, dest_addr, size, &port, NULL, 0, url);

 
     *ttl = 0;

     if (strcmp(proto, "rtp") && strcmp(proto, "srtp")) {

         /* The url isn't for the actual rtp sessions,
          * don't parse out anything else than the destination.
          */
         return 0;
     }
 

     p = strchr(url, '?');
     if (p) {
         char buff[64];
 

         if (av_find_info_tag(buff, sizeof(buff), "ttl", p)) {

             *ttl = strtol(buff, NULL, 10);
         } else {
             *ttl = 5;
         }

     }
 
     return port;
 }
 

 #define MAX_PSET_SIZE 1024
 static char *extradata2psets(AVCodecContext *c)
 {
     char *psets, *p;

     const uint8_t *r;

     static const char pset_string[] = "; sprop-parameter-sets=";
     static const char profile_string[] = "; profile-level-id=";

     uint8_t *extradata = c->extradata;
     int extradata_size = c->extradata_size;
     uint8_t *tmpbuf = NULL;

     const uint8_t *sps = NULL, *sps_end;

 
     if (c->extradata_size > MAX_EXTRADATA_SIZE) {

         av_log(c, AV_LOG_ERROR, "Too much extradata!\n");

 
         return NULL;
     }

     if (c->extradata[0] == 1) {

         if (ff_avc_write_annexb_extradata(c->extradata, &extradata,
                                           &extradata_size))

             return NULL;

         tmpbuf = extradata;

     }

 
     psets = av_mallocz(MAX_PSET_SIZE);

     if (!psets) {

         av_log(c, AV_LOG_ERROR, "Cannot allocate memory for the parameter sets.\n");

         av_free(tmpbuf);

         return NULL;
     }
     memcpy(psets, pset_string, strlen(pset_string));
     p = psets + strlen(pset_string);

     r = ff_avc_find_startcode(extradata, extradata + extradata_size);
     while (r < extradata + extradata_size) {

         const uint8_t *r1;

         uint8_t nal_type;

 
         while (!*(r++));

         nal_type = *r & 0x1f;

         r1 = ff_avc_find_startcode(r, extradata + extradata_size);

         if (nal_type != 7 && nal_type != 8) { /* Only output SPS and PPS */
             r = r1;
             continue;
         }

         if (p != (psets + strlen(pset_string))) {
             *p = ',';
             p++;
         }

         if (!sps) {
             sps = r;
             sps_end = r1;
         }

         if (!av_base64_encode(p, MAX_PSET_SIZE - (p - psets), r, r1 - r)) {

             av_log(c, AV_LOG_ERROR, "Cannot Base64-encode %"PTRDIFF_SPECIFIER" %"PTRDIFF_SPECIFIER"!\n", MAX_PSET_SIZE - (p - psets), r1 - r);

             av_free(psets);

             av_free(tmpbuf);

 
             return NULL;
         }
         p += strlen(p);
         r = r1;
     }

     if (sps && sps_end - sps >= 4) {
         memcpy(p, profile_string, strlen(profile_string));
         p += strlen(p);
         ff_data_to_hex(p, sps + 1, 3, 0);
         p[6] = '\0';
     }

     av_free(tmpbuf);

 
     return psets;
 }
 

 static char *extradata2psets_hevc(AVCodecContext *c)
 {
     char *psets;
     uint8_t *extradata = c->extradata;
     int extradata_size = c->extradata_size;
     uint8_t *tmpbuf = NULL;
     int ps_pos[3] = { 0 };
     static const char * const ps_names[3] = { "vps", "sps", "pps" };
     int num_arrays, num_nalus;
     int pos, i, j;
 
     // Convert to hvcc format. Since we need to group multiple NALUs of
     // the same type, and we might need to convert from one format to the
     // other anyway, we get away with a little less work by using the hvcc
     // format.
     if (c->extradata[0] != 1) {
         AVIOContext *pb;
         if (avio_open_dyn_buf(&pb) < 0)
             return NULL;
         if (ff_isom_write_hvcc(pb, c->extradata, c->extradata_size, 0) < 0) {
             avio_close_dyn_buf(pb, &tmpbuf);
             goto err;
         }
         extradata_size = avio_close_dyn_buf(pb, &extradata);
         tmpbuf = extradata;
     }
 
     if (extradata_size < 23)
         goto err;
 
     num_arrays = extradata[22];
     pos = 23;
     for (i = 0; i < num_arrays; i++) {
         int num_nalus, nalu_type;
         if (pos + 3 > extradata_size)
             goto err;
         nalu_type = extradata[pos] & 0x3f;
         // Not including libavcodec/hevc.h to avoid confusion between
         // NAL_* with the same name for both H264 and HEVC.
         if (nalu_type == 32) // VPS
             ps_pos[0] = pos;
         else if (nalu_type == 33) // SPS
             ps_pos[1] = pos;
         else if (nalu_type == 34) // PPS
             ps_pos[2] = pos;
         num_nalus = AV_RB16(&extradata[pos + 1]);
         pos += 3;
         for (j = 0; j < num_nalus; j++) {
             int len;
             if (pos + 2 > extradata_size)
                 goto err;
             len = AV_RB16(&extradata[pos]);
             pos += 2;
             if (pos + len > extradata_size)
                 goto err;
             pos += len;
         }
     }
     if (!ps_pos[0] || !ps_pos[1] || !ps_pos[2])
         goto err;
 
     psets = av_mallocz(MAX_PSET_SIZE);
     if (!psets)
         goto err;
     psets[0] = '\0';
 
     for (i = 0; i < 3; i++) {
         pos = ps_pos[i];
 
         if (i > 0)
             av_strlcat(psets, "; ", MAX_PSET_SIZE);
         av_strlcatf(psets, MAX_PSET_SIZE, "sprop-%s=", ps_names[i]);
 
         // Skipping boundary checks in the input here; we've already traversed
         // the whole hvcc structure above without issues
         num_nalus = AV_RB16(&extradata[pos + 1]);
         pos += 3;
         for (j = 0; j < num_nalus; j++) {
             int len = AV_RB16(&extradata[pos]);
             int strpos;
             pos += 2;
             if (j > 0)
                 av_strlcat(psets, ",", MAX_PSET_SIZE);
             strpos = strlen(psets);
             if (!av_base64_encode(psets + strpos, MAX_PSET_SIZE - strpos,
                                   &extradata[pos], len)) {
                 av_free(psets);
                 goto err;
             }
             pos += len;
         }
     }
     av_free(tmpbuf);
 
     return psets;
 
 err:
     av_free(tmpbuf);
     return NULL;
 }
 

 static char *extradata2config(AVCodecContext *c)

 {
     char *config;
 

     if (c->extradata_size > MAX_EXTRADATA_SIZE) {

         av_log(c, AV_LOG_ERROR, "Too much extradata!\n");

 
         return NULL;
     }

     config = av_malloc(10 + c->extradata_size * 2);

     if (!config) {

         av_log(c, AV_LOG_ERROR, "Cannot allocate memory for the config info.\n");

         return NULL;
     }
     memcpy(config, "; config=", 9);

     ff_data_to_hex(config + 9, c->extradata, c->extradata_size, 0);

     config[9 + c->extradata_size * 2] = 0;

 
     return config;
 }
 

 static char *xiph_extradata2config(AVCodecContext *c)
 {
     char *config, *encoded_config;

     const uint8_t *header_start[3];

     int headers_len, header_len[3], config_len;
     int first_header_size;
 
     switch (c->codec_id) {

     case AV_CODEC_ID_THEORA:

         first_header_size = 42;
         break;

     case AV_CODEC_ID_VORBIS:

         first_header_size = 30;
         break;
     default:
         av_log(c, AV_LOG_ERROR, "Unsupported Xiph codec ID\n");
         return NULL;
     }
 

     if (avpriv_split_xiph_headers(c->extradata, c->extradata_size,

                               first_header_size, header_start,
                               header_len) < 0) {
         av_log(c, AV_LOG_ERROR, "Extradata corrupt.\n");
         return NULL;
     }
 
     headers_len = header_len[0] + header_len[2];
     config_len = 4 +          // count
                  3 +          // ident
                  2 +          // packet size
                  1 +          // header count
                  2 +          // header size
                  headers_len; // and the rest
 
     config = av_malloc(config_len);
     if (!config)
         goto xiph_fail;
 
     encoded_config = av_malloc(AV_BASE64_SIZE(config_len));
     if (!encoded_config) {
         av_free(config);
         goto xiph_fail;
     }
 
     config[0] = config[1] = config[2] = 0;
     config[3] = 1;

     config[4] = (RTP_XIPH_IDENT >> 16) & 0xff;
     config[5] = (RTP_XIPH_IDENT >>  8) & 0xff;
     config[6] = (RTP_XIPH_IDENT      ) & 0xff;

     config[7] = (headers_len >> 8) & 0xff;
     config[8] = headers_len & 0xff;
     config[9] = 2;
     config[10] = header_len[0];
     config[11] = 0; // size of comment header; nonexistent
     memcpy(config + 12, header_start[0], header_len[0]);
     memcpy(config + 12 + header_len[0], header_start[2], header_len[2]);
 
     av_base64_encode(encoded_config, AV_BASE64_SIZE(config_len),
                      config, config_len);
     av_free(config);
 
     return encoded_config;
 
 xiph_fail:
     av_log(c, AV_LOG_ERROR,
            "Not enough memory for configuration string\n");
     return NULL;
 }
 

 static int latm_context2profilelevel(AVCodecContext *c)
 {

     /* MP4A-LATM
      * The RTP payload format specification is described in RFC 3016
      * The encoding specifications are provided in ISO/IEC 14496-3 */
 
     int profile_level = 0x2B;
 
     /* TODO: AAC Profile only supports AAC LC Object Type.
      * Different Object Types should implement different Profile Levels */
 
     if (c->sample_rate <= 24000) {
         if (c->channels <= 2)
             profile_level = 0x28; // AAC Profile, Level 1
     } else if (c->sample_rate <= 48000) {
         if (c->channels <= 2) {
             profile_level = 0x29; // AAC Profile, Level 2
         } else if (c->channels <= 5) {
             profile_level = 0x2A; // AAC Profile, Level 4
         }
     } else if (c->sample_rate <= 96000) {
         if (c->channels <= 5) {
             profile_level = 0x2B; // AAC Profile, Level 5
         }
     }
 
     return profile_level;
 }
 

 static char *latm_context2config(AVCodecContext *c)
 {

     /* MP4A-LATM
      * The RTP payload format specification is described in RFC 3016
      * The encoding specifications are provided in ISO/IEC 14496-3 */
 
     uint8_t config_byte[6];
     int rate_index;
     char *config;
 
     for (rate_index = 0; rate_index < 16; rate_index++)

         if (avpriv_mpeg4audio_sample_rates[rate_index] == c->sample_rate)

             break;
     if (rate_index == 16) {
         av_log(c, AV_LOG_ERROR, "Unsupported sample rate\n");
         return NULL;
     }
 
     config_byte[0] = 0x40;
     config_byte[1] = 0;
     config_byte[2] = 0x20 | rate_index;
     config_byte[3] = c->channels << 4;
     config_byte[4] = 0x3f;
     config_byte[5] = 0xc0;
 
     config = av_malloc(6*2+1);
     if (!config) {
         av_log(c, AV_LOG_ERROR, "Cannot allocate memory for the config info.\n");
         return NULL;
     }
     ff_data_to_hex(config, config_byte, 6, 1);
     config[12] = 0;
 
     return config;
 }
 

 static char *sdp_write_media_attributes(char *buff, int size, AVCodecContext *c, int payload_type, AVFormatContext *fmt)

 {
     char *config = NULL;
 
     switch (c->codec_id) {

         case AV_CODEC_ID_H264: {

             int mode = 1;

             if (fmt && fmt->oformat && fmt->oformat->priv_class &&

                 av_opt_flag_is_set(fmt->priv_data, "rtpflags", "h264_mode0"))
                 mode = 0;

             if (c->extradata_size) {
                 config = extradata2psets(c);
             }

             av_strlcatf(buff, size, "a=rtpmap:%d H264/90000\r\n"

                                     "a=fmtp:%d packetization-mode=%d%s\r\n",

                                      payload_type,

                                      payload_type, mode, config ? config : "");

             break;

         }

         case AV_CODEC_ID_H261:
         {
             const char *pic_fmt = NULL;
             /* only QCIF and CIF are specified as supported in RFC 4587 */
             if (c->width == 176 && c->height == 144)
                 pic_fmt = "QCIF=1";

             else if (c->width == 352 && c->height == 288)

                 pic_fmt = "CIF=1";

             if (payload_type >= RTP_PT_PRIVATE)
                 av_strlcatf(buff, size, "a=rtpmap:%d H261/90000\r\n", payload_type);

             if (pic_fmt)
                 av_strlcatf(buff, size, "a=fmtp:%d %s\r\n", payload_type, pic_fmt);
             break;
         }

         case AV_CODEC_ID_H263:
         case AV_CODEC_ID_H263P:

             /* a=framesize is required by 3GPP TS 26.234 (PSS). It
              * actually specifies the maximum video size, but we only know
              * the current size. This is required for playback on Android
              * stagefright and on Samsung bada. */

             if (!fmt || !fmt->oformat->priv_class ||
                 !av_opt_flag_is_set(fmt->priv_data, "rtpflags", "rfc2190") ||

                 c->codec_id == AV_CODEC_ID_H263P)

             av_strlcatf(buff, size, "a=rtpmap:%d H263-2000/90000\r\n"
                                     "a=framesize:%d %d-%d\r\n",
                                     payload_type,
                                     payload_type, c->width, c->height);

             break;

         case AV_CODEC_ID_HEVC:
             if (c->extradata_size)

                 config = extradata2psets_hevc(c);

             av_strlcatf(buff, size, "a=rtpmap:%d H265/90000\r\n", payload_type);

             if (config)
                 av_strlcatf(buff, size, "a=fmtp:%d %s\r\n",
                                          payload_type, config);

             break;

         case AV_CODEC_ID_MPEG4:

             if (c->extradata_size) {

                 config = extradata2config(c);

             }
             av_strlcatf(buff, size, "a=rtpmap:%d MP4V-ES/90000\r\n"
                                     "a=fmtp:%d profile-level-id=1%s\r\n",
                                      payload_type,
                                      payload_type, config ? config : "");
             break;

         case AV_CODEC_ID_AAC:

             if (fmt && fmt->oformat && fmt->oformat->priv_class &&

                 av_opt_flag_is_set(fmt->priv_data, "rtpflags", "latm")) {

                 config = latm_context2config(c);
                 if (!config)
                     return NULL;
                 av_strlcatf(buff, size, "a=rtpmap:%d MP4A-LATM/%d/%d\r\n"
                                         "a=fmtp:%d profile-level-id=%d;cpresent=0;config=%s\r\n",
                                          payload_type, c->sample_rate, c->channels,
                                          payload_type, latm_context2profilelevel(c), config);
             } else {

                 if (c->extradata_size) {
                     config = extradata2config(c);
                 } else {
                     /* FIXME: maybe we can forge config information based on the
                      *        codec parameters...
                      */
                     av_log(c, AV_LOG_ERROR, "AAC with no global headers is currently not supported.\n");
                     return NULL;
                 }

                 if (!config) {

                     return NULL;
                 }
                 av_strlcatf(buff, size, "a=rtpmap:%d MPEG4-GENERIC/%d/%d\r\n"
                                         "a=fmtp:%d profile-level-id=1;"
                                         "mode=AAC-hbr;sizelength=13;indexlength=3;"
                                         "indexdeltalength=3%s\r\n",
                                          payload_type, c->sample_rate, c->channels,
                                          payload_type, config);

             }

             break;

         case AV_CODEC_ID_PCM_S16BE:

             if (payload_type >= RTP_PT_PRIVATE)

                 av_strlcatf(buff, size, "a=rtpmap:%d L16/%d/%d\r\n",
                                          payload_type,
                                          c->sample_rate, c->channels);
             break;

         case AV_CODEC_ID_PCM_MULAW:

             if (payload_type >= RTP_PT_PRIVATE)

                 av_strlcatf(buff, size, "a=rtpmap:%d PCMU/%d/%d\r\n",
                                          payload_type,
                                          c->sample_rate, c->channels);
             break;

         case AV_CODEC_ID_PCM_ALAW:

             if (payload_type >= RTP_PT_PRIVATE)

                 av_strlcatf(buff, size, "a=rtpmap:%d PCMA/%d/%d\r\n",
                                          payload_type,
                                          c->sample_rate, c->channels);
             break;

         case AV_CODEC_ID_AMR_NB:

             av_strlcatf(buff, size, "a=rtpmap:%d AMR/%d/%d\r\n"
                                     "a=fmtp:%d octet-align=1\r\n",
                                      payload_type, c->sample_rate, c->channels,
                                      payload_type);
             break;

         case AV_CODEC_ID_AMR_WB:

             av_strlcatf(buff, size, "a=rtpmap:%d AMR-WB/%d/%d\r\n"
                                     "a=fmtp:%d octet-align=1\r\n",
                                      payload_type, c->sample_rate, c->channels,
                                      payload_type);
             break;

         case AV_CODEC_ID_VORBIS:

             if (c->extradata_size)
                 config = xiph_extradata2config(c);
             else
                 av_log(c, AV_LOG_ERROR, "Vorbis configuration info missing\n");
             if (!config)
                 return NULL;
 
             av_strlcatf(buff, size, "a=rtpmap:%d vorbis/%d/%d\r\n"
                                     "a=fmtp:%d configuration=%s\r\n",
                                     payload_type, c->sample_rate, c->channels,
                                     payload_type, config);
             break;

         case AV_CODEC_ID_THEORA: {

             const char *pix_fmt;
             switch (c->pix_fmt) {

             case AV_PIX_FMT_YUV420P:

                 pix_fmt = "YCbCr-4:2:0";
                 break;

             case AV_PIX_FMT_YUV422P:

                 pix_fmt = "YCbCr-4:2:2";
                 break;

             case AV_PIX_FMT_YUV444P:

                 pix_fmt = "YCbCr-4:4:4";
                 break;
             default:
                 av_log(c, AV_LOG_ERROR, "Unsupported pixel format.\n");
                 return NULL;
             }
 

             if (c->extradata_size)
                 config = xiph_extradata2config(c);
             else
                 av_log(c, AV_LOG_ERROR, "Theora configuation info missing\n");
             if (!config)
                 return NULL;
 

             av_strlcatf(buff, size, "a=rtpmap:%d theora/90000\r\n"
                                     "a=fmtp:%d delivery-method=inline; "
                                     "width=%d; height=%d; sampling=%s; "
                                     "configuration=%s\r\n",
                                     payload_type, payload_type,
                                     c->width, c->height, pix_fmt, config);
             break;
         }

         case AV_CODEC_ID_VP8:

             av_strlcatf(buff, size, "a=rtpmap:%d VP8/90000\r\n",
                                      payload_type);
             break;

         case AV_CODEC_ID_MJPEG:
             if (payload_type >= RTP_PT_PRIVATE)
                 av_strlcatf(buff, size, "a=rtpmap:%d JPEG/90000\r\n",
                                          payload_type);
             break;

         case AV_CODEC_ID_ADPCM_G722:

             if (payload_type >= RTP_PT_PRIVATE)
                 av_strlcatf(buff, size, "a=rtpmap:%d G722/%d/%d\r\n",
                                          payload_type,
                                          8000, c->channels);
             break;

         case AV_CODEC_ID_ADPCM_G726: {

             if (payload_type >= RTP_PT_PRIVATE)
                 av_strlcatf(buff, size, "a=rtpmap:%d G726-%d/%d\r\n",
                                          payload_type,
                                          c->bits_per_coded_sample*8,
                                          c->sample_rate);
             break;
         }

         case AV_CODEC_ID_ILBC:

             av_strlcatf(buff, size, "a=rtpmap:%d iLBC/%d\r\n"
                                     "a=fmtp:%d mode=%d\r\n",
                                      payload_type, c->sample_rate,
                                      payload_type, c->block_align == 38 ? 20 : 30);
             break;

         case AV_CODEC_ID_SPEEX:
             av_strlcatf(buff, size, "a=rtpmap:%d speex/%d\r\n",
                                      payload_type, c->sample_rate);

             if (c->codec) {
                 const char *mode;
                 uint64_t vad_option;
 

                 if (c->flags & AV_CODEC_FLAG_QSCALE)

                       mode = "on";
                 else if (!av_opt_get_int(c, "vad", AV_OPT_FLAG_ENCODING_PARAM, &vad_option) && vad_option)
                       mode = "vad";
                 else
                       mode = "off";
 
                 av_strlcatf(buff, size, "a=fmtp:%d vbr=%s\r\n",
                                         payload_type, mode);
             }

             break;

         case AV_CODEC_ID_OPUS:

             /* The opus RTP draft says that all opus streams MUST be declared
                as stereo, to avoid negotiation failures. The actual number of
                channels can change on a packet-by-packet basis. The number of
                channels a receiver prefers to receive or a sender plans to send
                can be declared via fmtp parameters (both default to mono), but
                receivers MUST be able to receive and process stereo packets. */
             av_strlcatf(buff, size, "a=rtpmap:%d opus/48000/2\r\n",

                                      payload_type);

             if (c->channels == 2) {
                 av_strlcatf(buff, size, "a=fmtp:%d sprop-stereo:1\r\n",
                                          payload_type);
             }

             break;

         default:

             /* Nothing special to do here... */

             break;
     }
 
     av_free(config);
 
     return buff;
 }
 

 void ff_sdp_write_media(char *buff, int size, AVStream *st, int idx,
                         const char *dest_addr, const char *dest_type,
                         int port, int ttl, AVFormatContext *fmt)

 {

     AVCodecContext *c = st->codec;

     const char *type;
     int payload_type;
 

     payload_type = ff_rtp_get_payload_type(fmt, c, idx);

 
     switch (c->codec_type) {

         case AVMEDIA_TYPE_VIDEO   : type = "video"      ; break;
         case AVMEDIA_TYPE_AUDIO   : type = "audio"      ; break;
         case AVMEDIA_TYPE_SUBTITLE: type = "text"       ; break;

         default                 : type = "application"; break;
     }
 
     av_strlcatf(buff, size, "m=%s %d RTP/AVP %d\r\n", type, port, payload_type);

     sdp_write_address(buff, size, dest_addr, dest_type, ttl);

     if (c->bit_rate) {
         av_strlcatf(buff, size, "b=AS:%d\r\n", c->bit_rate / 1000);
     }

     sdp_write_media_attributes(buff, size, c, payload_type, fmt);

 }
 

 int av_sdp_create(AVFormatContext *ac[], int n_files, char *buf, int size)

 {

     AVDictionaryEntry *title = av_dict_get(ac[0]->metadata, "title", NULL, 0);

     struct sdp_session_level s = { 0 };

     int i, j, port, ttl, is_multicast, index = 0;

     char dst[32], dst_type[5];

     memset(buf, 0, size);

     s.user = "-";
     s.src_addr = "127.0.0.1";    /* FIXME: Properly set this */

     s.src_type = "IP4";

     s.name = title ? title->value : "No Name";

 
     port = 0;
     ttl = 0;
     if (n_files == 1) {

         port = sdp_get_address(dst, sizeof(dst), &ttl, ac[0]->filename);

         is_multicast = resolve_destination(dst, sizeof(dst), dst_type,
                                            sizeof(dst_type));
         if (!is_multicast)
             ttl = 0;

         if (dst[0]) {

             s.dst_addr = dst;

             s.dst_type = dst_type;

             s.ttl = ttl;

             if (!strcmp(dst_type, "IP6")) {
                 s.src_addr = "::1";
                 s.src_type = "IP6";
             }

         }
     }

     sdp_write_header(buf, size, &s);

 
     dst[0] = 0;
     for (i = 0; i < n_files; i++) {
         if (n_files != 1) {

             port = sdp_get_address(dst, sizeof(dst), &ttl, ac[i]->filename);

             is_multicast = resolve_destination(dst, sizeof(dst), dst_type,
                                                sizeof(dst_type));
             if (!is_multicast)
                 ttl = 0;

         }
         for (j = 0; j < ac[i]->nb_streams; j++) {

             ff_sdp_write_media(buf, size, ac[i]->streams[j], index++,
                                dst[0] ? dst : NULL, dst_type,
                                (port > 0) ? port + j * 2 : 0,
                                ttl, ac[i]);

             if (port <= 0) {

                 av_strlcatf(buf, size,

                                    "a=control:streamid=%d\r\n", i + j);
             }

             if (ac[i]->pb && ac[i]->pb->av_class) {
                 uint8_t *crypto_suite = NULL, *crypto_params = NULL;
                 av_opt_get(ac[i]->pb, "srtp_out_suite",  AV_OPT_SEARCH_CHILDREN,
                            &crypto_suite);
                 av_opt_get(ac[i]->pb, "srtp_out_params", AV_OPT_SEARCH_CHILDREN,
                            &crypto_params);
                 if (crypto_suite && crypto_suite[0])
                     av_strlcatf(buf, size,
                                 "a=crypto:1 %s inline:%s\r\n",
                                 crypto_suite, crypto_params);
                 av_free(crypto_suite);
                 av_free(crypto_params);
             }

         }
     }
 

     return 0;

 }

 #else

 int av_sdp_create(AVFormatContext *ac[], int n_files, char *buf, int size)

 {

     return AVERROR(ENOSYS);

 }

 void ff_sdp_write_media(char *buff, int size, AVStream *st, int idx,
                         const char *dest_addr, const char *dest_type,
                         int port, int ttl, AVFormatContext *fmt)

 {
 }

 #endif