libavformat/sdp.c

   1 /*
   2  * copyright (c) 2007 Luca Abeni
   3  *
   4  * This file is part of Libav.
   5  *
   6  * Libav is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU Lesser General Public
   8  * License as published by the Free Software Foundation; either
   9  * version 2.1 of the License, or (at your option) any later version.
  10  *
  11  * Libav is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14  * Lesser General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU Lesser General Public
  17  * License along with Libav; if not, write to the Free Software
  18  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  19  */
  20
  21 #include <string.h>
  22 #include "libavutil/avstring.h"
  23 #include "libavutil/base64.h"
  24 #include "libavutil/dict.h"
  25 #include "libavutil/parseutils.h"
  26 #include "libavutil/opt.h"
  27 #include "libavcodec/xiph.h"
  28 #include "libavcodec/mpeg4audio.h"
  29 #include "avformat.h"
  30 #include "internal.h"
  31 #include "avc.h"
  32 #include "rtp.h"
  33 #if CONFIG_NETWORK
  34 #include "network.h"
  35 #endif
  36
  37 #if CONFIG_RTP_MUXER
  38 #define MAX_EXTRADATA_SIZE ((INT_MAX - 10) / 2)
  39
  40 struct sdp_session_level {
  41     int sdp_version;      /**< protocol version (currently 0) */
  42     int id;               /**< session ID */
  43     int version;          /**< session version */
  44     int start_time;       /**< session start time (NTP time, in seconds),
  45                                or 0 in case of permanent session */
  46     int end_time;         /**< session end time (NTP time, in seconds),
  47                                or 0 if the session is not bounded */
  48     int ttl;              /**< TTL, in case of multicast stream */
  49     const char *user;     /**< username of the session's creator */
  50     const char *src_addr; /**< IP address of the machine from which the session was created */
  51     const char *src_type; /**< address type of src_addr */
  52     const char *dst_addr; /**< destination IP address (can be multicast) */
  53     const char *dst_type; /**< destination IP address type */
  54     const char *name;     /**< session name (can be an empty string) */
  55 };
  56
  57 static void sdp_write_address(char *buff, int size, const char *dest_addr,
  58                               const char *dest_type, int ttl)
  59 {
  60     if (dest_addr) {
  61         if (!dest_type)
  62             dest_type = "IP4";
  63         if (ttl > 0 && !strcmp(dest_type, "IP4")) {
  64             /* The TTL should only be specified for IPv4 multicast addresses,
  65              * not for IPv6. */
  66             av_strlcatf(buff, size, "c=IN %s %s/%d\r\n", dest_type, dest_addr, ttl);
  67         } else {
  68             av_strlcatf(buff, size, "c=IN %s %s\r\n", dest_type, dest_addr);
  69         }
  70     }
  71 }
  72
  73 static void sdp_write_header(char *buff, int size, struct sdp_session_level *s)
  74 {
  75     av_strlcatf(buff, size, "v=%d\r\n"
  76                             "o=- %d %d IN %s %s\r\n"
  77                             "s=%s\r\n",
  78                             s->sdp_version,
  79                             s->id, s->version, s->src_type, s->src_addr,
  80                             s->name);
  81     sdp_write_address(buff, size, s->dst_addr, s->dst_type, s->ttl);
  82     av_strlcatf(buff, size, "t=%d %d\r\n"
  83                             "a=tool:libavformat " AV_STRINGIFY(LIBAVFORMAT_VERSION) "\r\n",
  84                             s->start_time, s->end_time);
  85 }
  86
  87 #if CONFIG_NETWORK
  88 static int resolve_destination(char *dest_addr, int size, char *type,
  89                                int type_size)
  90 {
  91     struct addrinfo hints, *ai;
  92     int is_multicast;
  93
  94     av_strlcpy(type, "IP4", type_size);
  95     if (!dest_addr[0])
  96         return 0;
  97
  98     /* Resolve the destination, since it must be written
  99      * as a numeric IP address in the SDP. */
 100
 101     memset(&hints, 0, sizeof(hints));
 102     if (getaddrinfo(dest_addr, NULL, &hints, &ai))
 103         return 0;
 104     getnameinfo(ai->ai_addr, ai->ai_addrlen, dest_addr, size,
 105                 NULL, 0, NI_NUMERICHOST);
 106 #ifdef AF_INET6
 107     if (ai->ai_family == AF_INET6)
 108         av_strlcpy(type, "IP6", type_size);
 109 #endif
 110     is_multicast = ff_is_multicast_address(ai->ai_addr);
 111     freeaddrinfo(ai);
 112     return is_multicast;
 113 }
 114 #else
 115 static int resolve_destination(char *dest_addr, int size, char *type,
 116                                int type_size)
 117 {
 118     return 0;
 119 }
 120 #endif
 121
 122 static int sdp_get_address(char *dest_addr, int size, int *ttl, const char *url)
 123 {
 124     int port;
 125     const char *p;
 126     char proto[32];
 127
 128     av_url_split(proto, sizeof(proto), NULL, 0, dest_addr, size, &port, NULL, 0, url);
 129
 130     *ttl = 0;
 131
 132     if (strcmp(proto, "rtp")) {
 133         /* The url isn't for the actual rtp sessions,
 134          * don't parse out anything else than the destination.
 135          */
 136         return 0;
 137     }
 138
 139     p = strchr(url, '?');
 140     if (p) {
 141         char buff[64];
 142
 143         if (av_find_info_tag(buff, sizeof(buff), "ttl", p)) {
 144             *ttl = strtol(buff, NULL, 10);
 145         } else {
 146             *ttl = 5;
 147         }
 148     }
 149
 150     return port;
 151 }
 152
 153 #define MAX_PSET_SIZE 1024
 154 static char *extradata2psets(AVCodecContext *c)
 155 {
 156     char *psets, *p;
 157     const uint8_t *r;
 158     const char *pset_string = "; sprop-parameter-sets=";
 159     uint8_t *orig_extradata = NULL;
 160     int orig_extradata_size = 0;
 161
 162     if (c->extradata_size > MAX_EXTRADATA_SIZE) {
 163         av_log(c, AV_LOG_ERROR, "Too much extradata!\n");
 164
 165         return NULL;
 166     }
 167     if (c->extradata[0] == 1) {
 168         uint8_t *dummy_p;
 169         int dummy_int;
 170         AVBitStreamFilterContext *bsfc= av_bitstream_filter_init("h264_mp4toannexb");
 171
 172         if (!bsfc) {
 173             av_log(c, AV_LOG_ERROR, "Cannot open the h264_mp4toannexb BSF!\n");
 174
 175             return NULL;
 176         }
 177
 178         orig_extradata_size = c->extradata_size;
 179         orig_extradata = av_mallocz(orig_extradata_size +
 180                                     FF_INPUT_BUFFER_PADDING_SIZE);
 181         if (!orig_extradata) {
 182             av_bitstream_filter_close(bsfc);
 183             return NULL;
 184         }
 185         memcpy(orig_extradata, c->extradata, orig_extradata_size);
 186         av_bitstream_filter_filter(bsfc, c, NULL, &dummy_p, &dummy_int, NULL, 0, 0);
 187         av_bitstream_filter_close(bsfc);
 188     }
 189
 190     psets = av_mallocz(MAX_PSET_SIZE);
 191     if (psets == NULL) {
 192         av_log(c, AV_LOG_ERROR, "Cannot allocate memory for the parameter sets.\n");
 193         av_free(orig_extradata);
 194         return NULL;
 195     }
 196     memcpy(psets, pset_string, strlen(pset_string));
 197     p = psets + strlen(pset_string);
 198     r = ff_avc_find_startcode(c->extradata, c->extradata + c->extradata_size);
 199     while (r < c->extradata + c->extradata_size) {
 200         const uint8_t *r1;
 201         uint8_t nal_type;
 202
 203         while (!*(r++));
 204         nal_type = *r & 0x1f;
 205         r1 = ff_avc_find_startcode(r, c->extradata + c->extradata_size);
 206         if (nal_type != 7 && nal_type != 8) { /* Only output SPS and PPS */
 207             r = r1;
 208             continue;
 209         }
 210         if (p != (psets + strlen(pset_string))) {
 211             *p = ',';
 212             p++;
 213         }
 214         if (av_base64_encode(p, MAX_PSET_SIZE - (p - psets), r, r1 - r) == NULL) {
 215             av_log(c, AV_LOG_ERROR, "Cannot Base64-encode %td %td!\n", MAX_PSET_SIZE - (p - psets), r1 - r);
 216             av_free(psets);
 217
 218             return NULL;
 219         }
 220         p += strlen(p);
 221         r = r1;
 222     }
 223     if (orig_extradata) {
 224         av_free(c->extradata);
 225         c->extradata      = orig_extradata;
 226         c->extradata_size = orig_extradata_size;
 227     }
 228
 229     return psets;
 230 }
 231
 232 static char *extradata2config(AVCodecContext *c)
 233 {
 234     char *config;
 235
 236     if (c->extradata_size > MAX_EXTRADATA_SIZE) {
 237         av_log(c, AV_LOG_ERROR, "Too much extradata!\n");
 238
 239         return NULL;
 240     }
 241     config = av_malloc(10 + c->extradata_size * 2);
 242     if (config == NULL) {
 243         av_log(c, AV_LOG_ERROR, "Cannot allocate memory for the config info.\n");
 244         return NULL;
 245     }
 246     memcpy(config, "; config=", 9);
 247     ff_data_to_hex(config + 9, c->extradata, c->extradata_size, 0);
 248     config[9 + c->extradata_size * 2] = 0;
 249
 250     return config;
 251 }
 252
 253 static char *xiph_extradata2config(AVCodecContext *c)
 254 {
 255     char *config, *encoded_config;
 256     uint8_t *header_start[3];
 257     int headers_len, header_len[3], config_len;
 258     int first_header_size;
 259
 260     switch (c->codec_id) {
 261     case CODEC_ID_THEORA:
 262         first_header_size = 42;
 263         break;
 264     case CODEC_ID_VORBIS:
 265         first_header_size = 30;
 266         break;
 267     default:
 268         av_log(c, AV_LOG_ERROR, "Unsupported Xiph codec ID\n");
 269         return NULL;
 270     }
 271
 272     if (avpriv_split_xiph_headers(c->extradata, c->extradata_size,
 273                               first_header_size, header_start,
 274                               header_len) < 0) {
 275         av_log(c, AV_LOG_ERROR, "Extradata corrupt.\n");
 276         return NULL;
 277     }
 278
 279     headers_len = header_len[0] + header_len[2];
 280     config_len = 4 +          // count
 281                  3 +          // ident
 282                  2 +          // packet size
 283                  1 +          // header count
 284                  2 +          // header size
 285                  headers_len; // and the rest
 286
 287     config = av_malloc(config_len);
 288     if (!config)
 289         goto xiph_fail;
 290
 291     encoded_config = av_malloc(AV_BASE64_SIZE(config_len));
 292     if (!encoded_config) {
 293         av_free(config);
 294         goto xiph_fail;
 295     }
 296
 297     config[0] = config[1] = config[2] = 0;
 298     config[3] = 1;
 299     config[4] = (RTP_XIPH_IDENT >> 16) & 0xff;
 300     config[5] = (RTP_XIPH_IDENT >>  8) & 0xff;
 301     config[6] = (RTP_XIPH_IDENT      ) & 0xff;
 302     config[7] = (headers_len >> 8) & 0xff;
 303     config[8] = headers_len & 0xff;
 304     config[9] = 2;
 305     config[10] = header_len[0];
 306     config[11] = 0; // size of comment header; nonexistent
 307     memcpy(config + 12, header_start[0], header_len[0]);
 308     memcpy(config + 12 + header_len[0], header_start[2], header_len[2]);
 309
 310     av_base64_encode(encoded_config, AV_BASE64_SIZE(config_len),
 311                      config, config_len);
 312     av_free(config);
 313
 314     return encoded_config;
 315
 316 xiph_fail:
 317     av_log(c, AV_LOG_ERROR,
 318            "Not enough memory for configuration string\n");
 319     return NULL;
 320 }
 321
 322 static int latm_context2profilelevel(AVCodecContext *c)
 323 {
 324     /* MP4A-LATM
 325      * The RTP payload format specification is described in RFC 3016
 326      * The encoding specifications are provided in ISO/IEC 14496-3 */
 327
 328     int profile_level = 0x2B;
 329
 330     /* TODO: AAC Profile only supports AAC LC Object Type.
 331      * Different Object Types should implement different Profile Levels */
 332
 333     if (c->sample_rate <= 24000) {
 334         if (c->channels <= 2)
 335             profile_level = 0x28; // AAC Profile, Level 1
 336     } else if (c->sample_rate <= 48000) {
 337         if (c->channels <= 2) {
 338             profile_level = 0x29; // AAC Profile, Level 2
 339         } else if (c->channels <= 5) {
 340             profile_level = 0x2A; // AAC Profile, Level 4
 341         }
 342     } else if (c->sample_rate <= 96000) {
 343         if (c->channels <= 5) {
 344             profile_level = 0x2B; // AAC Profile, Level 5
 345         }
 346     }
 347
 348     return profile_level;
 349 }
 350
 351 static char *latm_context2config(AVCodecContext *c)
 352 {
 353     /* MP4A-LATM
 354      * The RTP payload format specification is described in RFC 3016
 355      * The encoding specifications are provided in ISO/IEC 14496-3 */
 356
 357     uint8_t config_byte[6];
 358     int rate_index;
 359     char *config;
 360
 361     for (rate_index = 0; rate_index < 16; rate_index++)
 362         if (avpriv_mpeg4audio_sample_rates[rate_index] == c->sample_rate)
 363             break;
 364     if (rate_index == 16) {
 365         av_log(c, AV_LOG_ERROR, "Unsupported sample rate\n");
 366         return NULL;
 367     }
 368
 369     config_byte[0] = 0x40;
 370     config_byte[1] = 0;
 371     config_byte[2] = 0x20 | rate_index;
 372     config_byte[3] = c->channels << 4;
 373     config_byte[4] = 0x3f;
 374     config_byte[5] = 0xc0;
 375
 376     config = av_malloc(6*2+1);
 377     if (!config) {
 378         av_log(c, AV_LOG_ERROR, "Cannot allocate memory for the config info.\n");
 379         return NULL;
 380     }
 381     ff_data_to_hex(config, config_byte, 6, 1);
 382     config[12] = 0;
 383
 384     return config;
 385 }
 386
 387 static char *sdp_write_media_attributes(char *buff, int size, AVCodecContext *c, int payload_type, AVFormatContext *fmt)
 388 {
 389     char *config = NULL;
 390
 391     switch (c->codec_id) {
 392         case CODEC_ID_H264:
 393             if (c->extradata_size) {
 394                 config = extradata2psets(c);
 395             }
 396             av_strlcatf(buff, size, "a=rtpmap:%d H264/90000\r\n"
 397                                     "a=fmtp:%d packetization-mode=1%s\r\n",
 398                                      payload_type,
 399                                      payload_type, config ? config : "");
 400             break;
 401         case CODEC_ID_H263:
 402         case CODEC_ID_H263P:
 403             /* a=framesize is required by 3GPP TS 26.234 (PSS). It
 404              * actually specifies the maximum video size, but we only know
 405              * the current size. This is required for playback on Android
 406              * stagefright and on Samsung bada. */
 407             av_strlcatf(buff, size, "a=rtpmap:%d H263-2000/90000\r\n"
 408                                     "a=framesize:%d %d-%d\r\n",
 409                                     payload_type,
 410                                     payload_type, c->width, c->height);
 411             break;
 412         case CODEC_ID_MPEG4:
 413             if (c->extradata_size) {
 414                 config = extradata2config(c);
 415             }
 416             av_strlcatf(buff, size, "a=rtpmap:%d MP4V-ES/90000\r\n"
 417                                     "a=fmtp:%d profile-level-id=1%s\r\n",
 418                                      payload_type,
 419                                      payload_type, config ? config : "");
 420             break;
 421         case CODEC_ID_AAC:
 422             if (fmt && fmt->oformat->priv_class &&
 423                 av_opt_flag_is_set(fmt->priv_data, "rtpflags", "latm")) {
 424                 config = latm_context2config(c);
 425                 if (!config)
 426                     return NULL;
 427                 av_strlcatf(buff, size, "a=rtpmap:%d MP4A-LATM/%d/%d\r\n"
 428                                         "a=fmtp:%d profile-level-id=%d;cpresent=0;config=%s\r\n",
 429                                          payload_type, c->sample_rate, c->channels,
 430                                          payload_type, latm_context2profilelevel(c), config);
 431             } else {
 432                 if (c->extradata_size) {
 433                     config = extradata2config(c);
 434                 } else {
 435                     /* FIXME: maybe we can forge config information based on the
 436                      *        codec parameters...
 437                      */
 438                     av_log(c, AV_LOG_ERROR, "AAC with no global headers is currently not supported.\n");
 439                     return NULL;
 440                 }
 441                 if (config == NULL) {
 442                     return NULL;
 443                 }
 444                 av_strlcatf(buff, size, "a=rtpmap:%d MPEG4-GENERIC/%d/%d\r\n"
 445                                         "a=fmtp:%d profile-level-id=1;"
 446                                         "mode=AAC-hbr;sizelength=13;indexlength=3;"
 447                                         "indexdeltalength=3%s\r\n",
 448                                          payload_type, c->sample_rate, c->channels,
 449                                          payload_type, config);
 450             }
 451             break;
 452         case CODEC_ID_PCM_S16BE:
 453             if (payload_type >= RTP_PT_PRIVATE)
 454                 av_strlcatf(buff, size, "a=rtpmap:%d L16/%d/%d\r\n",
 455                                          payload_type,
 456                                          c->sample_rate, c->channels);
 457             break;
 458         case CODEC_ID_PCM_MULAW:
 459             if (payload_type >= RTP_PT_PRIVATE)
 460                 av_strlcatf(buff, size, "a=rtpmap:%d PCMU/%d/%d\r\n",
 461                                          payload_type,
 462                                          c->sample_rate, c->channels);
 463             break;
 464         case CODEC_ID_PCM_ALAW:
 465             if (payload_type >= RTP_PT_PRIVATE)
 466                 av_strlcatf(buff, size, "a=rtpmap:%d PCMA/%d/%d\r\n",
 467                                          payload_type,
 468                                          c->sample_rate, c->channels);
 469             break;
 470         case CODEC_ID_AMR_NB:
 471             av_strlcatf(buff, size, "a=rtpmap:%d AMR/%d/%d\r\n"
 472                                     "a=fmtp:%d octet-align=1\r\n",
 473                                      payload_type, c->sample_rate, c->channels,
 474                                      payload_type);
 475             break;
 476         case CODEC_ID_AMR_WB:
 477             av_strlcatf(buff, size, "a=rtpmap:%d AMR-WB/%d/%d\r\n"
 478                                     "a=fmtp:%d octet-align=1\r\n",
 479                                      payload_type, c->sample_rate, c->channels,
 480                                      payload_type);
 481             break;
 482         case CODEC_ID_VORBIS:
 483             if (c->extradata_size)
 484                 config = xiph_extradata2config(c);
 485             else
 486                 av_log(c, AV_LOG_ERROR, "Vorbis configuration info missing\n");
 487             if (!config)
 488                 return NULL;
 489
 490             av_strlcatf(buff, size, "a=rtpmap:%d vorbis/%d/%d\r\n"
 491                                     "a=fmtp:%d configuration=%s\r\n",
 492                                     payload_type, c->sample_rate, c->channels,
 493                                     payload_type, config);
 494             break;
 495         case CODEC_ID_THEORA: {
 496             const char *pix_fmt;
 497             if (c->extradata_size)
 498                 config = xiph_extradata2config(c);
 499             else
 500                 av_log(c, AV_LOG_ERROR, "Theora configuation info missing\n");
 501             if (!config)
 502                 return NULL;
 503
 504             switch (c->pix_fmt) {
 505             case PIX_FMT_YUV420P:
 506                 pix_fmt = "YCbCr-4:2:0";
 507                 break;
 508             case PIX_FMT_YUV422P:
 509                 pix_fmt = "YCbCr-4:2:2";
 510                 break;
 511             case PIX_FMT_YUV444P:
 512                 pix_fmt = "YCbCr-4:4:4";
 513                 break;
 514             default:
 515                 av_log(c, AV_LOG_ERROR, "Unsupported pixel format.\n");
 516                 return NULL;
 517             }
 518
 519             av_strlcatf(buff, size, "a=rtpmap:%d theora/90000\r\n"
 520                                     "a=fmtp:%d delivery-method=inline; "
 521                                     "width=%d; height=%d; sampling=%s; "
 522                                     "configuration=%s\r\n",
 523                                     payload_type, payload_type,
 524                                     c->width, c->height, pix_fmt, config);
 525             break;
 526         }
 527         case CODEC_ID_VP8:
 528             av_strlcatf(buff, size, "a=rtpmap:%d VP8/90000\r\n",
 529                                      payload_type);
 530             break;
 531         case CODEC_ID_ADPCM_G722:
 532             if (payload_type >= RTP_PT_PRIVATE)
 533                 av_strlcatf(buff, size, "a=rtpmap:%d G722/%d/%d\r\n",
 534                                          payload_type,
 535                                          8000, c->channels);
 536             break;
 537         case CODEC_ID_ADPCM_G726: {
 538             if (payload_type >= RTP_PT_PRIVATE)
 539                 av_strlcatf(buff, size, "a=rtpmap:%d G726-%d/%d\r\n",
 540                                          payload_type,
 541                                          c->bits_per_coded_sample*8,
 542                                          c->sample_rate);
 543             break;
 544         }
 545         default:
 546             /* Nothing special to do here... */
 547             break;
 548     }
 549
 550     av_free(config);
 551
 552     return buff;
 553 }
 554
 555 void ff_sdp_write_media(char *buff, int size, AVCodecContext *c, const char *dest_addr, const char *dest_type, int port, int ttl, AVFormatContext *fmt)
 556 {
 557     const char *type;
 558     int payload_type;
 559
 560     payload_type = ff_rtp_get_payload_type(fmt, c);
 561
 562     switch (c->codec_type) {
 563         case AVMEDIA_TYPE_VIDEO   : type = "video"      ; break;
 564         case AVMEDIA_TYPE_AUDIO   : type = "audio"      ; break;
 565         case AVMEDIA_TYPE_SUBTITLE: type = "text"       ; break;
 566         default                 : type = "application"; break;
 567     }
 568
 569     av_strlcatf(buff, size, "m=%s %d RTP/AVP %d\r\n", type, port, payload_type);
 570     sdp_write_address(buff, size, dest_addr, dest_type, ttl);
 571     if (c->bit_rate) {
 572         av_strlcatf(buff, size, "b=AS:%d\r\n", c->bit_rate / 1000);
 573     }
 574
 575     sdp_write_media_attributes(buff, size, c, payload_type, fmt);
 576 }
 577
 578 int av_sdp_create(AVFormatContext *ac[], int n_files, char *buf, int size)
 579 {
 580     AVDictionaryEntry *title = av_dict_get(ac[0]->metadata, "title", NULL, 0);
 581     struct sdp_session_level s;
 582     int i, j, port, ttl, is_multicast;
 583     char dst[32], dst_type[5];
 584
 585     memset(buf, 0, size);
 586     memset(&s, 0, sizeof(struct sdp_session_level));
 587     s.user = "-";
 588     s.src_addr = "127.0.0.1";    /* FIXME: Properly set this */
 589     s.src_type = "IP4";
 590     s.name = title ? title->value : "No Name";
 591
 592     port = 0;
 593     ttl = 0;
 594     if (n_files == 1) {
 595         port = sdp_get_address(dst, sizeof(dst), &ttl, ac[0]->filename);
 596         is_multicast = resolve_destination(dst, sizeof(dst), dst_type,
 597                                            sizeof(dst_type));
 598         if (!is_multicast)
 599             ttl = 0;
 600         if (dst[0]) {
 601             s.dst_addr = dst;
 602             s.dst_type = dst_type;
 603             s.ttl = ttl;
 604             if (!strcmp(dst_type, "IP6")) {
 605                 s.src_addr = "::1";
 606                 s.src_type = "IP6";
 607             }
 608         }
 609     }
 610     sdp_write_header(buf, size, &s);
 611
 612     dst[0] = 0;
 613     for (i = 0; i < n_files; i++) {
 614         if (n_files != 1) {
 615             port = sdp_get_address(dst, sizeof(dst), &ttl, ac[i]->filename);
 616             is_multicast = resolve_destination(dst, sizeof(dst), dst_type,
 617                                                sizeof(dst_type));
 618             if (!is_multicast)
 619                 ttl = 0;
 620         }
 621         for (j = 0; j < ac[i]->nb_streams; j++) {
 622             ff_sdp_write_media(buf, size,
 623                                   ac[i]->streams[j]->codec, dst[0] ? dst : NULL,
 624                                   dst_type, (port > 0) ? port + j * 2 : 0, ttl,
 625                                   ac[i]);
 626             if (port <= 0) {
 627                 av_strlcatf(buf, size,
 628                                    "a=control:streamid=%d\r\n", i + j);
 629             }
 630         }
 631     }
 632
 633     return 0;
 634 }
 635 #else
 636 int av_sdp_create(AVFormatContext *ac[], int n_files, char *buf, int size)
 637 {
 638     return AVERROR(ENOSYS);
 639 }
 640
 641 void ff_sdp_write_media(char *buff, int size, AVCodecContext *c, const char *dest_addr, const char *dest_type, int port, int ttl, AVFormatContext *fmt)
 642 {
 643 }
 644 #endif
 645
 646 #if FF_API_SDP_CREATE
 647 int avf_sdp_create(AVFormatContext *ac[], int n_files, char *buff, int size)
 648 {
 649     return av_sdp_create(ac, n_files, buff, size);
 650 }
 651 #endif