libavformat/rtpproto.c

   1 /*
   2  * RTP network protocol
   3  * Copyright (c) 2002 Fabrice Bellard
   4  *
   5  * This file is part of FFmpeg.
   6  *
   7  * FFmpeg is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU Lesser General Public
   9  * License as published by the Free Software Foundation; either
  10  * version 2.1 of the License, or (at your option) any later version.
  11  *
  12  * FFmpeg is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15  * Lesser General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU Lesser General Public
  18  * License along with FFmpeg; if not, write to the Free Software
  19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  20  */
  21
  22 /**
  23  * @file
  24  * RTP protocol
  25  */
  26
  27 #include "libavutil/mem.h"
  28 #include "libavutil/parseutils.h"
  29 #include "libavutil/avstring.h"
  30 #include "libavutil/opt.h"
  31 #include "avformat.h"
  32 #include "internal.h"
  33 #include "rtp.h"
  34 #include "rtpproto.h"
  35 #include "url.h"
  36 #include "ip.h"
  37
  38 #include <stdarg.h>
  39 #include "network.h"
  40 #include "os_support.h"
  41 #include <fcntl.h>
  42 #if HAVE_POLL_H
  43 #include <poll.h>
  44 #endif
  45
  46 typedef struct RTPContext {
  47     const AVClass *class;
  48     URLContext *rtp_hd, *rtcp_hd, *fec_hd;
  49     int rtp_fd, rtcp_fd;
  50     IPSourceFilters filters;
  51     int write_to_source;
  52     struct sockaddr_storage last_rtp_source, last_rtcp_source;
  53     socklen_t last_rtp_source_len, last_rtcp_source_len;
  54     int ttl;
  55     int buffer_size;
  56     int rtcp_port, local_rtpport, local_rtcpport;
  57     int connect;
  58     int pkt_size;
  59     int dscp;
  60     char *sources;
  61     char *block;
  62     char *fec_options_str;
  63     int64_t rw_timeout;
  64     char *localaddr;
  65 } RTPContext;
  66
  67 #define OFFSET(x) offsetof(RTPContext, x)
  68 #define D AV_OPT_FLAG_DECODING_PARAM
  69 #define E AV_OPT_FLAG_ENCODING_PARAM
  70 #define DEPR AV_OPT_FLAG_DEPRECATED
  71 static const AVOption options[] = {
  72     { "ttl",                "Time to live (multicast only)",                                    OFFSET(ttl),             AV_OPT_TYPE_INT,    { .i64 = -1 },    -1, 255,     .flags = D|E },
  73     { "buffer_size",        "Send/Receive buffer size (in bytes)",                              OFFSET(buffer_size),     AV_OPT_TYPE_INT,    { .i64 = -1 },    -1, INT_MAX, .flags = D|E },
  74     { "rtcp_port",          "Custom rtcp port",                                                 OFFSET(rtcp_port),       AV_OPT_TYPE_INT,    { .i64 = -1 },    -1, INT_MAX, .flags = D|E },
  75     { "rtcpport",           "Custom rtcp port",                                                 OFFSET(rtcp_port),       AV_OPT_TYPE_INT,    { .i64 = -1 },    -1, INT_MAX, .flags = D|E },
  76     { "local_rtpport",      "Local rtp port",                                                   OFFSET(local_rtpport),   AV_OPT_TYPE_INT,    { .i64 = -1 },    -1, INT_MAX, .flags = D|E },
  77     { "localrtpport",       "Local rtp port",                                                   OFFSET(local_rtpport),   AV_OPT_TYPE_INT,    { .i64 = -1 },    -1, INT_MAX, .flags = D|E },
  78     { "localport",          "Local rtp port",                                                   OFFSET(local_rtpport),   AV_OPT_TYPE_INT,    { .i64 = -1 },    -1, INT_MAX, .flags = D|E|DEPR },
  79     { "local_rtcpport",     "Local rtcp port",                                                  OFFSET(local_rtcpport),  AV_OPT_TYPE_INT,    { .i64 = -1 },    -1, INT_MAX, .flags = D|E },
  80     { "localrtcpport",      "Local rtcp port",                                                  OFFSET(local_rtcpport),  AV_OPT_TYPE_INT,    { .i64 = -1 },    -1, INT_MAX, .flags = D|E },
  81     { "connect",            "Connect socket",                                                   OFFSET(connect),         AV_OPT_TYPE_BOOL,   { .i64 =  0 },     0, 1,       .flags = D|E },
  82     { "write_to_source",    "Send packets to the source address of the latest received packet", OFFSET(write_to_source), AV_OPT_TYPE_BOOL,   { .i64 =  0 },     0, 1,       .flags = D|E },
  83     { "pkt_size",           "Maximum packet size",                                              OFFSET(pkt_size),        AV_OPT_TYPE_INT,    { .i64 = -1 },    -1, INT_MAX, .flags = D|E },
  84     { "dscp",               "DSCP class",                                                       OFFSET(dscp),            AV_OPT_TYPE_INT,    { .i64 = -1 },    -1, INT_MAX, .flags = D|E },
  85     { "timeout",            "set timeout (in microseconds) of socket I/O operations",           OFFSET(rw_timeout),      AV_OPT_TYPE_INT64,  { .i64 = -1 },    -1, INT64_MAX, .flags = D|E },
  86     { "sources",            "Source list",                                                      OFFSET(sources),         AV_OPT_TYPE_STRING, { .str = NULL },               .flags = D|E },
  87     { "block",              "Block list",                                                       OFFSET(block),           AV_OPT_TYPE_STRING, { .str = NULL },               .flags = D|E },
  88     { "fec",                "FEC",                                                              OFFSET(fec_options_str), AV_OPT_TYPE_STRING, { .str = NULL },               .flags = E },
  89     { "localaddr",          "Local address",                                                    OFFSET(localaddr),       AV_OPT_TYPE_STRING, { .str = NULL },               .flags = D|E },
  90     { NULL }
  91 };
  92
  93 static const AVClass rtp_class = {
  94     .class_name = "rtp",
  95     .item_name  = av_default_item_name,
  96     .option     = options,
  97     .version    = LIBAVUTIL_VERSION_INT,
  98 };
  99
 100 /**
 101  * If no filename is given to av_open_input_file because you want to
 102  * get the local port first, then you must call this function to set
 103  * the remote server address.
 104  *
 105  * @param h media file context
 106  * @param uri of the remote server
 107  * @return zero if no error.
 108  */
 109
 110 int ff_rtp_set_remote_url(URLContext *h, const char *uri)
 111 {
 112     RTPContext *s = h->priv_data;
 113     char hostname[256];
 114     int port, rtcp_port;
 115     const char *p;
 116
 117     char buf[1024];
 118     char path[1024];
 119
 120     av_url_split(NULL, 0, NULL, 0, hostname, sizeof(hostname), &port,
 121                  path, sizeof(path), uri);
 122     rtcp_port = port + 1;
 123
 124     p = strchr(uri, '?');
 125     if (p) {
 126         if (av_find_info_tag(buf, sizeof(buf), "rtcpport", p)) {
 127             rtcp_port = strtol(buf, NULL, 10);
 128         }
 129     }
 130
 131     ff_url_join(buf, sizeof(buf), "udp", NULL, hostname, port, "%s", path);
 132     ff_udp_set_remote_url(s->rtp_hd, buf);
 133
 134     ff_url_join(buf, sizeof(buf), "udp", NULL, hostname, rtcp_port, "%s", path);
 135     ff_udp_set_remote_url(s->rtcp_hd, buf);
 136     return 0;
 137 }
 138
 139 static int get_port(const struct sockaddr_storage *ss)
 140 {
 141     if (ss->ss_family == AF_INET)
 142         return ntohs(((const struct sockaddr_in *)ss)->sin_port);
 143 #if HAVE_STRUCT_SOCKADDR_IN6
 144     if (ss->ss_family == AF_INET6)
 145         return ntohs(((const struct sockaddr_in6 *)ss)->sin6_port);
 146 #endif
 147     return 0;
 148 }
 149
 150 static void set_port(struct sockaddr_storage *ss, int port)
 151 {
 152     if (ss->ss_family == AF_INET)
 153         ((struct sockaddr_in *)ss)->sin_port = htons(port);
 154 #if HAVE_STRUCT_SOCKADDR_IN6
 155     else if (ss->ss_family == AF_INET6)
 156         ((struct sockaddr_in6 *)ss)->sin6_port = htons(port);
 157 #endif
 158 }
 159
 160 /**
 161  * add option to url of the form:
 162  * "http://host:port/path?option1=val1&option2=val2...
 163  */
 164
 165 static av_printf_format(3, 4) void url_add_option(char *buf, int buf_size, const char *fmt, ...)
 166 {
 167     char buf1[1024];
 168     va_list ap;
 169
 170     va_start(ap, fmt);
 171     if (strchr(buf, '?'))
 172         av_strlcat(buf, "&", buf_size);
 173     else
 174         av_strlcat(buf, "?", buf_size);
 175     vsnprintf(buf1, sizeof(buf1), fmt, ap);
 176     av_strlcat(buf, buf1, buf_size);
 177     va_end(ap);
 178 }
 179
 180 static void build_udp_url(RTPContext *s,
 181                           char *buf, int buf_size,
 182                           const char *hostname,
 183                           const char *localaddr,
 184                           int port, int local_port,
 185                           const char *include_sources,
 186                           const char *exclude_sources)
 187 {
 188     ff_url_join(buf, buf_size, "udp", NULL, hostname, port, NULL);
 189     if (local_port >= 0)
 190         url_add_option(buf, buf_size, "localport=%d", local_port);
 191     if (s->ttl >= 0)
 192         url_add_option(buf, buf_size, "ttl=%d", s->ttl);
 193     if (s->buffer_size >= 0)
 194         url_add_option(buf, buf_size, "buffer_size=%d", s->buffer_size);
 195     if (s->pkt_size >= 0)
 196         url_add_option(buf, buf_size, "pkt_size=%d", s->pkt_size);
 197     if (s->connect)
 198         url_add_option(buf, buf_size, "connect=1");
 199     if (s->dscp >= 0)
 200         url_add_option(buf, buf_size, "dscp=%d", s->dscp);
 201     url_add_option(buf, buf_size, "fifo_size=0");
 202     if (include_sources && include_sources[0])
 203         url_add_option(buf, buf_size, "sources=%s", include_sources);
 204     if (exclude_sources && exclude_sources[0])
 205         url_add_option(buf, buf_size, "block=%s", exclude_sources);
 206     if (localaddr && localaddr[0])
 207         url_add_option(buf, buf_size, "localaddr=%s", localaddr);
 208 }
 209
 210 /**
 211  * url syntax: rtp://host:port[?option=val...]
 212  * option: 'ttl=n'            : set the ttl value (for multicast only)
 213  *         'rtcpport=n'       : set the remote rtcp port to n
 214  *         'localrtpport=n'   : set the local rtp port to n
 215  *         'localrtcpport=n'  : set the local rtcp port to n
 216  *         'pkt_size=n'       : set max packet size
 217  *         'connect=0/1'      : do a connect() on the UDP socket
 218  *         'sources=ip[,ip]'  : list allowed source IP addresses
 219  *         'block=ip[,ip]'    : list disallowed source IP addresses
 220  *         'write_to_source=0/1' : send packets to the source address of the latest received packet
 221  *         'dscp=n'           : set DSCP value to n (QoS)
 222  * deprecated option:
 223  *         'localport=n'      : set the local port to n
 224  *
 225  * if rtcpport isn't set the rtcp port will be the rtp port + 1
 226  * if local rtp port isn't set any available port will be used for the local
 227  * rtp and rtcp ports
 228  * if the local rtcp port is not set it will be the local rtp port + 1
 229  */
 230
 231 static int rtp_open(URLContext *h, const char *uri, int flags)
 232 {
 233     RTPContext *s = h->priv_data;
 234     AVDictionary *fec_opts = NULL;
 235     int rtp_port;
 236     char hostname[256];
 237     char *fec_protocol = NULL;
 238     char buf[1024];
 239     char path[1024];
 240     const char *p;
 241     int i, max_retry_count = 3;
 242     int rtcpflags;
 243     int ret;
 244
 245     av_url_split(NULL, 0, NULL, 0, hostname, sizeof(hostname), &rtp_port,
 246                  path, sizeof(path), uri);
 247     /* extract parameters */
 248     if (s->rtcp_port < 0)
 249         s->rtcp_port = rtp_port + 1;
 250
 251     p = strchr(uri, '?');
 252     if (p) {
 253         ret = ff_parse_opts_from_query_string(s, p, 1);
 254         if (ret < 0)
 255             goto fail;
 256     }
 257     if (s->sources) {
 258         if ((ret = ff_ip_parse_sources(h, s->sources, &s->filters)) < 0)
 259             goto fail;
 260     }
 261     if (s->block) {
 262         if ((ret = ff_ip_parse_blocks(h, s->block, &s->filters)) < 0)
 263             goto fail;
 264     }
 265     if (s->rw_timeout >= 0)
 266         h->rw_timeout = s->rw_timeout;
 267
 268     if (s->fec_options_str) {
 269         p = s->fec_options_str;
 270
 271         if (!(fec_protocol = av_get_token(&p, "="))) {
 272             av_log(h, AV_LOG_ERROR, "Failed to parse the FEC protocol value\n");
 273             ret = AVERROR(EINVAL);
 274             goto fail;
 275         }
 276         if (strcmp(fec_protocol, "prompeg")) {
 277             av_log(h, AV_LOG_ERROR, "Unsupported FEC protocol %s\n", fec_protocol);
 278             ret = AVERROR(EINVAL);
 279             goto fail;
 280         }
 281
 282         p = s->fec_options_str + strlen(fec_protocol);
 283         while (*p && *p == '=') p++;
 284
 285         if (av_dict_parse_string(&fec_opts, p, "=", ":", 0) < 0) {
 286             av_log(h, AV_LOG_ERROR, "Failed to parse the FEC options\n");
 287             ret = AVERROR(EINVAL);
 288             goto fail;
 289         }
 290         if (s->ttl > 0) {
 291             av_dict_set_int(&fec_opts, "ttl", s->ttl, 0);
 292         }
 293     }
 294
 295     for (i = 0; i < max_retry_count; i++) {
 296         const char *sources = s->sources ? s->sources : "";
 297         const char *block = s->block ? s->block : "";
 298         build_udp_url(s, buf, sizeof(buf),
 299                       hostname, s->localaddr, rtp_port, s->local_rtpport,
 300                       sources, block);
 301         ret = ffurl_open_whitelist(&s->rtp_hd, buf, flags, &h->interrupt_callback,
 302                                    NULL, h->protocol_whitelist, h->protocol_blacklist, h);
 303         if (ret < 0)
 304             goto fail;
 305         s->local_rtpport = ff_udp_get_local_port(s->rtp_hd);
 306         if(s->local_rtpport == 65535) {
 307             s->local_rtpport = -1;
 308             continue;
 309         }
 310         rtcpflags = flags | AVIO_FLAG_WRITE;
 311         if (s->local_rtcpport < 0) {
 312             s->local_rtcpport = s->local_rtpport + 1;
 313             build_udp_url(s, buf, sizeof(buf),
 314                           hostname, s->localaddr, s->rtcp_port, s->local_rtcpport,
 315                           sources, block);
 316             if (ffurl_open_whitelist(&s->rtcp_hd, buf, rtcpflags,
 317                                      &h->interrupt_callback, NULL,
 318                                      h->protocol_whitelist, h->protocol_blacklist, h) < 0) {
 319                 s->local_rtpport = s->local_rtcpport = -1;
 320                 continue;
 321             }
 322             break;
 323         }
 324         build_udp_url(s, buf, sizeof(buf),
 325                       hostname, s->localaddr, s->rtcp_port, s->local_rtcpport,
 326                       sources, block);
 327         ret = ffurl_open_whitelist(&s->rtcp_hd, buf, rtcpflags, &h->interrupt_callback,
 328                                    NULL, h->protocol_whitelist, h->protocol_blacklist, h);
 329         if (ret < 0)
 330             goto fail;
 331         break;
 332     }
 333
 334     s->fec_hd = NULL;
 335     if (fec_protocol) {
 336         ff_url_join(buf, sizeof(buf), fec_protocol, NULL, hostname, rtp_port, NULL);
 337         ret = ffurl_open_whitelist(&s->fec_hd, buf, flags, &h->interrupt_callback,
 338                                    &fec_opts, h->protocol_whitelist, h->protocol_blacklist, h);
 339         if (ret < 0)
 340             goto fail;
 341     }
 342
 343     /* just to ease handle access. XXX: need to suppress direct handle
 344        access */
 345     s->rtp_fd = ffurl_get_file_handle(s->rtp_hd);
 346     s->rtcp_fd = ffurl_get_file_handle(s->rtcp_hd);
 347
 348     h->max_packet_size = s->rtp_hd->max_packet_size;
 349     h->is_streamed = 1;
 350
 351     av_free(fec_protocol);
 352     av_dict_free(&fec_opts);
 353
 354     return 0;
 355
 356  fail:
 357     ff_ip_reset_filters(&s->filters);
 358     ffurl_closep(&s->rtp_hd);
 359     ffurl_closep(&s->rtcp_hd);
 360     ffurl_closep(&s->fec_hd);
 361     av_free(fec_protocol);
 362     av_dict_free(&fec_opts);
 363     return ret;
 364 }
 365
 366 static int rtp_read(URLContext *h, uint8_t *buf, int size)
 367 {
 368     RTPContext *s = h->priv_data;
 369     int len, n, i;
 370     struct pollfd p[2] = {{s->rtp_fd, POLLIN, 0}, {s->rtcp_fd, POLLIN, 0}};
 371     int poll_delay = h->flags & AVIO_FLAG_NONBLOCK ? 0 : POLLING_TIME;
 372     struct sockaddr_storage *addrs[2] = { &s->last_rtp_source, &s->last_rtcp_source };
 373     socklen_t *addr_lens[2] = { &s->last_rtp_source_len, &s->last_rtcp_source_len };
 374     int runs = h->rw_timeout / 1000 / POLLING_TIME;
 375
 376     for(;;) {
 377         if (ff_check_interrupt(&h->interrupt_callback))
 378             return AVERROR_EXIT;
 379         n = poll(p, 2, poll_delay);
 380         if (n > 0) {
 381             /* first try RTCP, then RTP */
 382             for (i = 1; i >= 0; i--) {
 383                 if (!(p[i].revents & POLLIN))
 384                     continue;
 385                 *addr_lens[i] = sizeof(*addrs[i]);
 386                 len = recvfrom(p[i].fd, buf, size, 0,
 387                                 (struct sockaddr *)addrs[i], addr_lens[i]);
 388                 if (len < 0) {
 389                     if (ff_neterrno() == AVERROR(EAGAIN) ||
 390                         ff_neterrno() == AVERROR(EINTR))
 391                         continue;
 392                     return AVERROR(EIO);
 393                 }
 394                 if (ff_ip_check_source_lists(addrs[i], &s->filters))
 395                     continue;
 396                 return len;
 397             }
 398         } else if (n == 0 && h->rw_timeout > 0 && --runs <= 0) {
 399             return AVERROR(ETIMEDOUT);
 400         } else if (n < 0) {
 401             if (ff_neterrno() == AVERROR(EINTR))
 402                 continue;
 403             return AVERROR(EIO);
 404         }
 405         if (h->flags & AVIO_FLAG_NONBLOCK)
 406             return AVERROR(EAGAIN);
 407     }
 408 }
 409
 410 static int rtp_write(URLContext *h, const uint8_t *buf, int size)
 411 {
 412     RTPContext *s = h->priv_data;
 413     int ret, ret_fec;
 414     URLContext *hd;
 415
 416     if (size < 2)
 417         return AVERROR(EINVAL);
 418
 419     if ((buf[0] & 0xc0) != (RTP_VERSION << 6))
 420         av_log(h, AV_LOG_WARNING, "Data doesn't look like RTP packets, "
 421                                   "make sure the RTP muxer is used\n");
 422
 423     if (s->write_to_source) {
 424         int fd;
 425         struct sockaddr_storage *source, temp_source;
 426         socklen_t *source_len, temp_len;
 427         if (!s->last_rtp_source.ss_family && !s->last_rtcp_source.ss_family) {
 428             av_log(h, AV_LOG_ERROR,
 429                    "Unable to send packet to source, no packets received yet\n");
 430             // Intentionally not returning an error here
 431             return size;
 432         }
 433
 434         if (RTP_PT_IS_RTCP(buf[1])) {
 435             fd = s->rtcp_fd;
 436             source     = &s->last_rtcp_source;
 437             source_len = &s->last_rtcp_source_len;
 438         } else {
 439             fd = s->rtp_fd;
 440             source     = &s->last_rtp_source;
 441             source_len = &s->last_rtp_source_len;
 442         }
 443         if (!source->ss_family) {
 444             source      = &temp_source;
 445             source_len  = &temp_len;
 446             if (RTP_PT_IS_RTCP(buf[1])) {
 447                 temp_source = s->last_rtp_source;
 448                 temp_len    = s->last_rtp_source_len;
 449                 set_port(source, get_port(source) + 1);
 450                 av_log(h, AV_LOG_INFO,
 451                        "Not received any RTCP packets yet, inferring peer port "
 452                        "from the RTP port\n");
 453             } else {
 454                 temp_source = s->last_rtcp_source;
 455                 temp_len    = s->last_rtcp_source_len;
 456                 set_port(source, get_port(source) - 1);
 457                 av_log(h, AV_LOG_INFO,
 458                        "Not received any RTP packets yet, inferring peer port "
 459                        "from the RTCP port\n");
 460             }
 461         }
 462
 463         if (!(h->flags & AVIO_FLAG_NONBLOCK)) {
 464             ret = ff_network_wait_fd(fd, 1);
 465             if (ret < 0)
 466                 return ret;
 467         }
 468         ret = sendto(fd, buf, size, 0, (struct sockaddr *) source,
 469                      *source_len);
 470
 471         return ret < 0 ? ff_neterrno() : ret;
 472     }
 473
 474     if (RTP_PT_IS_RTCP(buf[1])) {
 475         /* RTCP payload type */
 476         hd = s->rtcp_hd;
 477     } else {
 478         /* RTP payload type */
 479         hd = s->rtp_hd;
 480     }
 481
 482     if ((ret = ffurl_write(hd, buf, size)) < 0) {
 483         return ret;
 484     }
 485
 486     if (s->fec_hd && !RTP_PT_IS_RTCP(buf[1])) {
 487         if ((ret_fec = ffurl_write(s->fec_hd, buf, size)) < 0) {
 488             av_log(h, AV_LOG_ERROR, "Failed to send FEC\n");
 489             return ret_fec;
 490         }
 491     }
 492
 493     return ret;
 494 }
 495
 496 static int rtp_close(URLContext *h)
 497 {
 498     RTPContext *s = h->priv_data;
 499
 500     ff_ip_reset_filters(&s->filters);
 501
 502     ffurl_closep(&s->rtp_hd);
 503     ffurl_closep(&s->rtcp_hd);
 504     ffurl_closep(&s->fec_hd);
 505     return 0;
 506 }
 507
 508 /**
 509  * Return the local rtp port used by the RTP connection
 510  * @param h media file context
 511  * @return the local port number
 512  */
 513
 514 int ff_rtp_get_local_rtp_port(URLContext *h)
 515 {
 516     RTPContext *s = h->priv_data;
 517     return ff_udp_get_local_port(s->rtp_hd);
 518 }
 519
 520 /**
 521  * Return the local rtcp port used by the RTP connection
 522  * @param h media file context
 523  * @return the local port number
 524  */
 525
 526 static int rtp_get_file_handle(URLContext *h)
 527 {
 528     RTPContext *s = h->priv_data;
 529     return s->rtp_fd;
 530 }
 531
 532 static int rtp_get_multi_file_handle(URLContext *h, int **handles,
 533                                      int *numhandles)
 534 {
 535     RTPContext *s = h->priv_data;
 536     int *hs       = *handles = av_malloc(sizeof(**handles) * 2);
 537     if (!hs)
 538         return AVERROR(ENOMEM);
 539     hs[0] = s->rtp_fd;
 540     hs[1] = s->rtcp_fd;
 541     *numhandles = 2;
 542     return 0;
 543 }
 544
 545 const URLProtocol ff_rtp_protocol = {
 546     .name                      = "rtp",
 547     .url_open                  = rtp_open,
 548     .url_read                  = rtp_read,
 549     .url_write                 = rtp_write,
 550     .url_close                 = rtp_close,
 551     .url_get_file_handle       = rtp_get_file_handle,
 552     .url_get_multi_file_handle = rtp_get_multi_file_handle,
 553     .priv_data_size            = sizeof(RTPContext),
 554     .flags                     = URL_PROTOCOL_FLAG_NETWORK,
 555     .priv_data_class           = &rtp_class,
 556 };