static int sdp_read_header(AVFormatContext *s)
{
    RTSPState *rt = s->priv_data;
    RTSPStream *rtsp_st;
    int size, i, err;
    char *content;
    char url[1024];

    if (!ff_network_init())
        return AVERROR(EIO);

    if (s->max_delay < 0) /* Not set by the caller */
        s->max_delay = DEFAULT_REORDERING_DELAY;
    if (rt->rtsp_flags & RTSP_FLAG_CUSTOM_IO)
        rt->lower_transport = RTSP_LOWER_TRANSPORT_CUSTOM;

    /* read the whole sdp file */
    /* XXX: better loading */
    content = av_malloc(SDP_MAX_SIZE);
    if (!content)
        return AVERROR(ENOMEM);
    size = avio_read(s->pb, content, SDP_MAX_SIZE - 1);
    if (size <= 0) {
        av_free(content);
        return AVERROR_INVALIDDATA;
    }
    content[size] ='\0';

    err = ff_sdp_parse(s, content);
    av_freep(&content);
    if (err) goto fail;

    /* open each RTP stream */
    for (i = 0; i < rt->nb_rtsp_streams; i++) {
        char namebuf[50];
        rtsp_st = rt->rtsp_streams[i];

        if (!(rt->rtsp_flags & RTSP_FLAG_CUSTOM_IO)) {
            AVDictionary *opts = map_to_opts(rt);

            getnameinfo((struct sockaddr*) &rtsp_st->sdp_ip, sizeof(rtsp_st->sdp_ip),
                        namebuf, sizeof(namebuf), NULL, 0, NI_NUMERICHOST);
            ff_url_join(url, sizeof(url), "rtp", NULL,
                        namebuf, rtsp_st->sdp_port,
                        "?localport=%d&ttl=%d&connect=%d&write_to_source=%d",
                        rtsp_st->sdp_port, rtsp_st->sdp_ttl,
                        rt->rtsp_flags & RTSP_FLAG_FILTER_SRC ? 1 : 0,
                        rt->rtsp_flags & RTSP_FLAG_RTCP_TO_SOURCE ? 1 : 0);

            append_source_addrs(url, sizeof(url), "sources",
                                rtsp_st->nb_include_source_addrs,
                                rtsp_st->include_source_addrs);
            append_source_addrs(url, sizeof(url), "block",
                                rtsp_st->nb_exclude_source_addrs,
                                rtsp_st->exclude_source_addrs);
            err = ffurl_open(&rtsp_st->rtp_handle, url, AVIO_FLAG_READ_WRITE,
                           &s->interrupt_callback, &opts);

            av_dict_free(&opts);

            if (err < 0) {
                err = AVERROR_INVALIDDATA;
                goto fail;
            }
        }
        if ((err = ff_rtsp_open_transport_ctx(s, rtsp_st)))
            goto fail;
    }
    return 0;
fail:
    ff_rtsp_close_streams(s);
    ff_network_close();
    return err;
}