rtmp推流过程如下：

1）启动connect线程   

static void *connect_thread(void *data)
{
struct rtmp_stream *stream = data;//流信息赋值
int ret;


os_set_thread_name("rtmp-stream: connect_thread");


if (!init_connect(stream)) {//初始化流信息
obs_output_signal_stop(stream->output, OBS_OUTPUT_BAD_PATH);
return NULL;
}


ret = try_connect(stream);//尝试连接


if (ret != OBS_OUTPUT_SUCCESS) {
obs_output_signal_stop(stream->output, ret);//发送停止推流信号
info("Connection to %s failed: %d", stream->path.array, ret);
}


if (!stopping(stream))
pthread_detach(stream->connect_thread);


os_atomic_set_bool(&stream->connecting, false);
return NULL;
}

2）尝试connect   

static int try_connect(struct rtmp_stream *stream)
{
if (dstr_is_empty(&stream->path)) {//推流地址不能为空
warn("URL is empty");
return OBS_OUTPUT_BAD_PATH;
}


info("Connecting to RTMP URL %s...", stream->path.array);


memset(&stream->rtmp.Link, 0, sizeof(stream->rtmp.Link));
if (!RTMP_SetupURL(&stream->rtmp, stream->path.array))
return OBS_OUTPUT_BAD_PATH;


RTMP_EnableWrite(&stream->rtmp);//写权限


dstr_copy(&stream->encoder_name, "FMLE/3.0 (compatible; obs-studio/");


#ifdef HAVE_OBSCONFIG_H
dstr_cat(&stream->encoder_name, OBS_VERSION);
#else
dstr_catf(&stream->encoder_name, "%d.%d.%d",
LIBOBS_API_MAJOR_VER,
LIBOBS_API_MINOR_VER,
LIBOBS_API_PATCH_VER);
#endif


dstr_cat(&stream->encoder_name, "; FMSc/1.0)");


set_rtmp_dstr(&stream->rtmp.Link.pubUser,   &stream->username);
set_rtmp_dstr(&stream->rtmp.Link.pubPasswd, &stream->password);
set_rtmp_dstr(&stream->rtmp.Link.flashVer,  &stream->encoder_name);
stream->rtmp.Link.swfUrl = stream->rtmp.Link.tcUrl;


RTMP_AddStream(&stream->rtmp, stream->key.array);//key连接


for (size_t idx = 1;; idx++) {
obs_encoder_t *encoder = obs_output_get_audio_encoder(
stream->output, idx);
const char *encoder_name;


if (!encoder)
break;


encoder_name = obs_encoder_get_name(encoder);
RTMP_AddStream(&stream->rtmp, encoder_name);//编码器
}


stream->rtmp.m_outChunkSize       = 4096;
stream->rtmp.m_bSendChunkSizeInfo = true;
stream->rtmp.m_bUseNagle          = true;


#ifdef _WIN32
win32_log_interface_type(stream);
#endif


if (!RTMP_Connect(&stream->rtmp, NULL))//推流服务器连接
return OBS_OUTPUT_CONNECT_FAILED;
if (!RTMP_ConnectStream(&stream->rtmp, 0))//流连接
return OBS_OUTPUT_INVALID_STREAM;


info("Connection to %s successful", stream->path.array);


return init_send(stream);//推流线程
}

3) connect过程 
int
RTMP_Connect(RTMP *r, RTMPPacket *cp)
{
#ifdef _WIN32
    HOSTENT *h;
#endif
    struct sockaddr_storage service;
    socklen_t addrlen = 0;
    if (!r->Link.hostname.av_len)
        return FALSE;


#ifdef _WIN32
    //COMODO security software sandbox blocks all DNS by returning "host not found"
    h = gethostbyname("localhost");
    if (!h && GetLastError() == WSAHOST_NOT_FOUND)
    {
        RTMP_Log(RTMP_LOGERROR, "RTMP_Connect: Connection test failed. This error is likely caused by Comodo Internet Security running OBS in sandbox mode. Please add OBS to the Comodo automatic sandbox exclusion list, restart OBS and try again (11001).");
        return FALSE;
    }
#endif


    memset(&service, 0, sizeof(service));


    if (r->Link.socksport)
    {
        /* Connect via SOCKS */
        if (!add_addr_info(&service, &addrlen, &r->Link.sockshost, r->Link.socksport))
            return FALSE;
    }
    else
    {
        /* Connect directly */
        if (!add_addr_info(&service, &addrlen, &r->Link.hostname, r->Link.port))
            return FALSE;
    }


    if (!RTMP_Connect0(r, (struct sockaddr *)&service, addrlen))
        return FALSE;


    r->m_bSendCounter = TRUE;


    return RTMP_Connect1(r, cp);
}

RTMP_Connect0(RTMP *r, struct sockaddr * service, socklen_t addrlen)

RTMP_Connect1(RTMP *r, RTMPPacket *cp)

4）三次握手

static int
HandShake(RTMP *r, int FP9HandShake)