RTSP簡介
RTSP(Real Time Streaming Protocol)是由Real Network和Netscape共同提出的如何有效地在IP網(wǎng)絡上傳輸流媒體數(shù)據(jù)的應用層協(xié)議环壤。RTSP對流媒體提供了諸如暫停答朋,快進等控制谤辜,而它本身并不傳輸數(shù)據(jù),RTSP的作用相當于流媒體服務器的遠程控制薄扁。服務器端可以自行選擇使用TCP或UDP來傳送串流內(nèi)容,它的語法和運作跟HTTP 1.1類似,但并不特別強調(diào)時間同步,所以比較能容忍網(wǎng)絡延遲白翻。
RTSP和HTTP RTP(RTCP)的關(guān)系
RTSP和HTTP
- 聯(lián)系:兩者都用純文本來發(fā)送消息,且rtsp協(xié)議的語法也和HTTP類似绢片。Rtsp一開始這樣設計滤馍,也是為了能夠兼容使用以前寫的HTTP協(xié)議分析代碼 。
- 區(qū)別:rtsp是有狀態(tài)的杉畜,不同的是RTSP的命令需要知道現(xiàn)在正處于一個什么狀態(tài),也就是說rtsp的命令總是按照順序來發(fā)送衷恭,某個命令總在另外一個命令之前要發(fā)送此叠。Rtsp不管處于什么狀態(tài)都不會斷掉連接。而http則不保存狀態(tài)随珠,協(xié)議在發(fā)送一個命令以后灭袁,連接就會斷開,且命令之間是沒有依賴性窗看。rtsp協(xié)議使用554端口茸歧,http使用80端口。
RTSP和RTP(RTCP)
-
RTP:Realtime Transport Potocol 實時傳輸協(xié)議
RTP提供時間標志,序列號以及其他能夠保證在實時數(shù)據(jù)傳輸時處理時間的方法显沈。 -
RTCP:Realtime Transport Control Potocol 實時傳輸控制協(xié)議
RTCP是RTP的控制部分,用來保證服務質(zhì)量和成員管理软瞎。RTP和RTCP是一起使用的。 -
RTSP:RealTime Streaming Potocol 實時流協(xié)議
RTSP具體數(shù)據(jù)傳輸交給RTP,提供對流的遠程控制
RTP是基于 UDP協(xié)議的拉讯, UDP不用建立連接涤浇,效率更高;但允許丟包魔慷, 這就要求在重新組裝媒體的時候多做些工作
RTP只是包裹內(nèi)容信息只锭,而RTCP是交換控制信息的,Qos是通過RTCP實現(xiàn)的
應用程序?qū)氖莗lay, seek, pause, stop等命令院尔,RTSP則是處理這些命令蜻展,在UDP傳輸時并使用RTP(RTCP)來完成。如果是TCP連接則不會使用RTP(RTCP)邀摆。
RTSP的client連接server通過SDP(會話描述協(xié)議)傳遞信息纵顾,詳細請見:RTSP消息
RTSP消息
RTSP的消息有兩大類,一是請求消息(request)栋盹,一是回應消息(response)片挂,兩種消息的格式不同。
請求消息格式:
方法 URI RTSP版本 CR LF
消息頭 CR LF CR LF
消息體 CR LF
方法包括:OPTIONS、SETUP音念、PLAY沪饺、TEARDOWN DESCRIBE
URI是接收方(服務端)的地址,例如:rtsp://192.168.22.136:5000/v0
每行后面的CR LF表示回車換行闷愤,需要接收端有相應的解析整葡,消息頭需要有兩個CR LF。
DESCRIBE rtsp://192.168.1.211 RTSP/1.0
CSeq: 1
Accept: application/sdp
User-Agent: magnus-fc
回應消息格式:
RTSP版本 狀態(tài)碼 解釋 CR LF
消息頭 CR LF CR LF
消息體 CR LF
其中RTSP版本一般都是RTSP/1.0讥脐,狀態(tài)碼是一個數(shù)值遭居,200表示成功,解釋是與狀態(tài)碼對應的文本解釋旬渠,詳細請見:SDP協(xié)議介紹俱萍。
RTSP/1.0 200 OK
CSeq: 1
Server: GrandStream Rtsp Server V100R001
Content-Type: application/sdp
Content-length: 256
Content-Base: rtsp://192.168.1.211/0
v=0
o=StreamingServer 3331435948 1116907222000 IN IP4 192.168.1.211
s=h264.mp4
c=IN IP4 0.0.0.0
t=0 0
a=control:*
m=video 0 RTP/AVP 96
a=control:trackID=0
a=rtpmap:96 H264/90000
m=audio 0 RTP/AVP 97
a=control:trackID=1
a=rtpmap:97 G726-16/8000
簡單的rtsp交互過程:
C表示rtsp客戶端, S表示rtsp服務端
step1:
C->S:OPTION request //詢問S有哪些方法可用
S->C:OPTION response //S回應信息中包括提供的所有可用方法
step2:
C->S:DESCRIBE request //要求得到S提供的媒體初始化描述信息
S->C:DESCRIBE response //S回應媒體初始化描述信息,主要是sdp
step3:
C->S:SETUP request //設置會話的屬性告丢,以及傳輸模式枪蘑,提醒S建立會話
S->C:SETUP response //S建立會話,返回會話標識符岖免,以及會話相關(guān)信息
step4:
C->S:PLAY request //C請求播放
S->C:PLAY response //S回應該請求的信息
S->C:發(fā)送流媒體數(shù)據(jù)
step5:
C->S:TEARDOWN request //C請求關(guān)閉會話
S->C:TEARDOWN response //S回應該請求
RTSP中常用方法
OPTION
得到服務器提供的可用方法
OPTIONS rtsp://192.168.20.136:5000/xxx666 RTSP/1.0
CSeq: 1 //每個消息都有序號來標記岳颇,第一個包通常是option請求消息
User-Agent: VLC media player (LIVE555 Streaming Media v2005.11.10)
服務器的回應信息包括提供的一些方法,例如:
RTSP/1.0 200 OK
Server: UServer 0.9.7_rc1
Cseq: 1 //每個回應消息的cseq數(shù)值和請求消息的cseq相對應
Public: OPTIONS, DESCRIBE, SETUP, TEARDOWN, PLAY, PAUSE, SCALE,GET_PARAMETER //服務器提供的可用的方法
DESCRIBE
C向S發(fā)起DESCRIBE請求,為了得到會話描述信息(SDP):
DESCRIBE rtsp://192.168.20.136:5000/xxx666 RTSP/1.0
CSeq: 2
token:
Accept: application/sdp
User-Agent: VLC media player (LIVE555 Streaming Media v2005.11.10)
服務器回應一些對此會話的描述信息(sdp):
RTSP/1.0 200 OK
Server: UServer 0.9.7_rc1
Cseq: 2
x-prev-url: rtsp://192.168.20.136:5000
x-next-url: rtsp://192.168.20.136:5000
x-Accept-Retransmit: our-retransmit
x-Accept-Dynamic-Rate: 1
Cache-Control: must-revalidate
Last-Modified: Fri, 10 Nov 2006 12:34:38 GMT
Date: Fri, 10 Nov 2006 12:34:38 GMT
Expires: Fri, 10 Nov 2006 12:34:38 GMT
Content-Base: rtsp://192.168.20.136:5000/xxx666/
Content-Length: 344
Content-Type: application/sdp
v=0 //以下都是sdp信息
o=OnewaveUServerNG 1451516402 1025358037 IN IP4 192.168.20.136
s=/xxx666
u=http:///
e=admin@
c=IN IP4 0.0.0.0
t=0 0
a=isma-compliance:1,1.0,1
a=range:npt=0-
m=video 0 RTP/AVP 96 //m表示媒體描述,下面是對會話中視頻通道的媒體描述
a=rtpmap:96 MP4V-ES/90000
a=fmtp:96 profile-level-id=245;config=000001B0F5000001B509000001000000012000C888B0E0E0FA62D089028307 a=control:trackID=0 //trackID=0表示視頻流用的是通道0
SETUP
客戶端提醒服務器建立會話,并確定傳輸模式:
SETUP rtsp://192.168.20.136:5000/xxx666/trackID=0 RTSP/1.0
CSeq: 3
Transport: RTP/AVP/TCP;unicast;interleaved=0-1
User-Agent: VLC media player (LIVE555 Streaming Media v2005.11.10)
//uri中 帶有trackID=0颅湘,表示對該通道進行設置话侧。Transport參數(shù)設置了傳輸模式,包的結(jié)構(gòu)闯参。接下來的數(shù)據(jù)包頭部第二個字節(jié)位置就是 interleaved瞻鹏,它的值是每個通道都不同的,trackID=0的interleaved值有兩個0或1鹿寨,0表示rtp包乙漓,1表示rtcp包,接收端根據(jù)interleaved的值來區(qū)別是哪種數(shù)據(jù)包释移。
服務器回應信息:
RTSP/1.0 200 OK
Server: UServer 0.9.7_rc1
Cseq: 3
Session: 6310936469860791894 //服務器回應的會話標識符
Cache-Control: no-cache
Transport: RTP/AVP/TCP;unicast;interleaved=0-1;ssrc=6B8B4567
PLAY
客戶端發(fā)送播放請求:
PLAY rtsp://192.168.20.136:5000/xxx666 RTSP/1.0
CSeq: 4
Session: 6310936469860791894
Range: npt=0.000- //設置播放時間的范圍
User-Agent: VLC media player (LIVE555 Streaming Media v2005.11.10)
服務器回應信息:
RTSP/1.0 200 OK
Server: UServer 0.9.7_rc1
Cseq: 4
Session: 6310936469860791894
Range: npt=0.000000-
RTP-Info: url=trackID=0;seq=17040;rtptime=1467265309
//seq和rtptime都是rtp包中的信息
TEARDOWN
客戶端發(fā)起關(guān)閉請求:
TEARDOWN rtsp://192.168.20.136:5000/xxx666 RTSP/1.0
CSeq: 5
Session: 6310936469860791894
User-Agent: VLC media player (LIVE555 Streaming Media v2005.11.10)
服務器回應:
RTSP/1.0 200 OK
Server: UServer 0.9.7_rc1
Cseq: 5
Session: 6310936469860791894
SDP協(xié)議
sdp的格式:
v=<version>
o=<username> <session id> <version> <network type> <address type> <address>
s=<session name>
i=<session description>
u=<URI>
e=<email address>
p=<phone number>
c=<network type> <address type> <connection address>
b=<modifier>:<bandwidth-value>
t=<start time> <stop time>
r=<repeat interval> <active duration> <list of offsets from start-time>
z=<adjustment time> <offset> <adjustment time> <offset> ....
k=<method>
k=<method>:<encryption key>
a=<attribute>
a=<attribute>:<value>
m=<media> <port> <transport> <fmt list>
v = (協(xié)議版本)
o = (所有者/創(chuàng)建者和會話標識符)
s = (會話名稱)
i = * (會話信息)
u = * (URI 描述)
e = * (Email 地址)
p = * (電話號碼)
c = * (連接信息)
b = * (帶寬信息)
z = * (時間區(qū)域調(diào)整)
k = * (加密密鑰)
a = * (0 個或多個會話屬性行)
時間描述:
t = (會話活動時間)
r = * (0或多次重復次數(shù))媒體描述:
m = (媒體名稱和傳輸?shù)刂罚?br> i = * (媒體標題)
c = * (連接信息 — 如果包含在會話層則該字段可選)
b = * (帶寬信息)
k = * (加密密鑰)
a = * (0 個或多個媒體屬性行)
SDP一會話描述協(xié)議一描述SAP叭披、SIP和RTSR會話的協(xié)議,是一種文件描述協(xié)議,是由服務器生成的描述媒體文件編碼信息以及所在服務器的鏈接等的信息。在多媒體會話 中sDP傳送有關(guān)媒體流的信息,使會話描述的參人方加人會話玩讳。SDP主要用于Intemet網(wǎng)中,但也可以在其它網(wǎng)絡環(huán)境下使用涩蜘。SDP十分通用,可描述其它網(wǎng)絡環(huán)境中的會話,但主要用 于Intemet中。在Intemet環(huán)境下,SDP有兩個主要目的:一是表明會話存在,二是傳送足夠信息給接收方,以便能加人熏纯、參加該會話同诫。SDP所傳達的信息包括:會話名稱和目的,會話 活動時間,組成會話媒體種類,接收這些媒體的控制信息(如地址、端口樟澜、格式误窖、帶寬和會議管理人員資料等)叮盘。
總結(jié):在RTSP交互過程中,只要在客戶端發(fā)出Describe請求的時候霹俺,服務端回應的時候會有SDP消息發(fā)出柔吼,用SDP來描述會話情況和內(nèi)容,方便客戶端能夠加入該會話丙唧。
RTSP基于libcurl代碼實現(xiàn)
/*
* Copyright (c) 2011, Jim Hollinger
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* * Neither the name of Jim Hollinger nor the names of its contributors
* may be used to endorse or promote products derived from this
* software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
*/
/* <DESC>
* A basic RTSP transfer
* </DESC>
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <curl/curl.h>
#if defined (WIN32)
#include <conio.h> /* _getch() */
#else
#include <termios.h>
#include <unistd.h>
#define VERSION_STR "V1.0"
/* error handling macros */
#define my_curl_easy_setopt(A, B, C) \
res = curl_easy_setopt((A), (B), (C)); \
if(!res) \
fprintf(stderr, "curl_easy_setopt(%s, %s, %s) failed: %d\n", \
#A, #B, #C, res);
#define my_curl_easy_perform(A) \
res = curl_easy_perform(A); \
if(!res) \
fprintf(stderr, "curl_easy_perform(%s) failed: %d\n", #A, res);
static int _getch(void)
{
struct termios oldt, newt;
int ch;
tcgetattr(STDIN_FILENO, &oldt);
newt = oldt;
newt.c_lflag &= ~( ICANON | ECHO);
tcsetattr(STDIN_FILENO, TCSANOW, &newt);
ch = getchar();
tcsetattr(STDIN_FILENO, TCSANOW, &oldt);
return ch;
}
#endif
/* send RTSP OPTIONS request */
static void rtsp_options(CURL *curl, const char *uri)
{
CURLcode res = CURLE_OK;
printf("\nRTSP: OPTIONS %s\n", uri);
my_curl_easy_setopt(curl, CURLOPT_RTSP_STREAM_URI, uri);
my_curl_easy_setopt(curl, CURLOPT_RTSP_REQUEST, (long)CURL_RTSPREQ_OPTIONS);
my_curl_easy_perform(curl);
}
/* send RTSP DESCRIBE request and write sdp response to a file */
static void rtsp_describe(CURL *curl, const char *uri,
const char *sdp_filename)
{
CURLcode res = CURLE_OK;
FILE *sdp_fp = fopen(sdp_filename, "wb");
printf("\nRTSP: DESCRIBE %s\n", uri);
if(sdp_fp == NULL) {
fprintf(stderr, "Could not open '%s' for writing\n", sdp_filename);
sdp_fp = stdout;
}
else {
printf("Writing SDP to '%s'\n", sdp_filename);
}
my_curl_easy_setopt(curl, CURLOPT_WRITEDATA, sdp_fp);
my_curl_easy_setopt(curl, CURLOPT_RTSP_REQUEST, (long)CURL_RTSPREQ_DESCRIBE);
my_curl_easy_perform(curl);
my_curl_easy_setopt(curl, CURLOPT_WRITEDATA, stdout);
if(sdp_fp != stdout) {
fclose(sdp_fp);
}
}
/* send RTSP SETUP request */
static void rtsp_setup(CURL *curl, const char *uri, const char *transport)
{
CURLcode res = CURLE_OK;
printf("\nRTSP: SETUP %s\n", uri);
printf(" TRANSPORT %s\n", transport);
my_curl_easy_setopt(curl, CURLOPT_RTSP_STREAM_URI, uri);
my_curl_easy_setopt(curl, CURLOPT_RTSP_TRANSPORT, transport);
my_curl_easy_setopt(curl, CURLOPT_RTSP_REQUEST, (long)CURL_RTSPREQ_SETUP);
my_curl_easy_perform(curl);
}
/* send RTSP PLAY request */
static void rtsp_play(CURL *curl, const char *uri, const char *range)
{
CURLcode res = CURLE_OK;
printf("\nRTSP: PLAY %s\n", uri);
my_curl_easy_setopt(curl, CURLOPT_RTSP_STREAM_URI, uri);
my_curl_easy_setopt(curl, CURLOPT_RANGE, range);
my_curl_easy_setopt(curl, CURLOPT_RTSP_REQUEST, (long)CURL_RTSPREQ_PLAY);
my_curl_easy_perform(curl);
}
/* send RTSP TEARDOWN request */
static void rtsp_teardown(CURL *curl, const char *uri)
{
CURLcode res = CURLE_OK;
printf("\nRTSP: TEARDOWN %s\n", uri);
my_curl_easy_setopt(curl, CURLOPT_RTSP_REQUEST, (long)CURL_RTSPREQ_TEARDOWN);
my_curl_easy_perform(curl);
}
/* convert url into an sdp filename */
static void get_sdp_filename(const char *url, char *sdp_filename,
size_t namelen)
{
const char *s = strrchr(url, '/');
strcpy(sdp_filename, "video.sdp");
if(s != NULL) {
s++;
if(s[0] != '\0') {
snprintf(sdp_filename, namelen, "%s.sdp", s);
}
}
}
/* scan sdp file for media control attribute */
static void get_media_control_attribute(const char *sdp_filename,
char *control)
{
int max_len = 256;
char *s = malloc(max_len);
FILE *sdp_fp = fopen(sdp_filename, "rb");
control[0] = '\0';
if(sdp_fp != NULL) {
while(fgets(s, max_len - 2, sdp_fp) != NULL) {
sscanf(s, " a = control: %s", control);
}
fclose(sdp_fp);
}
free(s);
}
/* main app */
int main(int argc, char * const argv[])
{
#if 1
const char *transport = "RTP/AVP;unicast;client_port=1234-1235"; /* UDP */
#else
/* TCP */
const char *transport = "RTP/AVP/TCP;unicast;client_port=1234-1235";
#endif
const char *range = "0.000-";
int rc = EXIT_SUCCESS;
char *base_name = NULL;
printf("\nRTSP request %s\n", VERSION_STR);
printf(" Project web site: http://code.google.com/p/rtsprequest/\n");
printf(" Requires curl V7.20 or greater\n\n");
/* check command line */
if((argc != 2) && (argc != 3)) {
base_name = strrchr(argv[0], '/');
if(base_name == NULL) {
base_name = strrchr(argv[0], '\\');
}
if(base_name == NULL) {
base_name = argv[0];
}
else {
base_name++;
}
printf("Usage: %s url [transport]\n", base_name);
printf(" url of video server\n");
printf(" transport (optional) specifier for media stream"
" protocol\n");
printf(" default transport: %s\n", transport);
printf("Example: %s rtsp://192.168.0.2/media/video1\n\n", base_name);
rc = EXIT_FAILURE;
}
else {
const char *url = argv[1];
char *uri = malloc(strlen(url) + 32);
char *sdp_filename = malloc(strlen(url) + 32);
char *control = malloc(strlen(url) + 32);
CURLcode res;
get_sdp_filename(url, sdp_filename, strlen(url) + 32);
if(argc == 3) {
transport = argv[2];
}
/* initialize curl */
res = curl_global_init(CURL_GLOBAL_ALL);
if(res == CURLE_OK) {
curl_version_info_data *data = curl_version_info(CURLVERSION_NOW);
CURL *curl;
fprintf(stderr, " curl V%s loaded\n", data->version);
/* initialize this curl session */
curl = curl_easy_init();
if(curl != NULL) {
my_curl_easy_setopt(curl, CURLOPT_VERBOSE, 0L);
my_curl_easy_setopt(curl, CURLOPT_NOPROGRESS, 1L);
my_curl_easy_setopt(curl, CURLOPT_HEADERDATA, stdout);
my_curl_easy_setopt(curl, CURLOPT_URL, url);
/* request server options */
snprintf(uri, strlen(url) + 32, "%s", url);
rtsp_options(curl, uri);
/* request session description and write response to sdp file */
rtsp_describe(curl, uri, sdp_filename);
/* get media control attribute from sdp file */
get_media_control_attribute(sdp_filename, control);
/* setup media stream */
snprintf(uri, strlen(url) + 32, "%s/%s", url, control);
rtsp_setup(curl, uri, transport);
/* start playing media stream */
snprintf(uri, strlen(url) + 32, "%s/", url);
rtsp_play(curl, uri, range);
printf("Playing video, press any key to stop ...");
_getch();
printf("\n");
/* teardown session */
rtsp_teardown(curl, uri);
/* cleanup */
curl_easy_cleanup(curl);
curl = NULL;
}
else {
fprintf(stderr, "curl_easy_init() failed\n");
}
curl_global_cleanup();
}
else {
fprintf(stderr, "curl_global_init(%s) failed: %d\n",
"CURL_GLOBAL_ALL", res);
}
free(control);
free(sdp_filename);
free(uri);
}
return rc;
}