vlc源码分析（一） RTSP会话流程

　　可以先了解一下RTSP/RTP/RTCP的概念与区别：RTP与RTCP协议介绍（转载）。

　　在调试vlc-android时，熟悉了RTSP的会话流程。C表示RTSP客户端,S表示RTSP服务端：

• 第一步：查询服务器端可用方法

1.C->S:OPTIONrequest       //询问S有哪些方法可用

1.S->C:OPTIONresponse    //S回应信息的public头字段中包括提供的所有可用方法

• 第二步：得到媒体描述信息

2.C->S:DESCRIBE request      //要求得到S提供的媒体描述信息

2.S->C:DESCRIBE response    //S回应媒体描述信息，一般是sdp信息

• 第三步：建立RTSP会话

3.C->S:SETUPrequest            //通过Transport头字段列出可接受的传输选项，请求S建立会话

3.S->C:SETUPresponse          //S建立会话，通过Transport头字段返回选择的具体转输选项，并返回建立的Session ID;

• 第四步：请求开始传送数据

4.C->S:PLAY request        //C请求S开始发送数据

4.S->C:PLAYresponse            //S回应该请求的信息

• 第五步： 数据传送播放中

S->C:发送流媒体数据    // 通过RTP协议传送数据

• 第六步：关闭会话，退出

6.C->S:TEARDOWN request      //C请求关闭会话

6.S->C:TEARDOWN response //S回应该请求

　　上述的过程只是标准的、友好的rtsp流程，但实际的需求中并不一定按此过程。其中第三和第四步是必需的！第一步，只要服务器客户端约定好，有哪些方法可用，则option请求可以不要。第二步，如果我们有其他途径得到媒体初始化描述信息（比如http请求等等），则我们也不需要通过rtsp中的describe请求来完成。

　　RTSP服务器默认端口是554，在客户端SETUP的时候会把自身的RTP和RTCP端口告知服务器。在RTSP的session建立后，会使用RTP/RTCP在约定好的端口上传输数据。从调试本地IPC打印的日志可以看出基本的RTSP流程，其中包含了注释，以#开头，建立流程基本是按照上述步骤来的：

#点击播放后，java层打印的信息
V/VLC/PlaybackService: Loading position 0 in [org.videolan.medialibrary.media.MediaWrapper@2fa087e4]
D/VLC: [b48cf028/5d6] core input: Creating an input for 'rtsp://10.3.20.185/onvif-media/media.amp'
D/VLC: [b48cf028/5f5] core input: using timeshift granularity of 50 MiB
D/VLC: [b48cf028/5f5] core input: using default timeshift path
D/VLC: [b48cf028/5f5] core input: `rtsp://admin:admin@10.3.20.185/onvif-media/media.amp?profile=profile_1_h264&sessiontimeout=60&streamtype=unicast' gives access `rtsp' demux `any' path `admin:admin@10.3.20.185/onvif-media/media.amp?profile=profile_1_h264&sessiontimeout=60&streamtype=unicast'
D/VLC: [a095a588/5f5] core input source: creating demux: access='rtsp' demux='any' location='admin:admin@10.3.20.185/onvif-media/media.amp?profile=profile_1_h264&sessiontimeout=60&streamtype=unicast' file='(null)'
D/VLC: [a0829228/5f5] core demux: looking for access_demux module matching "rtsp": 6 candidates
D/VLC: [a0829228/5f5] live555 demux: version 2016.11.28
W/VLC: [a0829228/5f5] core demux: Password in a URI is DEPRECATED
#[vlc-android/vlc/contrib/contrib-android-arm-linux-androideabi/live555/liveMedia/RTSPClient.cpp/connectToServer()]
#使用RTSPClient尝试连接RTSPServer
E/VLC-std: Opening connection to 10.3.20.185, port 554...
#[vlc-android/vlc/contrib/contrib-android-arm-linux-androideabi/live555/liveMedia/RTSPClient.cpp/connectionHandler1()]
#接收到远程的回复
E/VLC-std: ...remote connection opened
#[vlc-android/vlc/contrib/contrib-android-arm-linux-androideabi/live555/liveMedia/RTSPClient.cpp/sendRequest()]
#sendRequest函数打印出来的消息
           Sending request: OPTIONS rtsp://10.3.20.185:554/onvif-media/media.amp?profile=profile_1_h264&sessiontimeout=60&streamtype=unicast RTSP/1.0
           CSeq: 2
           User-Agent: LibVLC/3.0.0-git (LIVE555 Streaming Media v2016.11.28)
I/VLC/BitmapCache: LRUCache size set to 107374182
I/VLC/PlaybackService: Media.Event.MetaChanged: 12
I/VLC/PlaybackService: Media.Event.MetaChanged: 12
#[vlc-android/vlc/contrib/contrib-android-arm-linux-androideabi/live555/liveMedia/RTSPClient.cpp/handleResponseBytes()]
#接收到远程的回复信息
E/VLC-std: Received 143 new bytes of response data.
E/VLC-std: Received a complete OPTIONS response:
           RTSP/1.0  OK
           CSeq:
           #回应信息的public头字段中包括Server提供的所有可用方法
           Public: DESCRIBE, GET_PARAMETER, PAUSE, PLAY, SETUP, SET_PARAMETER, TEARDOWN
           Date: Wed,  Apr  :: GMT
E/VLC-std: Sending request: DESCRIBE rtsp://10.3.20.185:554/onvif-media/media.amp?profile=profile_1_h264&sessiontimeout=60&streamtype=unicast RTSP/1.0
           CSeq: 3
           User-Agent: LibVLC/3.0.0-git (LIVE555 Streaming Media v2016.11.28)
           Accept: application/sdp
E/VLC-std: Received 199 new bytes of response data.
#Server回复需要认证
E/VLC-std: Received a complete DESCRIBE response:
           RTSP/1.0 401 Unauthorized
           CSeq: 3
           WWW-Authenticate: Digest realm="AXIS_WS_ACCC8E41A320", nonce="00058c7aY52967318f73844d686966f513cfdc97f2b1db", stale=FALSE
           Date: Wed, 19 Apr 2017 07:21:53 GMT
E/VLC-std: Resending...
#Client发送认证信息
E/VLC-std: Sending request: DESCRIBE rtsp://10.3.20.185:554/onvif-media/media.amp?profile=profile_1_h264&sessiontimeout=60&streamtype=unicast RTSP/1.0
           CSeq: 4
           Authorization: Digest username="admin", realm="AXIS_WS_ACCC8E41A320", nonce="00058c7aY52967318f73844d686966f513cfdc97f2b1db", uri="rtsp://10.3.20.185:554/onvif-media/media.amp?profile=profile_1_h264&sessiontimeout=60&streamtype=unicast", response="79c25155ce602bdda837ece72c5f5508"
           User-Agent: LibVLC/3.0.0-git (LIVE555 Streaming Media v2016.11.28)
           Accept: application/sdp
E/VLC-std: Received 856 new bytes of response data.
E/VLC-std: Received a complete DESCRIBE response:
           RTSP/1.0 200 OK
           CSeq: 4
           Content-Type: application/sdp
           Content-Base: rtsp://10.3.20.185:554/onvif-media/media.amp/
           Date: Wed, 19 Apr 2017 07:21:55 GMT
           Content-Length: 678

           v=0 #version，SDP协议的version
           o=- 1492586515743424 1492586515743424 IN IP4 10.3.20.185
           s=Media Presentation #session name
           e=NONE #email
           b=AS:50000
           t=0 0
           a=control:rtsp://10.3.20.185:554/onvif-media/media.amp?profile=profile_1_h264&sessiontimeout=60&streamtype=unicast
           a=range:npt=0.000000-
           m=video 0 RTP/AVP 96 #流媒体格式
           c=IN IP4 0.0.0.0 #connect data连接的一些数据
           b=AS:50000
           a=framerate:30.0
           a=transform:1.000000,0.000000,0.000000;0.000000,0.995192,0.000000;0.000000,0.000000,1.000000
           a=control:rtsp://10.3.20.185:554/onvif-media/media.amp/trackID=1?profile=profile_1_h264&sessiontimeout=60&streamtype=unicast
           a=rtpmap:96 H264/90000
           a=fmtp:96 packetization-mode=1; profile-level-id=4D4029; sprop-parameter-sets=Z01AKZpmA8ARPy4C1AQEBBen,aO48gA==
D/VLC: [a0829228/5f5] live555 demux: RTP subsession 'video/H264'
#请求Server建立会话
E/VLC-std: Sending request: SETUP rtsp://10.3.20.185:554/onvif-media/media.amp/trackID=1?profile=profile_1_h264&sessiontimeout=60&streamtype=unicast RTSP/1.0
           CSeq: 5
           Authorization: Digest username="admin", realm="AXIS_WS_ACCC8E41A320", nonce="00058c7aY52967318f73844d686966f513cfdc97f2b1db", uri="rtsp://10.3.20.185:554/onvif-media/media.amp/", response="0f81c42f0f6f9b380e429a0b5adef2ef"
           User-Agent: LibVLC/3.0.0-git (LIVE555 Streaming Media v2016.11.28)
           Transport: RTP/AVP;unicast;client_port=54584-54585 #RTP-RTCP端口号
D/VLC: [b48cf028/5f5] core input: selecting program id=0
D/VLC: [a0829228/5f5] live555 demux: setup start: 0.000000 stop:0.000000
#Server回复会话已建立
E/VLC-std: Received 198 new bytes of response data.
           Received a complete SETUP response:
           RTSP/1.0 200 OK
           CSeq: 5
           Session: CF14A038; timeout=60
           Transport: RTP/AVP;unicast;client_port=54584-54585;server_port=50092-50093;ssrc=534B2131;mode="PLAY"
           Date: Wed, 19 Apr 2017 07:21:56 GMT

#Client请求Server传送数据
           Sending request: PLAY rtsp://10.3.20.185:554/onvif-media/media.amp?profile=profile_1_h264&sessiontimeout=60&streamtype=unicast RTSP/1.0
           CSeq: 6
           Authorization: Digest username="admin", realm="AXIS_WS_ACCC8E41A320", nonce="00058c7aY52967318f73844d686966f513cfdc97f2b1db", uri="rtsp://10.3.20.185:554/onvif-media/media.amp/", response="96a7a81455dad1a9d73958699cbd69a0"
           User-Agent: LibVLC/3.0.0-git (LIVE555 Streaming Media v2016.11.28)
           Session: CF14A038
           Range: npt=0.000-
D/VLC/VideoPlayerActivity: MediaRouter information : android.media.MediaRouter@1a0d4467
I/VLC/VideoPlayerActivity: No secondary display detected
W/MediaRouter: removeCallback(org.videolan.vlc.gui.video.VideoPlayerActivity$1@d47b986): callback not registered
D/VLC/VideoPlayerActivity: Continuing playback from PlaybackService at index 0
E/VLC-std: Received 256 new bytes of response data.
#Server回复数据传送信息
E/VLC-std: Received a complete PLAY response:
           RTSP/1.0 200 OK
           CSeq: 6
           Session: CF14A038
           Range: npt=0-
           RTP-Info: url=rtsp://10.3.20.185:554/onvif-media/media.amp/trackID=1?profile=profile_1_h264&sessiontimeout=60&streamtype=unicast;seq=30405;rtptime=29935497
           Date: Wed, 19 Apr 2017 07:21:57 GMT
D/VLC: [a0829228/5f5] live555 demux: We have a timeout of 60 seconds
D/VLC: [a0829228/5f5] live555 demux: play start: 0.000000 stop:0.000000
D/VLC: [a0829228/5f5] core demux: using access_demux module "live555"
D/VLC: [a0a54228/5f5] core packetizer: looking for packetizer module matching "any": 24 candidates
D/VLC: [a0a54228/5f5] h264 packetizer: found NAL_SPS (sps_id=0)
D/VLC: [a0a54228/5f5] h264 packetizer: found NAL_PPS (pps_id=0 sps_id=0)
D/VLC: [a0a54228/5f5] core packetizer: using packetizer module "h264"
D/VLC: [a0a53ea8/5f5] core decoder: looking for decoder module matching "mediacodec_ndk,all": 41 candidates
W/VideoCapabilities: Unsupported profile 4 for video/avc
W/VideoCapabilities: Unsupported profile 4 for video/avc
W/VideoCapabilities: Unsupported profile 4 for video/avc
......

　

2017.5.7日更新：

　　最近用wireshark抓了下RTSP相关的数据，如下图所示，可以清楚的看到，播放摄像头画面经历了TCP连接建立的3次握手，RTSP会话建立过程和RTP传输数据过程，RTCP数据会每隔一段时间发送一次。

参考资料：

http://blog.csdn.net/leixiaohua1020/article/details/11955341