vlc源碼分析（一） RTSP會話流程

　　可以先了解一下RTSP/RTP/RTCP的概念與區別：RTP與RTCP協議介紹（轉載）。

　　在調試vlc-android時，熟悉了RTSP的會話流程。C表示RTSP客戶端,S表示RTSP服務端：

• 第一步：查詢服務器端可用方法

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

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

• 第二步：得到媒體描述信息

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

2.S->C:DESCRIBE response    //S回應媒體描述信息，一般是sdp信息

• 第三步：建立RTSP會話

3.C->S:SETUPrequest            //通過Transport頭字段列出可接受的傳輸選項，請求S建立會話

3.S->C:SETUPresponse          //S建立會話，通過Transport頭字段返回選擇的具體轉輸選項，並返回建立的Session ID;

• 第四步：請求開始傳送數據

4.C->S:PLAY request        //C請求S開始發送數據

4.S->C:PLAYresponse            //S回應該請求的信息

•  第五步： 數據傳送播放中

S->C:發送流媒體數據    // 通過RTP協議傳送數據

• 第六步：關閉會話，退出

6.C->S:TEARDOWN request      //C請求關閉會話

6.S->C:TEARDOWN response //S回應該請求

　　上述的過程只是標准的、友好的rtsp流程，但實際的需求中並不一定按此過程。其中第三和第四步是必需的！第一步，只要服務器客戶端約定好，有哪些方法可用，則option請求可以不要。第二步，如果我們有其他途徑得到媒體初始化描述信息（比如http請求等等），則我們也不需要通過rtsp中的describe請求來完成。

　　RTSP服務器默認端口是554，在客戶端SETUP的時候會把自身的RTP和RTCP端口告知服務器。在RTSP的session建立后，會使用RTP/RTCP在約定好的端口上傳輸數據。從調試本地IPC打印的日志可以看出基本的RTSP流程，其中包含了注釋，以#開頭，建立流程基本是按照上述步驟來的：

#點擊播放后，java層打印的信息
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嘗試連接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()]
#接收到遠程的回復
E/VLC-std: ...remote connection opened
#[vlc-android/vlc/contrib/contrib-android-arm-linux-androideabi/live555/liveMedia/RTSPClient.cpp/sendRequest()]
#sendRequest函數打印出來的消息
           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()]
#接收到遠程的回復信息
E/VLC-std: Received 143 new bytes of response data.
E/VLC-std: Received a complete OPTIONS response:
           RTSP/1.0 200 OK
           CSeq: 2
           #回應信息的public頭字段中包括Server提供的所有可用方法
           Public: DESCRIBE, GET_PARAMETER, PAUSE, PLAY, SETUP, SET_PARAMETER, TEARDOWN
           Date: Wed, 19 Apr 2017 07:21:53 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回復需要認證
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發送認證信息
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協議的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 #流媒體格式
           c=IN IP4 0.0.0.0 #connect data連接的一些數據
           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'
#請求Server建立會話
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端口號
D/VLC: [b48cf028/5f5] core input: selecting program id=0
D/VLC: [a0829228/5f5] live555 demux: setup start: 0.000000 stop:0.000000
#Server回復會話已建立
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請求Server傳送數據
           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回復數據傳送信息
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相關的數據，如下圖所示，可以清楚的看到，播放攝像頭畫面經歷了TCP連接建立的3次握手，RTSP會話建立過程和RTP傳輸數據過程，RTCP數據會每隔一段時間發送一次。

參考資料：

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