2024/09/30

RTSP

RTSP是1996年由 RealNetworks, Netscape, 哥倫比亞大學開發,提交草案給 IETF,1998年發布為 RFC2326,2016年RTSP 2.0 發布於 RFC 7826。RTSP 是串流媒體伺服器的控制協定,可建立與控制終端設備跟伺服器之間的多媒體 session。

RTSP 協定本身看起來跟 HTTP 類似,但 HTTP 本身是 stateless,而RTSP 是 stateful,故需要追蹤 session。RTSP 是用 TCP 連線,而多媒體本身,是用 RTP 傳輸,可以用 TCP 或 UDP,常見狀況是為求傳輸速度快,使用 UDP。

節錄一個 RTSP client 取得 RTSP 的封包過程

  1. Options

    查詢 RTSP server 支援的 command

    Client -> Server

    Request: OPTIONS rtsp://192.168.1.11:8554/mystream RTSP/1.0\r\n
    CSeq: 2\r\n
    User-Agent: LibVLC/3.0.20 (LIVE555 Streaming Media v2016.11.28)\r\n
    \r\n

    Server -> Client

    Response: RTSP/1.0 200 OK\r\n
    CSeq: 2\r\n
    Public: DESCRIBE, ANNOUNCE, SETUP, PLAY, RECORD, PAUSE, GET_PARAMETER, TEARDOWN\r\n
    Server: gortsplib\r\n
    \r\n
  2. Describe

    查詢可處理的多媒體資料格式,server 以 SDP 方式回覆

    Client -> Server

    Request: DESCRIBE rtsp://192.168.1.11:8554/mystream RTSP/1.0\r\n
    CSeq: 3\r\n
    User-Agent: LibVLC/3.0.20 (LIVE555 Streaming Media v2016.11.28)\r\n
    Accept: application/sdp\r\n
    \r\n

    Server -> Client

    Response: RTSP/1.0 200 OK\r\n
    CSeq: 3\r\n
    Content-Base: rtsp://192.168.1.11:8554/mystream/\r\n
    Content-length: 560
    Content-type: application/sdp
    Server: gortsplib\r\n
    \r\n
    Session Description Protocol Version (v): 0
    Owner/Creator, Session Id (o): - 0 0 IN IP4 127.0.0.1
    Session Name (s): test
    Connection Information (c): IN IP4 0.0.0.0
    Time Description, active time (t): 0 0
    Media Description, name and address (m): video 0 RTP/AVP 96
    Media Attribute (a): control:rtsp://192.168.1.11:8554/mystream/trackID=0
    Media Attribute (a): rtpmap:96 H264/90000
    Media Attribute (a): fmtp:96 packetization-mode=1; profile-level-id=640032; sprop-parameter-sets=Z2QAMqzIUB4AiflwEQAAAwPpAAC7gA8YMZY=,aOk4XLIs
    Media Description, name and address (m): audio 0 RTP/AVP 97
    Media Attribute (a): control:rtsp://192.168.1.11:8554/mystream/trackID=1
    Media Attribute (a): rtpmap:97 mpeg4-generic/48000/2
    Media Attribute (a): fmtp:97 config=1190; indexdeltalength=3; indexlength=3; mode=AAC-hbr; profile-level-id=1; sizelength=13; streamtype=5
  3. Setup

    要求 server 設定傳送某一個 media stream,setup 要在 play 之前完成

    Client -> Server

    Request: SETUP rtsp://192.168.1.11:8554/mystream/trackID=0 RTSP/1.0\r\n
    CSeq: 4\r\n
    User-Agent: LibVLC/3.0.20 (LIVE555 Streaming Media v2016.11.28)\r\n
    Transport: RTP/AVP/TCP;unicast;interleaved=0-1
    \r\n

    Server -> Client

    Response: RTSP/1.0 200 OK\r\n
    CSeq: 4\r\n
    Server: gortsplib\r\n
    Session: 262553a7d5084e8fb57f9d8f485c89f4
    Transport: RTP/AVP/TCP;unicast;interleaved=0-1;ssrc=03DAD41B
    \r\n
  4. Setup

    client 透過 setup 跟 server 確認 stream session

    Client -> Server

    Request: SETUP rtsp://192.168.1.11:8554/mystream/trackID=1 RTSP/1.0\r\n
    CSeq: 5\r\n
    User-Agent: LibVLC/3.0.20 (LIVE555 Streaming Media v2016.11.28)\r\n
    Transport: RTP/AVP/TCP;unicast;interleaved=2-3
    Session: 262553a7d5084e8fb57f9d8f485c89f4
    \r\n

    Server -> Client

    Response: RTSP/1.0 200 OK\r\n
    CSeq: 5\r\n
    Server: gortsplib\r\n
    Session: 262553a7d5084e8fb57f9d8f485c89f4
    Transport: RTP/AVP/TCP;unicast;interleaved=2-3;ssrc=294122AE
    \r\n
  5. Play

    在 setup 設定的 session 裡面,開始播放 media

    Client -> Server

    Request: PLAY rtsp://192.168.1.11:8554/mystream/ RTSP/1.0\r\n
    CSeq: 6\r\n
    User-Agent: LibVLC/3.0.20 (LIVE555 Streaming Media v2016.11.28)\r\n
    Session: 262553a7d5084e8fb57f9d8f485c89f4
    Range: npt=0.000-\r\n
    \r\n

    Server -> Client

    Response: RTSP/1.0 200 OK\r\n
    CSeq: 6\r\n
    RTP-Info: url=rtsp://192.168.1.11:8554/mystream/trackID=0;seq=10453;rtptime=1024864644,url=rtsp://192.168.1.11:8554/mystream/trackID=1;seq=4824;rtptime=3779844790\r\n
    Server: gortsplib\r\n
    Session: 262553a7d5084e8fb57f9d8f485c89f4
    \r\n
  6. RTP

    用 RTP 的格式,傳送 media 內容

    Server -> Client

    10.. .... = Version: RFC 1889 Version (2)
    ..0. .... = Padding: False
    ...0 .... = Extension: False
    .... 0000 = Contributing source identifiers count: 0
    0... .... = Marker: False
    Payload type: DynamicRTP-Type-96 (96)
    Sequence number: 10453
    Timestamp: 1024871144
    Synchronization Source identifier: 0x03dad41b (64672795)
    Payload: 09f0
  7. Teardown

    client 通知 server 停止播放 media

    Client -> Server

    Request: TEARDOWN rtsp://192.168.1.11:8554/mystream/ RTSP/1.0\r\n
    CSeq: 7\r\n
    User-Agent: LibVLC/3.0.20 (LIVE555 Streaming Media v2016.11.28)\r\n
    Session: 262553a7d5084e8fb57f9d8f485c89f4
    \r\n

References

即時串流協定 - 維基百科,自由的百科全書

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