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Original commit message from CVS: * gst/rtsp/README: * gst/rtsp/gstrtspsrc.c: (gst_rtsp_proto_get_type), (gst_rtspsrc_class_init), (gst_rtspsrc_create_stream), (gst_rtspsrc_add_element), (gst_rtspsrc_set_state), (gst_rtspsrc_stream_setup_rtp), (gst_rtspsrc_stream_configure_transport), (find_stream), (gst_rtspsrc_loop), (gst_rtspsrc_open), (gst_rtspsrc_play), (gst_rtspsrc_change_state): * gst/rtsp/rtsptransport.c: (rtsp_transport_new), (rtsp_transport_init), (parse_mode), (parse_range), (rtsp_transport_parse), (rtsp_transport_free): RTSP cleanups.
156 lines
5.4 KiB
Text
156 lines
5.4 KiB
Text
RTSP source
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-----------
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The RTSP source establishes a connection to an RTSP server and sets up
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the UDP sources and RTP session handlers.
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An RTSP session is created as follows:
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- Parse RTSP URL:
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ex:
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rtsp://thread:5454/south-rtsp.mp3
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- Open a connection to the server with the url. All further conversation with
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the server should be done with this connection. Each request/reply has
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a CSeq number added to the header.
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- Send a DESCRIBE request for the url. We currently support a response in
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SDP.
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ex:
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>> DESCRIBE rtsp://thread:5454/south-rtsp.mp3 RTSP/1.0
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>> Accept: application/sdp
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>> CSeq: 0
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>>
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<< RTSP/1.0 200 OK
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<< Content-Length: 84
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<< Content-Type: application/sdp
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<< CSeq: 0
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<< Date: Wed May 11 13:09:37 2005 GMT
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<<
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<< v=0
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<< o=- 0 0 IN IP4 192.168.1.1
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<< s=No Title
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<< m=audio 0 RTP/AVP 14
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<< a=control:streamid=0
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- Parse the SDP message, for each stream (m=) we create an GstRTPStream. We need
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to allocate two local UDP ports for receiving the RTP and RTCP data because we
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need to send the port numbers to the server in the next request.
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In RTSPSrc we create two elements that can handle the udp://0.0.0.0:0 uri. This
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will create an udp source element. We get the port number by getting the "port"
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property of the element after setting the element to PAUSED.
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+-----------------+
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| +------------+ |
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| | udpsrc0 | |
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| | port=5000 | |
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| +------------+ |
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| +------------+ |
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| | udpsrc1 | |
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| | port=5001 | |
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| +------------+ |
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+-----------------+
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- Send a SETUP message to the server with the RTP ports. We get the setup URI from
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the a= attribute in the SDP message. This can be an absolute URL or a relative
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url.
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ex:
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>> SETUP rtsp://thread:5454/south-rtsp.mp3/streamid=0 RTSP/1.0
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>> CSeq: 1
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>> Transport: RTP/AVP/UDP;unicast;client_port=5000-5001,RTP/AVP/UDP;multicast,RTP/AVP/TCP
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>>
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<< RTSP/1.0 200 OK
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<< Transport: RTP/AVP/UDP;unicast;client_port=5000-5001;server_port=6000-6001
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<< CSeq: 1
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<< Date: Wed May 11 13:21:43 2005 GMT
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<< Session: 5d5cb94413288ccd
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<<
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The client needs to send the local ports to the server along with the supported
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transport types. The server selects the final transport which it returns in the
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Transport header field. The server also includes its ports where RTP and RTCP
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messages can be sent to.
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In the above example UDP was choosen as a transport. At this point the RTSPSrc element
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will furter configure its elements to process this stream.
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The RTSPSrc will create and connect an RTP session manager element and will
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connect it to the src pads of the udp element. The data pad from the RTP session
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manager is ghostpadded to RTPSrc.
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The RTCP pad of the rtpdec is routed to a new udpsink that sends data to the RTCP
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port of the server as returned in the Transport: header field.
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+---------------------------------------------+
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| +------------+ |
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| | udpsrc0 | +--------+ |
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| | port=5000 ----- rtpdec --------------------
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| +------------+ | | |
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| +------------+ | | +------------+ |
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| | udpsrc1 ----- RTCP ---- udpsink | |
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| | port=5001 | +--------+ | port=6001 | |
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| +------------+ +------------+ |
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+---------------------------------------------+
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The output type of rtpdec is configured as the media type specified in the SDP
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message.
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- All the elements are set to PAUSED/PLAYING and the PLAY RTSP message is
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sent.
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>> PLAY rtsp://thread:5454/south-rtsp.mp3 RTSP/1.0
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>> CSeq: 2
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>>
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<< RTSP/1.0 200 OK
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<< CSeq: 2
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<< Date: Wed May 11 13:21:43 2005 GMT
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<< Session: 5d5cb94413288ccd
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<<
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- The udp source elements receive data from that point and the RTP/RTCP messages
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are processed by the elements.
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- In the case of interleaved mode, the SETUP method yields:
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>> SETUP rtsp://thread:5454/south-rtsp.mp3/streamid=0 RTSP/1.0
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>> CSeq: 1
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>> Transport: RTP/AVP/UDP;unicast;client_port=5000-5001,RTP/AVP/UDP;multicast,RTP/AVP/TCP
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>>
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<< RTSP/1.0 200 OK
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<< Transport: RTP/AVP/TCP;interleaved=0-1
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<< CSeq: 1
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<< Date: Wed May 11 13:21:43 2005 GMT
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<< Session: 5d5cb94413288ccd
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<<
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This means that RTP/RTCP messages will be send on channel 0/1 respectively and that
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the data will be received on the same connection as the RTSP connection.
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At this point, we remove the UDP source elements as we don't need them anymore. We
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set up the rtpsess session manager element though as follows:
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+---------------------------------------------+
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| +------------+ |
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| | _loop() | +--------+ |
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| | ----- rtpses --------------------
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| | | | | |
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| | | | | +------------+ |
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| | ----- RTCP ---- udpsink | |
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| | | +--------+ | port=6001 | |
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| +------------+ +------------+ |
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+---------------------------------------------+
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We start an interal task to start reading from the RTSP connection waiting
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for data. The received data is then pushed to the rtpdec element.
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When reading from the RTSP connection we receive data packets in the
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following layout (see also RFC2326)
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$<1 byte channel><2 bytes length, big endian><length bytes of data>
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