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85 lines
4.1 KiB
Text
85 lines
4.1 KiB
Text
RTP auxiliary stream design
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auxiliary elements
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------------------
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There are two kind of auxiliary elements, sender and receiver.
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Let's call them rtpauxsend and rtpauxreceive.
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rtpauxsend has always one sink pad and can have unlimited requested src pads.
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If only src pad then it works in SSRC-multiplexed mode, if several src pads
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then it works in session multiplexed mode.
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rtpauxreceive has always one ssrc pad and can have unlimited requested sink pads.
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If only one sink pad then it works in SSRC-multiplexed mode, if several sink pads
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then it works in session multiplexed mode.
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rtpbin and auxiliary elements
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----------------------------
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-- basic mecanism
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rtpbin knows for which session ids the given auxiliary element belong to.
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It's done through "set-aux-send", for rtpauxsend kind, and through
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"set-aux-receive" for rtpauxreceive kind.
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You can call those signals as much as needed for each auxiliary element.
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So for aux elements that work in SSRC-multiplexed mode this signal action is
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called only one time.
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The user has to call those action signals before to request the differents
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rtpbin pads.
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rtpbin is in charge to link those auxiliary elements with the sessions,
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and on receiver side, rtpbin has also to handle the link with ssrcdemux.
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rtpbin never knows if the given rtpauxsend is actually a rtprtxsend element
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or another aux element.
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rtpbin never knows if the given rtpauxreceive is actually a rtprtxreceive
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element or another aux element.
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rtpbin has to be kept generic so that more aux elements can be added later
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without changing rtpbin.
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It's currently not possible to use rtpbin with auxiliary stream from gst-launch.
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We can discuss about having the ability for rtpbin to instanciate itself
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the special aux elements rtprtxsend and rtprtxreceive but they need to be
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configured ("payload-type" and "payload-types" properties) to make retransmission
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work. So having several rtprtxsend and rtprtxreceive in a rtpbin would require
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a lot of properties to manage them form rtpbin.
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And for each auxiliary elements.
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If you want to use rtprtxreceive and rtprtpsend from gst-launch you have to use
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rtpsession, ssrcdemux and rtpjitterbuffer elements yourself.
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See gtk-doc of rtprtxreceive for an example.
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-- requesting the rtpbin's pads on the pipeline receiver side
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If rtpauxreceive is set for session, i, j, k then it has to call
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rtpbin::"set-aux-receive" 3 times giving those ids and this aux element.
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It has to be done before requesting the recv_rtp_sink_i, recv_rtp_sink_j, recv_rtp_sink_k.
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For a concrete case rtprtxreceive, if the user wants it for session i, then it has
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to call rtpbin::"set-aux-receive" one time giving i and this aux element.
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Then the user can request recv_rtp_sink_i pad.
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Calling rtpbin::"set-aux-receive" does not create the session. It add the given
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session id and aux element to a hashtable(key:session id, value: aux element).
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Then when the user ask for rtpbin.recv_rtp_sink_i, rtpbin lookup if there is an
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aux element for this i session id. If yes it requests a sink pad to this aux
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element and links it with the recv_rtp_src pad of the new gstrtpsession.
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rtpbin also checks that this aux element is connected only one time to ssrcdemux.
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Because rtpauxreceive has only one source pad.
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Each call to request rtpbin.recv_rtp_sink_k will also creates rtpbin.recv_rtp_src_k_ssrc_pt
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as usual. So that the user have it when then it requests rtpbin. (from gst-launch) or
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using on_rtpbinreceive_pad_added callback from an application.
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-- requesting the rtpbin's pads on the pipeline sender side
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For the sender this is similar but a bit more complicated to implement.
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When the user asks for rtpbin.send_rtp_sink_i, rtpbin will lookup in its
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second map (key:session id, value: aux send element). If there is one aux
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element, then it will set the sink pad of this aux sender element to be the ghost
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pad rtpbin.send_rtp_sink_i that the user asked. rtpbin will also request a src
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pad of this aux element to connect it to gstrtpsession_i. It will automatically
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create rtpbin.send_rtp_src_i the usuall way. Then if the user asks
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rtpbin.send_rtp_src_k, then rtpbin will also lookup in that map and request
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another source pad of the aux element and connect it to the new gstrtpsession_k.
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