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design: rtp: add missing markup

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Reynaldo H. Verdejo Pinochet 2016-12-28 23:10:14 -08:00
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markdown/design/rtp.md
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@ -56,38 +56,38 @@ gtk-doc of rtprtxreceive for an example.
If rtpauxreceive is set for session, i, j, k then it has to call
rtpbin::"set-aux-receive" 3 times giving those ids and this aux element.
It has to be done before requesting the recv\_rtp\_sink\_i,
recv\_rtp\_sink\_j, recv\_rtp\_sink\_k. For a concrete case
It has to be done before requesting the `recv_rtp_sink_i`,
`recv_rtp_sink_j`, `recv_rtp_sink_k`. For a concrete case
rtprtxreceive, if the user wants it for session i, then it has to call
rtpbin::"set-aux-receive" one time giving i and this aux element. Then
the user can request recv\_rtp\_sink\_i pad.
the user can request `recv_rtp_sink_i` pad.
Calling rtpbin::"set-aux-receive" does not create the session. It add
the given session id and aux element to a hashtable(key:session id,
value: aux element). Then when the user ask for
rtpbin.recv\_rtp\_sink\_i, rtpbin lookup if there is an aux element for
`rtpbin.recv_rtp_sink_i`, rtpbin lookup if there is an aux element for
this i session id. If yes it requests a sink pad to this aux element and
links it with the recv\_rtp\_src pad of the new gstrtpsession. rtpbin
links it with the `recv_rtp_src` pad of the new gstrtpsession. rtpbin
also checks that this aux element is connected only one time to
ssrcdemux. Because rtpauxreceive has only one source pad. Each call to
request rtpbin.recv\_rtp\_sink\_k will also creates
rtpbin.recv\_rtp\_src\_k\_ssrc\_pt as usual. So that the user have it
request `rtpbin.recv_rtp_sink_k` will also creates
`rtpbin.recv_rtp_src_k_ssrc_pt` as usual. So that the user have it
when then it requests rtpbin. (from gst-launch) or using
on\_rtpbinreceive\_pad\_added callback from an application.
`on_rtpbinreceive_pad_added` callback from an application.
### Requesting the rtpbin's pads on the pipeline sender side
For the sender this is similar but a bit more complicated to implement.
When the user asks for rtpbin.send\_rtp\_sink\_i, rtpbin will lookup in
When the user asks for `rtpbin.send_rtp_sink_i`, rtpbin will lookup in
its second map (key:session id, value: aux send element). If there is
one aux element, then it will set the sink pad of this aux sender
element to be the ghost pad rtpbin.send\_rtp\_sink\_i that the user
element to be the ghost pad `rtpbin.send_rtp_sink_i` that the user
asked. rtpbin will also request a src pad of this aux element to connect
it to gstrtpsession\_i. It will automatically create
rtpbin.send\_rtp\_src\_i the usuall way. Then if the user asks
rtpbin.send\_rtp\_src\_k, then rtpbin will also lookup in that map and
it to `gstrtpsession_i`. It will automatically create
`rtpbin.send_rtp_src_i` the usuall way. Then if the user asks
`rtpbin.send_rtp_src_k`, then rtpbin will also lookup in that map and
request another source pad of the aux element and connect it to the new
gstrtpsession\_k.
`gstrtpsession_k`.
# RTP collision design
@ -105,7 +105,7 @@ collided SSRC are placed upstream from the gstrtpsession.
## rtppayloader
When handling a GstRTPCollision event, the rtppayloader has to choose
When handling a `GstRTPCollision` event, the rtppayloader has to choose
another ssrc.
## BYE only the corresponding source, not the whole session.
@ -134,7 +134,7 @@ gstrtpsession element when it receives a NACK from the network.
### Basic mechanism
rtprtxsend keeps a history of rtp packets that it has already sent. When
it receives the event GstRTPRetransmissionRequest from the downstream
it receives the event `GstRTPRetransmissionRequest` from the downstream
gstrtpsession element, it loopkup the requested seqnum in its stored
packets. If the packet is present in its history, it will create a RTX
packet according to RFC 4588. Then this rtx packet is pushed to its src
@ -160,8 +160,8 @@ master stream.
### Retransmission ssrc and seqnum
To choose rtx\_ssrc it randomly selects a number between 0 and 2^32-1
until it is different than master\_ssrc. rtx\_seqnum is randomly
To choose `rtx_ssrc` it randomly selects a number between 0 and 2^32-1
until it is different than `master_ssrc`. `rtx_seqnum` is randomly
selected between 0 and 2^16-1
### Deeper in the stored buffer history
@ -181,17 +181,17 @@ buffer into a GQueue to its tail. Before to send the current master
stream packet, rtprtxsend sends all the buffers which are in this
GQueue. Taking care of converting them to rtx packets. This way, rtx
packets are sent in the same order they have been requested.
(g\_list\_foreach traverse the queue from head to tail) The GQueue is
cleared between sending 2 master stream packets. So for this GQueue to
(`g_list_foreach` traverse the queue from head to tail) The `GQueue` is
cleared between sending 2 master stream packets. So for this `GQueue` to
contain more than one element, it means that rtprtxsend receives more
than one rtx request between sending 2 master packets.
### Collision
When handling a GstRTPCollision event, if the ssrc is its rtx ssrc then
When handling a `GstRTPCollision` event, if the ssrc is its rtx ssrc then
rtprtxsend clear its history and its pending retransmission queue. Then
it chooses a rtx\_ssrc until it's different than master ssrc. If the
GstRTPCollision event does not contain its rtx ssrc, for example its
it chooses a `rtx_ssrc` until it's different than master ssrc. If the
`GstRTPCollision` event does not contain its rtx ssrc, for example its
master ssrc or other, then it just forwards the event to upstream. So
that it can be handled by the rtppayloader.
@ -212,7 +212,7 @@ a given time. If bad luck then the association is delayed to the next
rtx request.
The algorithm also needs to know if a given packet is a rtx packet or
not. To know this information there is the rtx-payload-types property.
not. To know this information there is the `rtx-payload-types` property.
For now the user as to configure it but later it will be automatically
retreive this information from SDP. It needs to know if the current
packet is rtx or not in order to know if it can extract the OSN from the
@ -232,7 +232,7 @@ and src pad.
### Deeper in the association algorithm
When it receives a GstRTPRetransmissionRequest event it will remember
When it receives a `GstRTPRetransmissionRequest` event it will remember
the ssrc and the seqnum from this request.
On incoming packets, if the packet has its ssrc already associated then