rtpjitterbuffer

rtpjitterbuffer — A buffer that deals with network jitter and other transmission faults

Synopsis

struct              GstRtpJitterBuffer;

Object Hierarchy

  GObject
   +----GInitiallyUnowned
         +----GstObject
               +----GstElement
                     +----GstRtpJitterBuffer

Properties

  "do-lost"                  gboolean              : Read / Write
  "drop-on-latency"          gboolean              : Read / Write
  "latency"                  guint                 : Read / Write
  "ts-offset"                gint64                : Read / Write
  "mode"                     RTPJitterBufferMode   : Read / Write
  "percent"                  gint                  : Read
  "do-retransmission"        gboolean              : Read / Write
  "rtx-delay"                gint                  : Read / Write
  "rtx-delay-reorder"        gint                  : Read / Write
  "rtx-retry-period"         gint                  : Read / Write
  "rtx-retry-timeout"        gint                  : Read / Write

Signals

  "clear-pt-map"                                   : Action
  "handle-sync"                                    : Run Last
  "on-npt-stop"                                    : Run Last
  "request-pt-map"                                 : Run Last
  "set-active"                                     : Action

Description

This element reorders and removes duplicate RTP packets as they are received from a network source.

The element needs the clock-rate of the RTP payload in order to estimate the delay. This information is obtained either from the caps on the sink pad or, when no caps are present, from the "request-pt-map" signal. To clear the previous pt-map use the "clear-pt-map" signal.

The rtpjitterbuffer will wait for missing packets up to a configurable time limit using the "latency" property. Packets arriving too late are considered to be lost packets. If the "do-lost" property is set, lost packets will result in a custom serialized downstream event of name GstRTPPacketLost. The lost packet events are usually used by a depayloader or other element to create concealment data or some other logic to gracefully handle the missing packets.

The jitterbuffer will use the DTS (or PTS if no DTS is set) of the incomming buffer and the rtptime inside the RTP packet to create a PTS on the outgoing buffer.

The jitterbuffer can also be configured to send early retransmission events upstream by setting the "do-retransmission" property. In this mode, the jitterbuffer tries to estimate when a packet should arrive and sends a custom upstream event named GstRTPRetransmissionRequest when the packet is considered late. The initial expected packet arrival time is calculated as follows:

  • If seqnum N arrived at time T, seqnum N+1 is expected to arrive at T + packet-spacing + "rtx-delay". The packet spacing is calculated from the DTS (or PTS is no DTS) of two consecutive RTP packets with different rtptime.

  • If seqnum N0 arrived at time T0 and seqnum Nm arrived at time Tm, seqnum Ni is expected at time Ti = T0 + i*(Tm - T0)/(Nm - N0). Any previously scheduled timeout is overwritten.

  • If seqnum N arrived, all seqnum older than N - "rtx-delay-reorder" are considered late immediately. This is to request fast feedback for abonormally reorder packets before any of the previous timeouts is triggered.

A late packet triggers the GstRTPRetransmissionRequest custom upstream event. After the initial timeout expires and the retransmission event is sent, the timeout is scheduled for T + "rtx-retry-timeout". If the missing packet did not arrive after "rtx-retry-timeout", a new GstRTPRetransmissionRequest is sent upstream and the timeout is rescheduled again for T + "rtx-retry-timeout". This repeats until "rtx-retry-period" elapsed, at which point no further retransmission requests are sent and the regular logic is performed to schedule a lost packet as discussed above.

This element acts as a live element and so adds "latency" to the pipeline.

This element will automatically be used inside rtpbin.

Example pipelines

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