rtpjitterbuffer

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

Properties

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

Signals

void clear-pt-map Action
void handle-sync Run Last
void on-npt-stop Run Last
GstCaps* request-pt-map Run Last
guint64 set-active Action

Types and Values

Object Hierarchy

    GObject
    ╰── GInitiallyUnowned
        ╰── GstObject
            ╰── GstElement
                ╰── GstRtpJitterBuffer

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

1
gst-launch-1.0 rtspsrc location=rtsp://192.168.1.133:8554/mpeg1or2AudioVideoTest ! rtpjitterbuffer ! rtpmpvdepay ! mpeg2dec ! xvimagesink
Connect to a streaming server and decode the MPEG video. The jitterbuffer is inserted into the pipeline to smooth out network jitter and to reorder the out-of-order RTP packets.

Synopsis

Element Information

plugin

rtpmanager

author

Philippe Kalaf <philippe.kalaf@collabora.co.uk>, Wim Taymans <wim.taymans@gmail.com>

class

Filter/Network/RTP

Element Pads

name

sink

direction

sink

presence

always

details

application/x-rtp, clock-rate=(int)[ 1, 2147483647 ]

name

sink_rtcp

direction

sink

presence

request

details

application/x-rtcp

name

src

direction

source

presence

always

details

application/x-rtp

Functions

Types and Values

struct GstRtpJitterBuffer

struct GstRtpJitterBuffer;

Opaque jitterbuffer structure.

Property Details

The “do-lost” property

  “do-lost”                  gboolean

Send out a GstRTPPacketLost event downstream when a packet is considered lost.

Flags: Read / Write

Default value: FALSE


The “drop-on-latency” property

  “drop-on-latency”          gboolean

Drop oldest buffers when the queue is completely filled.

Flags: Read / Write

Default value: FALSE


The “latency” property

  “latency”                  guint

The maximum latency of the jitterbuffer. Packets will be kept in the buffer for at most this time.

Flags: Read / Write

Default value: 200


The “ts-offset” property

  “ts-offset”                gint64

Adjust GStreamer output buffer timestamps in the jitterbuffer with offset. This is mainly used to ensure interstream synchronisation.

Flags: Read / Write

Default value: 0


The “mode” property

  “mode”                     RTPJitterBufferMode

Control the buffering and timestamping mode used by the jitterbuffer.

Flags: Read / Write

Default value: Slave receiver to sender clock


The “percent” property

  “percent”                  gint

The percent of the jitterbuffer that is filled.

Flags: Read

Allowed values: [0,100]

Default value: 0


The “do-retransmission” property

  “do-retransmission”        gboolean

Send out a GstRTPRetransmission event upstream when a packet is considered late and should be retransmitted.

Flags: Read / Write

Default value: FALSE

Since 1.2


The “rtx-delay” property

  “rtx-delay”                gint

When a packet did not arrive at the expected time, wait this extra amount of time before sending a retransmission event.

When -1 is used, the max jitter will be used as extra delay.

Flags: Read / Write

Allowed values: >= G_MAXULONG

Default value: -1

Since 1.2


The “rtx-delay-reorder” property

  “rtx-delay-reorder”        gint

Assume that a retransmission event should be sent when we see this much packet reordering.

When -1 is used, the value will be estimated based on observed packet reordering.

Flags: Read / Write

Allowed values: >= G_MAXULONG

Default value: 3

Since 1.2


The “rtx-retry-period” property

  “rtx-retry-period”         gint

The amount of time to try to get a retransmission.

When -1 is used, the value will be estimated based on the jitterbuffer latency and the observed round trip time.

Flags: Read / Write

Allowed values: >= G_MAXULONG

Default value: -1

Since 1.2


The “rtx-retry-timeout” property

  “rtx-retry-timeout”        gint

Retry sending a transmission event after this timeout in ms (-1 automatic).

Flags: Read / Write

Allowed values: >= G_MAXULONG

Default value: -1


The “stats” property

  “stats”                    GstStructure *

Various jitterbuffer statistics. This property returns a GstStructure with name application/x-rtp-jitterbuffer-stats with the following fields:

"rtx-count" G_TYPE_UINT64 The number of retransmissions requested "rtx-success-count" G_TYPE_UINT64 The number of successful retransmissions "rtx-per-packet" G_TYPE_DOUBLE Average number of RTX per packet "rtx-rtt" G_TYPE_UINT64 Average round trip time per RTX

Flags: Read

Since 1.4

Signal Details

The “clear-pt-map” signal

void
user_function (GstRtpJitterBuffer *buffer,
               gpointer            user_data)

Invalidate the clock-rate as obtained with the “request-pt-map” signal.

Parameters

buffer

the object which received the signal

 

user_data

user data set when the signal handler was connected.

 

Flags: Action


The “handle-sync” signal

void
user_function (GstRtpJitterBuffer *buffer,
               GstStructure       *struct,
               gpointer            user_data)

Be notified of new sync values.

Parameters

buffer

the object which received the signal

 

struct

a GstStructure containing sync values.

 

user_data

user data set when the signal handler was connected.

 

Flags: Run Last


The “on-npt-stop” signal

void
user_function (GstRtpJitterBuffer *buffer,
               gpointer            user_data)

Signal that the jitterbufer has pushed the RTP packet that corresponds to the npt-stop position.

Parameters

buffer

the object which received the signal

 

user_data

user data set when the signal handler was connected.

 

Flags: Run Last


The “request-pt-map” signal

GstCaps*
user_function (GstRtpJitterBuffer *buffer,
               guint               pt,
               gpointer            user_data)

Request the payload type as GstCaps for pt .

Parameters

buffer

the object which received the signal

 

pt

the pt

 

user_data

user data set when the signal handler was connected.

 

Flags: Run Last


The “set-active” signal

guint64
user_function (GstRtpJitterBuffer *buffer,
               gboolean            Returns,
               guint64             arg2,
               gpointer            user_data)

Start pushing out packets with the given base time. This signal is only useful in buffering mode.

Parameters

buffer

the object which received the signal

 

user_data

user data set when the signal handler was connected.

 

Returns

the time of the last pushed packet.

Flags: Action