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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<link href="webrtc-stats.css" rel="stylesheet" type="text/css">
<title>
Identifiers for WebRTC's Statistics API
</title>
<script class="remove" src="https://www.w3.org/Tools/respec/respec-w3c">
</script>
<script class="remove" src="webrtc-stats.js">
</script>
<!-- TODO Redundant since webidl2.js is already loaded in ReSpec, but not sure how to access it -->
<script class="remove" src="webidl2.js"></script>
</head>
<body>
<section id="abstract">
<p>
This document defines a set of WebIDL objects that allow access to the statistical
information about a {{RTCPeerConnection}}.
</p>
<p>
These objects are returned from the getStats API that is specified in [[WEBRTC]].
</p>
</section>
<section id="sotd">
<!-- Status of the draft -->
<p>Since the previous publication as a Candidate Recommendation, the stats objects were significantly reorganized to better match the underlying data sources. In addition, the <code>networkType</code> property was deprecated for preserving privacy, and the <code>statsended</code> event was removed as no longer needed.</p>
</section><!-- NB: [[!..]] normative refs, [[..]] informative refs-->
<!-- based on the wiki page https://www.w3.org/2011/04/webrtc/wiki/Stats -->
<section class="informative">
<h2>
Introduction
</h2>
<p>
Audio, video, or data packets transmitted over a peer-connection can be lost, and
experience varying amounts of network delay. A web application implementing WebRTC expects
to monitor the performance of the underlying network and media pipeline.
</p>
<p>
This document defines the statistic identifiers used by the web application to extract
metrics from the user agent.
</p>
</section>
<section id="conformance">
<p>
This specification defines the conformance criteria that applies to a single product: the
<em>user agent</em>.
</p>
<p>
Implementations that use ECMAScript to implement the objects defined in this specification
MUST implement them in a manner consistent with the
ECMAScript Bindings defined in the Web IDL specification [[WEBIDL]], as this document uses
that specification and terminology.
</p>
<p>
This specification does not define what objects a conforming implementation should
generate. Specifications that refer to this specification have the need to specify
conformance. They should put in their document text like this (EXAMPLE ONLY):
</p>
<ul>
<li>An implementation MUST support generating statistics for the type
{{RTCInboundRtpStreamStats}}, with members {{RTCReceivedRtpStreamStats/packetsReceived}}, {{RTCInboundRtpStreamStats/bytesReceived}}, {{RTCReceivedRtpStreamStats/packetsLost}}, and
{{RTCReceivedRtpStreamStats/jitter}}.
</li>
<li>It MUST support generating statistics for the type {{RTCOutboundRtpStreamStats}}, with
members {{RTCSentRtpStreamStats/packetsSent}}, {{RTCSentRtpStreamStats/bytesSent}}.
</li>
<li>For all subclasses of {{RTCRtpStreamStats}}, it MUST include {{RTCRtpStreamStats/ssrc}} and {{RTCRtpStreamStats/kind}}. When stats
exist for both sides of a connection, in the form of an {{RTCStatsType/"inbound-rtp"}} / {{RTCStatsType/"remote-outbound-rtp"}}
pair or an {{RTCStatsType/"outbound-rtp"}} / {{RTCStatsType/"remote-inbound-rtp"}} pair, the members {{RTCOutboundRtpStreamStats/remoteId}} and {{RTCRemoteOutboundRtpStreamStats/localId}} MUST
also be present.
</li>
<li>It MAY support generating other stats.
</li>
</ul>
</section>
<section>
<h2>
Terminology
</h2>
<p>
The terms {{RTCPeerConnection}}, {{RTCDataChannel}},
{{RTCDtlsTransport}}, {{RTCDtlsTransportState}}, {{RTCIceTransport}},
{{RTCIceRole}}, {{RTCIceTransportState}}, {{RTCDataChannelState}},
{{RTCIceCandidateType}}, {{RTCStats}}, {{RTCCertificate}} are defined in [[!WEBRTC]].
</p>
<p><dfn class=fixme data-idl>RTCPriorityType</dfn> is defined in [[WEBRTC-PRIORITY]].</p>
<p>
The term <dfn><a href="https://datatracker.ietf.org/doc/html/rfc7656#section-2.1.10">RTP stream</a></dfn> is defined in [[RFC7656]].
</p>
<p>
The terms <dfn data-lt="SSRC"><a href="https://datatracker.ietf.org/doc/html/rfc3550#section-3">Synchronization Source</a></dfn> (SSRC),
<dfn data-lt="Sender Report|SR|RTCP SR"><a href="https://datatracker.ietf.org/doc/html/rfc3550#section-6.4.1">RTCP Sender Report</a></dfn> (SR),
<dfn data-lt="Receiver Report|RR|RTCP RR"><a href="https://datatracker.ietf.org/doc/html/rfc3550#section-6.4.2">RTCP Receiver Report</a></dfn> (RR) are defined in [[RFC3550]].
</p>
<p>The term <dfn data-lt="Extended Report|XR"><a href="https://datatracker.ietf.org/doc/html/rfc3611">RTCP Extended Report</a></dfn> (XR) is defined in [[RFC3611]].</p>
<p>An <dfn>audio sample</dfn> refers to having a sample in any channel of an audio track - if multiple audio channels are used, metrics based on samples do not increment at a higher rate, simultaneously having samples in multiple channels counts as a single sample.</p>
</section>
<section>
<h2>
Basic concepts
</h2>
<p>
The basic object of the stats model is the [= stats object =]. The following terms are
defined to describe it:
</p>
<dl>
<dt>
<dfn data-export>Monitored object</dfn>
</dt>
<dd>
<p>
An internal object that keeps a set of data values. Most monitored objects are object
defined in the WebRTC API; they may be thought of as being internal properties of those
objects.
</p>
</dd>
<dt>
<dfn data-export>Stats object</dfn>
</dt>
<dd>
This is a set of values, copied out from a monitored object at a specific moment in time.
It is returned as a WebIDL dictionary through the getStats API call.
</dd>
<dt>
<dfn data-export>Stats object reference</dfn>
</dt>
<dd>
<p>
A monitored object has a stable identifier <var>id</var>, which is reflected in all stats
objects produced from the monitored object. Stats objects may contain references to
other stats objects using this <var>id</var> value. In a [= stats object =], these references
are represented by a {{DOMString}} containing <var>id</var> value of the referenced stats object.
</p>
<p>
All stats object references have type {{DOMString}} and member names ending in <code>Id</code>, or
they have type <code>sequence<{{DOMString}}></code> and member names ending in <code>Ids</code>.
</p>
</dd>
<dt>
<dfn data-export>Stats value</dfn>
</dt>
<dd>
Refers to a single value within a stats object.
</dd>
</dl>
<p>
A monitored object changes the values it contains continuously over its lifetime, but is
never visible through the getStats API call. A stats object, once returned, never changes.
</p>
<p>
The stats API is defined in [[!WEBRTC]]. It is defined to return a collection of [= stats object =]s, each of which is a dictionary inheriting directly or indirectly from the
<dfn class="informative" data-noexport>RTCStats</dfn> dictionary.
This API is normatively defined in [[!WEBRTC]], but is
reproduced here for ease of reference.
</p>
<pre class="idl informative">
dictionary RTCStats {
required DOMHighResTimeStamp timestamp;
required RTCStatsType type;
required DOMString id;
};
</pre>
<p>
Timestamps are expressed with {{DOMHighResTimeStamp}} [[HIGHRES-TIME]], and are defined as
{{Performance.timeOrigin}} +
{{Performance.now()}} at the time the information is
collected.
</p>
<section>
<h3>
Guidelines for design of stats objects
</h3>
<p>
When introducing a new stats object, the following principles should be followed:
</p>
<ul>
<li>An {{RTCStats}} object should correspond to an object defined in the specification it
supports.
</li>
<li>The object MUST define a new value in the {{RTCStatsType}} enum, and MUST define the
syntax of the [= stats object =] it returns either by reference to an existing
sub-dictionary of {{RTCStats}} or by defining a new sub-dictionary of {{RTCStats}}.
</li>
<li>All members of the new object need to have definitions that make them consistently
implementable. References to other specifications are a good way of doing this.
</li>
<li>All members need to have defined behavior for what happens before the thing it counts
happens, or when the information it's supposed to show is not available. Usually, this
will be "start at zero" or "do not populate the value".
</li>
</ul>
<p>
The new members of the stats dictionary need to be named according to standard practice
(camelCase), as per [[API-DESIGN-PRINCIPLES]].
</p>
<p>
Names ending in <code>Id</code> (such as {{RTCRtpStreamStats/transportId}}) are always a [= stats object reference =];
names ending in <code>Ids</code> are always of type sequence<{{DOMString}}>, where
each {{DOMString}} is a [= stats object reference =].
</p>
<p>
If the natural name for a stats value would end in <code>id</code> (such as when the stats value is
an in-protocol identifier for the monitored object), the recommended practice is to let
the name end in <code>identifier</code>, such as {{RTCDataChannelStats/dataChannelIdentifier}}.
</p>
<p>
Stats are sampled by Javascript. In general, an application will not have overall control
over how often stats are sampled, and the implementation cannot know what the intended
use of the stats is. There is, by design, no control surface for the application to
influence how stats are generated.
</p>
<p>
Therefore, letting the implementation compute "average" rates is not a good idea, since
that implies some averaging time interval that can't be set beforehand. Instead, the
recommended approach is to count the number of measurements of a value and sum the
measurements given even if the sum is meaningless in itself; the JS application can then
compute averages over any desired time interval by calling getStats() twice, taking the
difference of the two sums and dividing by the difference of the two counts.
</p>
<p>
For stats that are measured against time, such as byte counts, no separate counter is
needed; one can instead divide by the difference in the timestamps.
</p>
</section>
<section>
<h3>
Guidelines for implementing stats objects
</h3>
<p>
When implementing stats objects, the following guidelines should be adhered to:
</p>
<ul>
<li>When a feature is not implemented on the platform, omit the dictionary member that is
tracking usage of the feature.
</li>
<li>When a feature is not applicable to an instance of an object (for example {{RTCInboundRtpStreamStats/audioLevel}}
on a video stream), it shall not [= map/exist =]. Do NOT report a count of zero, -1 or "empty string".
</li>
<li>When a feature is an instantaneous measure and it has not yet been
sampled, it shall not [= map/exist =].</li>
<li>When a feature is a cumulative measure and it has not been sampled yet,
but is likely to increment in the future, report a
count of zero. This allows subtraction of such features without additional checks for existence.
</li>
</ul>
</section>
<section>
<h3>
Lifetime considerations for monitored objects
</h3>
<p>
The object descriptions will say what the lifetime of a [= monitored object =] from the
perspective of stats is. When a monitored object is <dfn>deleted</dfn>, it no longer appears in
stats; until this happens, it will appear. This may or may not correspond to the actual
lifetime of an object in an implementation; what matters for this specification is what
appears in stats.
</p>
<p>
If a monitored object can only exist in a few instances over the lifetime of a
{{RTCPeerConnection}}, it may be simplest to consider it "eternal" and never delete it from
the set of objects reported on in stats. This type of object will remain visible until
the {{RTCPeerConnection}} is no longer available; it is also visible in {{RTCPeerConnection/getStats()}} after
pc.close(). This is the default when no lifetime is mentioned in its specification.
</p>
<p>
Objects that might exist in many instances over time should have a defined time at which
they are [= deleted =], at which time they stop appearing in subsequent calls to {{RTCPeerConnection/getStats()}}.
When an object is [= deleted =], we can guarantee that no subsequent {{RTCPeerConnection/getStats()}} call will
contain a [= stats object reference =] that references the deleted object. We also
guarantee that the stats id of the deleted object will never be reused for another
object. This ensures that an application that collects [= stats object =]s for deleted
[= monitored object =]s will always be able to uniquely identify the object pointed to
in the result of any {{RTCPeerConnection/getStats()}} call.
</p>
</section>
<section>
<h3>
Guidelines for {{RTCPeerConnection/getStats()}} results caching/throttling
</h3>
<p>
A call to {{RTCPeerConnection/getStats()}} touches many components of WebRTC and may take significant time to
execute. The implementation may or may not utilize caching or throttling of {{RTCPeerConnection/getStats()}}
calls for performance benefits, however any implementation must adhere to the following:
</p>
<p>
When the state of the {{RTCPeerConnection}} visibly changes as a result of an API call, a
promise resolving or an event firing, subsequent new {{RTCPeerConnection/getStats()}} calls must return
up-to-date dictionaries for the affected objects.
</p>
<p>
When a stats object is [= deleted =], subsequent {{RTCPeerConnection/getStats()}} calls MUST NOT return stats
for that [= monitored object =].
</p>
</section>
</section><!-- VS: getStats() remains in base spec! -->
<section>
<h2>
Maintenance procedures for stats object types
</h2>
<section>
<h3>
Adding new stats objects
</h3>
<p class="status-ED">
This document, in its editors' draft form, serves as the repository for the currently
defined set of stats object types including proposals for new standard types.
</p>
<p class="status-not-ED">
This document specifies the interoperable stats object types. Proposals for new object
types may be made in <a href="https://w3c.github.io/webrtc-stats/">the editors draft
maintained on GitHub</a>. New standard types may appear in future revisions of the W3C
Recommendation.
</p>
<p>
If a need for a new stats object type or stats value within a stats object is found, an
issue should be <a href="https://github.com/w3c/webrtc-stats/issues">raised on
Github</a>, and a review process will decide on whether the stat should be added to the
editors draft or not.
</p>
<p>
A pull request for a change to the editors draft may serve as guidance for the
discussion, but the eventual merge is dependent on the review process.
</p>
<p>
While the WebRTC WG exists, it will serve as the review body; once it has disbanded, the
W3C will have to establish appropriate review.
</p>
<p>
The level of review sought is that of the IETF process' "expert review", as defined in
[[RFC5226]] section 4.1. The documentation needed includes the names of the new stats,
their data types, and the definitions they are based on, specified to a level that allows
interoperable implementation. The specification may consist of references to other
documents.
</p>
<p>
Another specification that wishes to refer to a specific version (for instance for
conformance) should refer to a dated version; these will be produced regularly when
updates happen.
</p>
</section>
</section>
<section>
<h2>
Procedures for mitigating privacy concerns
</h2>
<p class="fingerprint">
The WebRTC's Statistics API exposes information about the system,
including hardware capabilities and network characteristics. To limit
the finger printing surface imposed by this API, some metrics are only
exposed if allowed by the algorithms in this section.
</p>
<section>
<h3>
Limiting exposure of hardware capabilities
</h3>
<p>
To avoid passive fingerprinting, hardware capabilities should only be
exposed in capturing contexts. This is tested using the algorithm
below.
</p>
<p>
To <dfn data-lt="exposing hardware is allowed">check if hardware
exposure is allowed</dfn>, run the following steps:
<ol>
<li>
<p>
If the <a href="https://w3c.github.io/mediacapture-main/#context-capturing-state">
context capturing state</a> is true, return true.
</p>
</li>
<li>
<p>
Otherwise return false.
</p>
</li>
</ol>
</p>
</section>
</section>
<section id="rtctatstype-*">
<h2>
{{RTCStatsType}}
</h2>
<p>
The {{RTCStats/type}} member, of type {{RTCStatsType}}, indicates the type of the
object that the {{RTCStats}} object represents. An object with a given {{RTCStats/type}} can
have only one IDL dictionary type, but multiple {{RTCStats/type}} values may indicate the same IDL
dictionary type; for example, {{RTCStatsType/"local-candidate"}} and {{RTCStatsType/"remote-candidate"}} both use the IDL
dictionary type {{RTCIceCandidateStats}}.
</p>
<p>
This specification is normative for the allowed values of {{RTCStatsType}}.
</p>
<section id="rtcstatstype-str*">
<h3>
<dfn>RTCStatsType</dfn> enum
</h3>
<pre class="idl">
enum RTCStatsType {
"codec",
"inbound-rtp",
"outbound-rtp",
"remote-inbound-rtp",
"remote-outbound-rtp",
"media-source",
"media-playout",
"peer-connection",
"data-channel",
"transport",
"candidate-pair",
"local-candidate",
"remote-candidate",
"certificate"
};
</pre>
<p>
The following strings are valid values for {{RTCStatsType}}:
</p>
<dl data-link-for="RTCStatsType" data-dfn-for="RTCStatsType">
<dt>
<dfn>codec</dfn>
</dt>
<dd>
<p>
Statistics for a codec that is currently being used by <a>RTP stream</a>s being sent or
received by this {{RTCPeerConnection}} object. It is accessed by the
{{RTCCodecStats}}.
</p>
</dd>
<dt>
<dfn>inbound-rtp</dfn>
</dt>
<dd>
<p>
Statistics for an inbound <a>RTP stream</a> that is currently received with this
{{RTCPeerConnection}} object. It is accessed by the
{{RTCInboundRtpStreamStats}}.
</p>
<p>
RTX streams do not show up as separate
{{RTCInboundRtpStreamStats}} objects but affect the {{RTCReceivedRtpStreamStats/packetsReceived}},
{{RTCInboundRtpStreamStats/bytesReceived}}, {{RTCInboundRtpStreamStats/retransmittedPacketsReceived}}
and {{RTCInboundRtpStreamStats/retransmittedBytesReceived}} counters of the relevant
{{RTCInboundRtpStreamStats}} objects.
</p>
<p>
FEC streams do not show up as separate
{{RTCInboundRtpStreamStats}} objects but affect the {{RTCReceivedRtpStreamStats/packetsReceived}},
{{RTCInboundRtpStreamStats/bytesReceived}}, {{RTCInboundRtpStreamStats/fecPacketsReceived}}
and {{RTCInboundRtpStreamStats/fecBytesReceived}} counters of the relevant
{{RTCInboundRtpStreamStats}} objects.
</p>
</dd>
<dt>
<dfn>outbound-rtp</dfn>
</dt>
<dd>
<p>
Statistics for an outbound <a>RTP stream</a> that is currently sent with this
{{RTCPeerConnection}} object. It is accessed by the
{{RTCOutboundRtpStreamStats}}.
</p>
<p>
When there are multiple <a>RTP stream</a>s connected to the same sender due to using
simulcast, there will be one {{RTCOutboundRtpStreamStats}} per <a>RTP stream</a>,
with distinct values of the {{RTCRtpStreamStats/ssrc}} member. RTX streams do not show up as separate
{{RTCOutboundRtpStreamStats}} objects but affect the {{RTCSentRtpStreamStats/packetsSent}},
{{RTCSentRtpStreamStats/bytesSent}}, {{RTCOutboundRtpStreamStats/retransmittedPacketsSent}}
and {{RTCOutboundRtpStreamStats/retransmittedBytesSent}} counters of the relevant
{{RTCOutboundRtpStreamStats}} objects.
</p>
</dd>
<dt>
<dfn>remote-inbound-rtp</dfn>
</dt>
<dd>
<p>
Statistics for the remote endpoint's inbound <a>RTP stream</a> corresponding to an outbound
stream that is currently sent with this {{RTCPeerConnection}} object. It is
measured at the remote endpoint and reported in an <a>RTCP Receiver Report</a> (RR) or <a>RTCP
Extended Report</a> (XR). It is accessed by the
{{RTCRemoteInboundRtpStreamStats}}.
</p>
</dd>
<dt>
<dfn>remote-outbound-rtp</dfn>
</dt>
<dd>
<p>
Statistics for the remote endpoint's outbound <a>RTP stream</a> corresponding to an inbound
stream that is currently received with this {{RTCPeerConnection}} object. It
is measured at the remote endpoint and reported in an <a>RTCP Sender Report</a> (SR). It is
accessed by the {{RTCRemoteOutboundRtpStreamStats}}.
</p>
</dd>
<dt>
<dfn>media-source</dfn>
</dt>
<dd>
<p>
Statistics for the media produced by a {{MediaStreamTrack}} that is
currently attached to an {{RTCRtpSender}}. This reflects the media that is
fed to the encoder; after <code class=gum>getUserMedia()</code> constraints have been applied
(i.e. not the raw media produced by the camera). It is either an
{{RTCAudioSourceStats}} or {{RTCVideoSourceStats}}
depending on its <code class=gum>kind</code>.
</p>
</dd>
<dt>
<dfn>media-playout</dfn>
</dt>
<dd>
<p>
Statistics related to audio playout. It is accessed by the
{{RTCAudioPlayoutStats}}.
</p>
</dd>
<dt>
<dfn>peer-connection</dfn>
</dt>
<dd>
<p>
Statistics related to the {{RTCPeerConnection}} object. It is accessed by
the {{RTCPeerConnectionStats}}.
</p>
</dd>
<dt>
<dfn>data-channel</dfn>
</dt>
<dd>
<p>
Statistics related to each {{RTCDataChannel}} id. It is accessed by the
{{RTCDataChannelStats}}.
</p>
</dd>
<dt>
<dfn>transport</dfn>
</dt>
<dd>
<p>
Transport statistics related to the {{RTCPeerConnection}} object. It is
accessed by the {{RTCTransportStats}}.
</p>
</dd>
<dt>
<dfn>candidate-pair</dfn>
</dt>
<dd>
<p>
ICE candidate pair statistics related to the {{RTCIceTransport}} objects. It
is accessed by the {{RTCIceCandidatePairStats}}.
</p>
<p>
A candidate pair that is not the current pair for a transport is [= deleted =] when the
{{RTCIceTransport}} does an ICE restart, at the time the state changes to {{RTCIceTransportState/"new"}}. The
candidate pair that is the current pair for a transport is [= deleted =] after an ICE
restart when the {{RTCIceTransport}} switches to using a candidate pair generated from
the new candidates; this time doesn't correspond to any other externally observable
event.
</p>
</dd>
<dt>
<dfn>local-candidate</dfn>
</dt>
<dd>
<p>
ICE local candidate statistics related to the {{RTCIceTransport}} objects.
It is accessed by the {{RTCIceCandidateStats}} for the local
candidate.
</p>
<p>
A local candidate is [= deleted =] when the {{RTCIceTransport}} does an ICE restart, and the
candidate is no longer a member of any non-deleted candidate pair.
</p>
</dd>
<dt>
<dfn>remote-candidate</dfn>
</dt>
<dd>
<p>
ICE remote candidate statistics related to the {{RTCIceTransport}} objects.
It is accessed by the {{RTCIceCandidateStats}} for the remote
candidate.
</p>
<p>
A remote candidate is [= deleted =] when the {{RTCIceTransport}} does an ICE restart, and the
candidate is no longer a member of any non-deleted candidate pair.
</p>
</dd>
<dt>
<dfn>certificate</dfn>
</dt>
<dd>
<p>
Information about a certificate used by an {{RTCIceTransport}}. It is accessed by the
{{RTCCertificateStats}}.
</p>
</dd>
</dl>
</section>
</section>
<section>
<h2>
Stats dictionaries
</h2>
<section>
<h3>
The RTP statistics hierarchy
</h3>
<p>
The dictionaries for RTP statistics are structured as a hierarchy, so that those stats
that make sense in many different contexts are represented just once in IDL.
</p>
<p>
The metrics exposed here correspond to local measurements and those reported by RTCP packets.
Compound RTCP packets contain multiple RTCP report blocks, such as <a>Sender Report</a> (SR) and
<a>Receiver Report</a> (RR) whereas a non-compound RTCP packets may contain just a single
RTCP SR or RR block.
</p>
<p>
The lifetime of all RTP [= monitored object =]s are tied to <a>SSRC</a>s.
The {{RTCOutboundRtpStreamStats}} is created when the RTP sender is configured by
setting a local or remote SDP answer (via <code>setLocalDescription()</code>
or <code>setRemoteDescription()</code> and the signaling state returning to
<code>"stable"</code>). The {{RTCInboundRtpStreamStats}} is created when
the first RTP packet for this SSRC is received and the remote RTP stream stats
objects ({{RTCRemoteInboundRtpStreamStats}} and {{RTCRemoteOutboundRtpStreamStats}})
are created when the corresponding RTCP packet is first received.
</p>
<p>
RTP monitored objects are deleted when the corresponding RTP sender or
RTP receiver is reconfigured to remove the corresponding RTP stream.
This happens for the old SSRC when the {{RTCRtpStreamStats/ssrc}}
changes, a simulcast layer is dropped or the {{RTCRtpTransceiver}}'s
{{RTCRtpTransceiver/currentDirection}} becomes <code>"stopped"</code>.
The monitored object is <i>not</i> deleted if the transceiver is made
<code>"inactive"</code> or if the encoding's
{{RTCRtpEncodingParameters/active}} parameter is set to
<code>false</code>. If an SSRC is recycled after a deletion event has
happened, this is considered a new RTP monitored object and the new
RTP stream stats will have reset counters and a new ID.
</p>
<p>
For a given RTP stats object, its total counters must always increase,
but due to changes in SSRC, simulcast layers dropping or transceivers
stopping, an RTP stats object can be deleted and/or replaced by a new
RTP stats object. The caller will need to be aware of this when aggregating
packet counters accross multiple RTP stats objects (the aggregates may
decrease due to deletions).
</p>
<pre class="example highlight">
An RTCRtpSender is sending two layers of simulcast (on SSRC=111 and
SSRC=222). Two "outbound-rtp" stats objects are observed, one with
SSRC=111, and the other with SSRC=222. Both objects' packet counters are
increasing.
One layer is inactivated using RTCRtpSender.setParameters(). While
this pauses one of the layers (its packet counter freezes), the RTP
monitored objects are not deleted. The RTCRtpTransceiver is negotiated
as "inactive" and the RTP monitored objects are still not deleted.
When the RTCRtpTransceiver becomes "sendonly" again, the same
"outbound-rtp" objects continue to be used.
Later, RTCRtpTransceiver.stop() is called. The "outbound-rtp" objects
still exist but their packet counters have frozen. Renegotiation
happens and the transceiver.currentDirection becomes "stopped", now
both "outbound-rtp" objects have been deleted.
</pre>
<p>
The hierarchy is as follows:
</p>
<p>
{{RTCRtpStreamStats}}: Stats that apply to any end of any <a>RTP stream</a>
</p>
<ul>
<li>
<p>
{{RTCReceivedRtpStreamStats}}: Stats measured at the receiving end of an RTP
stream, known either because they're measured locally or transmitted via an RTCP
<a>Receiver Report</a> (RR) or <a>Extended Report</a> (XR) block.
</p>
<ul>
<li>
<p>
{{RTCInboundRtpStreamStats}}: Stats that can only be measured at the local
receiving end of an <a>RTP stream</a>.
</p>
</li>
<li>
<p>
{{RTCRemoteInboundRtpStreamStats}}: Stats relevant to the remote receiving end
of an <a>RTP stream</a> - usually computed by combining local data with data received
via an RTCP <a>RR</a> or <a>XR</a> block.
</p>
</li>
</ul>
</li>
<li>
<p>
{{RTCSentRtpStreamStats}}: Stats measured at the sending end of an <a>RTP stream</a>,
known either because they're measured locally or because they're received via RTCP,
usually in an <a>RTCP Sender Report</a> (SR).
</p>
<ul>
<li>
{{RTCOutboundRtpStreamStats}}: Stats measured locally.
</li>
<li>
<p>
{{RTCRemoteOutboundRtpStreamStats}}: Stats relevant to the remote sending end
of an <a>RTP stream</a>, usually computed based on an <a>RTCP SR</a>.
</p>
</li>
</ul>
</li>
</ul>
</section>
<section id="streamstats-dict*">
<h3>
<dfn>RTCRtpStreamStats</dfn> dictionary
</h3>
<div>
<pre class="idl">dictionary RTCRtpStreamStats : RTCStats {
required unsigned long ssrc;
required DOMString kind;
DOMString transportId;
DOMString codecId;
};</pre>
<section>
<h2>
Dictionary {{RTCRtpStreamStats}} Members
</h2>
<dl data-link-for="RTCRtpStreamStats" data-dfn-for="RTCRtpStreamStats" class=
"dictionary-members">
<dt>
<dfn>ssrc</dfn> of type <span class="idlMemberType">unsigned
long</span>
</dt>
<dd>
<p>
The synchronization source (SSRC) identifier is an unsigned integer value per [[RFC3550]]
used to identify the stream of RTP packets that this stats object is describing.
</p>
<p>
For outbound and inbound local, SSRC describes the stats for the RTP stream that were
sent and received, respectively by those endpoints.
For the remote inbound and remote outbound, SSRC describes the stats for the RTP stream
that were received by and sent to the remote endpoint.
</p>
</dd>
<dt>
<dfn>kind</dfn> of type <span class="idlMemberType">DOMString</span>
</dt>
<dd>
<p>
Either "<code class=gum>audio</code>" or "<code class=gum>video</code>". This
MUST match the <code class=gum>kind</code> attribute of the related {{MediaStreamTrack}}.
</p>
</dd>
<dt>
<dfn>transportId</dfn> of type <span class=
"idlMemberType">DOMString</span>
</dt>
<dd>
<p>
It is a unique identifier that is associated to the object that was inspected to
produce the {{RTCTransportStats}} associated with this <a>RTP stream</a>.
</p>
</dd>
<dt>
<dfn>codecId</dfn> of type <span class=
"idlMemberType">DOMString</span>
</dt>
<dd>
<p>
It is a unique identifier that is associated to the object that was inspected to
produce the {{RTCCodecStats}} associated with this <a>RTP stream</a>.
</p>
</dd>
</dl>
</section>
</div>
</section>
<section id="codec-dict*">
<h3>
<dfn>RTCCodecStats</dfn> dictionary
</h3>
<p>
Codecs are created when registered for an RTP transport,
but only the subset of codecs that are in use (referenced by an RTP
stream) are exposed in <code>getStats()</code>.
</p>
<p>
The {{RTCCodecStats}} object is created when one or more
{{RTCRtpStreamStats/codecId}} references the codec. When there no
longer exists any reference to the {{RTCCodecStats}}, the stats object
is deleted. If the same codec is used again in the future, the
{{RTCCodecStats}} object is revived with the same {{RTCStats/id}} as
before.
</p>
<p>
Codec objects may be referenced by multiple RTP streams in
media sections using the same transport, but similar codecs in
different transports have different {{RTCCodecStats}} objects.
</p>
<p class="note">
User agents are expected to coalesce information into a single
<code>"codec"</code> entry per payload type per transport, unless
{{RTCCodecStats/sdpFmtpLine}} differs per direction, in which case two
entries (one for encode and one for decode) are needed.
</p>
<div>
<pre class="idl">dictionary RTCCodecStats : RTCStats {
required unsigned long payloadType;
required DOMString transportId;
required DOMString mimeType;
unsigned long clockRate;
unsigned long channels;
DOMString sdpFmtpLine;
};</pre>
<section>
<h2>
Dictionary {{RTCCodecStats}} Members
</h2>
<dl data-link-for="RTCCodecStats" data-dfn-for="RTCCodecStats" class=
"dictionary-members">
<dt>
<dfn>payloadType</dfn> of type <span class="idlMemberType">unsigned
long</span>
</dt>
<dd>
<p>
Payload type as used in RTP encoding or decoding.
</p>
</dd>
<dt>
<dfn>transportId</dfn> of type <span class=
"idlMemberType">DOMString</span>
</dt>
<dd>
<p>
The unique identifier of the transport on which this codec is being used, which
can be used to look up the corresponding {{RTCTransportStats}}
object.
</p>
</dd>
<dt>
<dfn>mimeType</dfn> of type <span class=
"idlMemberType">DOMString</span>
</dt>
<dd>
<p>
The codec MIME media type/subtype defined in the IANA media types registry
[[!IANA-MEDIA-TYPES]], e.g. video/VP8.
</p>
</dd>
<dt>
<dfn>clockRate</dfn> of type <span class="idlMemberType">unsigned
long</span>
</dt>
<dd>
<p>
Represents the media sampling rate.
</p>
</dd>
<dt>
<dfn>channels</dfn> of type <span class="idlMemberType">unsigned
long</span>
</dt>
<dd>
<p>
When present, indicates the number of channels (mono=1, stereo=2).
</p>
</dd>
<dt>
<dfn>sdpFmtpLine</dfn> of type <span class=
"idlMemberType">DOMString</span>
</dt>
<dd>
<p>
The "format specific parameters" field from the
<code class="sdp">a=fmtp</code> line in the SDP
corresponding to the codec, if one [= map/exist =]s,
as defined by
[[!RFC8829]] (<a href="https://www.rfc-editor.org/rfc/rfc8829#section-5.8">section 5.8</a>).
</p>
</dd>
</dl>
</section>
</div>
</section>
<section id="receivedrtpstats-dict*">
<h3>
<dfn>RTCReceivedRtpStreamStats</dfn> dictionary
</h3>
<div>
<pre class="idl">dictionary RTCReceivedRtpStreamStats : RTCRtpStreamStats {
unsigned long long packetsReceived;
unsigned long long packetsReceivedWithEct1;
unsigned long long packetsReceivedWithCe;
unsigned long long packetsReportedAsLost;
unsigned long long packetsReportedAsLostButRecovered;
long long packetsLost;
double jitter;
};</pre>
<section>
<h2>
Dictionary {{RTCReceivedRtpStreamStats}} Members
</h2>
<dl data-link-for="RTCReceivedRtpStreamStats" data-dfn-for="RTCReceivedRtpStreamStats"
class="dictionary-members">
<dt>
<dfn>packetsReceived</dfn> of type <span class=
"idlMemberType">unsigned long long</span>
</dt>
<dd>
<p>
Total number of RTP packets received for this <a>SSRC</a>. This includes retransmissions.
At the receiving endpoint, this is calculated as defined in [[!RFC3550]] section 6.4.1. At the sending
endpoint the {{packetsReceived}} is estimated by subtracting the Cumulative Number of Packets Lost
from the Extended Highest Sequence Number Received, both reported in the <a>RTCP Receiver
Report</a>, and then subtracting the initial Extended Sequence Number that was sent to this SSRC in a
<a>RTCP Sender Report</a> and then adding one, to mirror what is discussed in Appendix A.3 in [[!RFC3550]], but for the
sender side. If no <a>RTCP Receiver Report</a> has been received yet, then return 0.
</p>
</dd>
<dt>
<dfn>packetsReceivedWithEct1</dfn> of type <span class="idlMemberType">unsigned long long</span>
</dt>
<dd>
<p>
Total number of RTP packets received for this <a>SSRC</a> marked with the "ECT(1)" marking.
</p>
</dd>
<dt>
<dfn>packetsReceivedWithCe</dfn> of type <span class="idlMemberType">unsigned long long</span>
</dt>
<dd>
<p>
Total number of RTP packets received for this <a>SSRC</a> marked with the "CE" marking.
</p>
</dd>
<dt>
<dt>
<dfn>packetsReportedAsLost</dfn> of type <span class="idlMemberType">unsigned long long</span>
</dt>
<dd>
<p>
Total number of RTP packets for which an [[RFC8888]] section 3.1 report has been sent with a zero R bit.
Only reported if support for the "ccfb" feedback mechanism has been negotiated.
</p>
</dd>
<dt><dfn>packetsReportedAsLostButRecovered</dfn> of type <span class="idlMemberType">unsigned long long</span></dt>
</dt>
<dd>
<p>
Total number of RTP packets for which an [[RFC8888]] section 3.1 report has been sent with a zero R bit,
but a later report for the same packet has the R bit set to 1.
Only reported if support for the "ccfb" feedback mechanism has been negotiated.
</p>
</dd>
<dt>
<dfn>packetsLost</dfn> of type <span class="idlMemberType">long long</span>
</dt>
<dd>
<p>
Total number of RTP packets lost for this <a>SSRC</a>. Calculated as defined in
[[!RFC3550]] section 6.4.1. Note that because of how this is estimated, it can be
negative if more packets are received than sent.
</p>
</dd>
<dt>
<dfn>jitter</dfn> of type <span class="idlMemberType">double</span>
</dt>
<dd>
<p>
Packet Jitter measured in seconds for this <a>SSRC</a>. Calculated as defined in section
6.4.1. of [[!RFC3550]].
</p>
</dd>
</dl>
</section>
</div>
</section>
<section id="inboundrtpstats-dict*">
<h3>
{{RTCInboundRtpStreamStats}} dictionary
</h3>
<p>
The <dfn>RTCInboundRtpStreamStats</dfn> dictionary represents the measurement metrics for
the incoming RTP media stream. The timestamp reported in the statistics object is the
time at which the data was sampled.
</p>
<div>
<pre class="idl">dictionary RTCInboundRtpStreamStats : RTCReceivedRtpStreamStats {
required DOMString trackIdentifier;
DOMString mid;
DOMString remoteId;