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* Copyright 2015 The WebRTC project authors. All Rights Reserved.
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
#include <stdint.h>
#include <map>
#include <string>
#include <vector>
#include "absl/container/inlined_vector.h"
#include "absl/strings/string_view.h"
#include "absl/types/optional.h"
#include "api/media_types.h"
#include "api/priority.h"
#include "api/rtp_transceiver_direction.h"
#include "api/video/resolution.h"
#include "api/video_codecs/scalability_mode.h"
#include "rtc_base/system/rtc_export.h"
namespace webrtc {
// These structures are intended to mirror those defined by:
// Contains everything specified as of 2017 Jan 24.
// They are used when retrieving or modifying the parameters of an
// RtpSender/RtpReceiver, or retrieving capabilities.
// Note on conventions: Where ORTC may use "octet", "short" and "unsigned"
// types, we typically use "int", in keeping with our style guidelines. The
// parameter's actual valid range will be enforced when the parameters are set,
// rather than when the parameters struct is built. An exception is made for
// SSRCs, since they use the full unsigned 32-bit range, and aren't expected to
// be used for any numeric comparisons/operations.
// Additionally, where ORTC uses strings, we may use enums for things that have
// a fixed number of supported values. However, for things that can be extended
// (such as codecs, by providing an external encoder factory), a string
// identifier is used.
enum class FecMechanism {
// Used in RtcpFeedback struct.
enum class RtcpFeedbackType {
LNTF, // "goog-lntf"
REMB, // "goog-remb"
// Used in RtcpFeedback struct when type is NACK or CCM.
enum class RtcpFeedbackMessageType {
// Equivalent to {type: "nack", parameter: undefined} in ORTC.
PLI, // Usable with NACK.
FIR, // Usable with CCM.
enum class DtxStatus {
// Based on the spec in
// These options are enforced on a best-effort basis. For instance, all of
// these options may suffer some frame drops in order to avoid queuing.
// TODO(sprang): Look into possibility of more strictly enforcing the
// maintain-framerate option.
// TODO(deadbeef): Default to "balanced", as the spec indicates?
enum class DegradationPreference {
// Don't take any actions based on over-utilization signals. Not part of the
// web API.
// On over-use, request lower resolution, possibly causing down-scaling.
// On over-use, request lower frame rate, possibly causing frame drops.
// Try to strike a "pleasing" balance between frame rate or resolution.
RTC_EXPORT const char* DegradationPreferenceToString(
DegradationPreference degradation_preference);
RTC_EXPORT extern const double kDefaultBitratePriority;
struct RTC_EXPORT RtcpFeedback {
RtcpFeedbackType type = RtcpFeedbackType::CCM;
// Equivalent to ORTC "parameter" field with slight differences:
// 1. It's an enum instead of a string.
// 2. Generic NACK feedback is represented by a GENERIC_NACK message type,
// rather than an unset "parameter" value.
absl::optional<RtcpFeedbackMessageType> message_type;
// Constructors for convenience.
explicit RtcpFeedback(RtcpFeedbackType type);
RtcpFeedback(RtcpFeedbackType type, RtcpFeedbackMessageType message_type);
RtcpFeedback(const RtcpFeedback&);
bool operator==(const RtcpFeedback& o) const {
return type == o.type && message_type == o.message_type;
bool operator!=(const RtcpFeedback& o) const { return !(*this == o); }
struct RTC_EXPORT RtpCodec {
RtpCodec(const RtpCodec&);
virtual ~RtpCodec();
// Build MIME "type/subtype" string from `name` and `kind`.
std::string mime_type() const { return MediaTypeToString(kind) + "/" + name; }
// Used to identify the codec. Equivalent to MIME subtype.
std::string name;
// The media type of this codec. Equivalent to MIME top-level type.
cricket::MediaType kind = cricket::MEDIA_TYPE_AUDIO;
// If unset, the implementation default is used.
absl::optional<int> clock_rate;
// The number of audio channels used. Unset for video codecs. If unset for
// audio, the implementation default is used.
// TODO(deadbeef): The "implementation default" part isn't fully implemented.
// Only defaults to 1, even though some codecs (such as opus) should really
// default to 2.
absl::optional<int> num_channels;
// Feedback mechanisms to be used for this codec.
// TODO(deadbeef): Not implemented with PeerConnection senders/receivers.
std::vector<RtcpFeedback> rtcp_feedback;
// Codec-specific parameters that must be signaled to the remote party.
// Corresponds to "a=fmtp" parameters in SDP.
// Contrary to ORTC, these parameters are named using all lowercase strings.
// This helps make the mapping to SDP simpler, if an application is using SDP.
// Boolean values are represented by the string "1".
std::map<std::string, std::string> parameters;
bool operator==(const RtpCodec& o) const {
return name == && kind == o.kind && clock_rate == o.clock_rate &&
num_channels == o.num_channels && rtcp_feedback == o.rtcp_feedback &&
parameters == o.parameters;
bool operator!=(const RtpCodec& o) const { return !(*this == o); }
// RtpCodecCapability is to RtpCodecParameters as RtpCapabilities is to
// RtpParameters. This represents the static capabilities of an endpoint's
// implementation of a codec.
struct RTC_EXPORT RtpCodecCapability : public RtpCodec {
virtual ~RtpCodecCapability();
// Default payload type for this codec. Mainly needed for codecs that have
// statically assigned payload types.
absl::optional<int> preferred_payload_type;
// List of scalability modes supported by the video codec.
absl::InlinedVector<ScalabilityMode, kScalabilityModeCount> scalability_modes;
bool operator==(const RtpCodecCapability& o) const {
return RtpCodec::operator==(o) &&
preferred_payload_type == o.preferred_payload_type &&
scalability_modes == o.scalability_modes;
bool operator!=(const RtpCodecCapability& o) const { return !(*this == o); }
// Used in RtpCapabilities and RtpTransceiverInterface's header extensions query
// and setup methods; represents the capabilities/preferences of an
// implementation for a header extension.
// Just called "RtpHeaderExtension" in ORTC, but the "Capability" suffix was
// added here for consistency and to avoid confusion with
// RtpHeaderExtensionParameters.
// Note that ORTC includes a "kind" field, but we omit this because it's
// redundant; if you call "RtpReceiver::GetCapabilities(MEDIA_TYPE_AUDIO)",
// you know you're getting audio capabilities.
struct RTC_EXPORT RtpHeaderExtensionCapability {
// URI of this extension, as defined in RFC8285.
std::string uri;
// Preferred value of ID that goes in the packet.
absl::optional<int> preferred_id;
// If true, it's preferred that the value in the header is encrypted.
// TODO(deadbeef): Not implemented.
bool preferred_encrypt = false;
// The direction of the extension. The kStopped value is only used with
// RtpTransceiverInterface::SetHeaderExtensionsToNegotiate() and
// SetHeaderExtensionsToNegotiate().
RtpTransceiverDirection direction = RtpTransceiverDirection::kSendRecv;
// Constructors for convenience.
explicit RtpHeaderExtensionCapability(absl::string_view uri);
RtpHeaderExtensionCapability(absl::string_view uri, int preferred_id);
RtpHeaderExtensionCapability(absl::string_view uri,
int preferred_id,
RtpTransceiverDirection direction);
bool operator==(const RtpHeaderExtensionCapability& o) const {
return uri == o.uri && preferred_id == o.preferred_id &&
preferred_encrypt == o.preferred_encrypt && direction == o.direction;
bool operator!=(const RtpHeaderExtensionCapability& o) const {
return !(*this == o);
// RTP header extension, see RFC8285.
struct RTC_EXPORT RtpExtension {
enum Filter {
// Encrypted extensions will be ignored and only non-encrypted extensions
// will be considered.
// Encrypted extensions will be preferred but will fall back to
// non-encrypted extensions if necessary.
// Encrypted extensions will be required, so any non-encrypted extensions
// will be discarded.
RtpExtension(absl::string_view uri, int id);
RtpExtension(absl::string_view uri, int id, bool encrypt);
std::string ToString() const;
bool operator==(const RtpExtension& rhs) const {
return uri == rhs.uri && id == && encrypt == rhs.encrypt;
static bool IsSupportedForAudio(absl::string_view uri);
static bool IsSupportedForVideo(absl::string_view uri);
// Return "true" if the given RTP header extension URI may be encrypted.
static bool IsEncryptionSupported(absl::string_view uri);
// Returns the header extension with the given URI or nullptr if not found.
static const RtpExtension* FindHeaderExtensionByUri(
const std::vector<RtpExtension>& extensions,
absl::string_view uri,
Filter filter);
// Returns the header extension with the given URI and encrypt parameter,
// if found, otherwise nullptr.
static const RtpExtension* FindHeaderExtensionByUriAndEncryption(
const std::vector<RtpExtension>& extensions,
absl::string_view uri,
bool encrypt);
// Returns a list of extensions where any extension URI is unique.
// The returned list will be sorted by uri first, then encrypt and id last.
// Having the list sorted allows the caller fo compare filtered lists for
// equality to detect when changes have been made.
static const std::vector<RtpExtension> DeduplicateHeaderExtensions(
const std::vector<RtpExtension>& extensions,
Filter filter);
// Encryption of Header Extensions, see RFC 6904 for details:
static constexpr char kEncryptHeaderExtensionsUri[] =
// Header extension for audio levels, as defined in:
static constexpr char kAudioLevelUri[] =
// Header extension for RTP timestamp offset, see RFC 5450 for details:
static constexpr char kTimestampOffsetUri[] =
// Header extension for absolute send time, see url for details:
static constexpr char kAbsSendTimeUri[] =
// Header extension for absolute capture time, see url for details:
static constexpr char kAbsoluteCaptureTimeUri[] =
// Header extension for coordination of video orientation, see url for
// details:
static constexpr char kVideoRotationUri[] = "urn:3gpp:video-orientation";
// Header extension for video content type. E.g. default or screenshare.
static constexpr char kVideoContentTypeUri[] =
// Header extension for video timing.
static constexpr char kVideoTimingUri[] =
// Experimental codec agnostic frame descriptor.
static constexpr char kGenericFrameDescriptorUri00[] =
static constexpr char kDependencyDescriptorUri[] =
// Experimental extension for signalling target bitrate per layer.
static constexpr char kVideoLayersAllocationUri[] =
// Header extension for transport sequence number, see url for details:
static constexpr char kTransportSequenceNumberUri[] =
static constexpr char kTransportSequenceNumberV2Uri[] =
// This extension allows applications to adaptively limit the playout delay
// on frames as per the current needs. For example, a gaming application
// has very different needs on end-to-end delay compared to a video-conference
// application.
static constexpr char kPlayoutDelayUri[] =
// Header extension for color space information.
static constexpr char kColorSpaceUri[] =
// Header extension for identifying media section within a transport.
static constexpr char kMidUri[] = "urn:ietf:params:rtp-hdrext:sdes:mid";
// Header extension for RIDs and Repaired RIDs
static constexpr char kRidUri[] =
static constexpr char kRepairedRidUri[] =
// Header extension to propagate webrtc::VideoFrame id field
static constexpr char kVideoFrameTrackingIdUri[] =
// Header extension for Mixer-to-Client audio levels per CSRC as defined in
static constexpr char kCsrcAudioLevelsUri[] =
// Inclusive min and max IDs for two-byte header extensions and one-byte
// header extensions, per RFC8285 Section 4.2-4.3.
static constexpr int kMinId = 1;
static constexpr int kMaxId = 255;
static constexpr int kMaxValueSize = 255;
static constexpr int kOneByteHeaderExtensionMaxId = 14;
static constexpr int kOneByteHeaderExtensionMaxValueSize = 16;
std::string uri;
int id = 0;
bool encrypt = false;
struct RTC_EXPORT RtpFecParameters {
// If unset, a value is chosen by the implementation.
// Works just like RtpEncodingParameters::ssrc.
absl::optional<uint32_t> ssrc;
FecMechanism mechanism = FecMechanism::RED;
// Constructors for convenience.
explicit RtpFecParameters(FecMechanism mechanism);
RtpFecParameters(FecMechanism mechanism, uint32_t ssrc);
RtpFecParameters(const RtpFecParameters&);
bool operator==(const RtpFecParameters& o) const {
return ssrc == o.ssrc && mechanism == o.mechanism;
bool operator!=(const RtpFecParameters& o) const { return !(*this == o); }
struct RTC_EXPORT RtpRtxParameters {
// If unset, a value is chosen by the implementation.
// Works just like RtpEncodingParameters::ssrc.
absl::optional<uint32_t> ssrc;
// Constructors for convenience.
explicit RtpRtxParameters(uint32_t ssrc);
RtpRtxParameters(const RtpRtxParameters&);
bool operator==(const RtpRtxParameters& o) const { return ssrc == o.ssrc; }
bool operator!=(const RtpRtxParameters& o) const { return !(*this == o); }
struct RTC_EXPORT RtpEncodingParameters {
RtpEncodingParameters(const RtpEncodingParameters&);
// If unset, a value is chosen by the implementation.
// Note that the chosen value is NOT returned by GetParameters, because it
// may change due to an SSRC conflict, in which case the conflict is handled
// internally without any event. Another way of looking at this is that an
// unset SSRC acts as a "wildcard" SSRC.
absl::optional<uint32_t> ssrc;
// The relative bitrate priority of this encoding. Currently this is
// implemented for the entire rtp sender by using the value of the first
// encoding parameter.
// See:
// "very-low" = 0.5
// "low" = 1.0
// "medium" = 2.0
// "high" = 4.0
// TODO( Implement this per encoding parameter.
// Currently there is logic for how bitrate is distributed per simulcast layer
// in the VideoBitrateAllocator. This must be updated to incorporate relative
// bitrate priority.
double bitrate_priority = kDefaultBitratePriority;
// The relative DiffServ Code Point priority for this encoding, allowing
// packets to be marked relatively higher or lower without affecting
// bandwidth allocations. See .
// TODO( Implement this per encoding parameter.
// TODO( TCP connections should use a single
// DSCP value even if shared by multiple senders; this is not implemented.
Priority network_priority = Priority::kLow;
// If set, this represents the Transport Independent Application Specific
// maximum bandwidth defined in RFC3890. If unset, there is no maximum
// bitrate. Currently this is implemented for the entire rtp sender by using
// the value of the first encoding parameter.
// Just called "maxBitrate" in ORTC spec.
// TODO(deadbeef): With ORTC RtpSenders, this currently sets the total
// bandwidth for the entire bandwidth estimator (audio and video). This is
// just always how "b=AS" was handled, but it's not correct and should be
// fixed.
absl::optional<int> max_bitrate_bps;
// Specifies the minimum bitrate in bps for video.
absl::optional<int> min_bitrate_bps;
// Specifies the maximum framerate in fps for video.
absl::optional<double> max_framerate;
// Specifies the number of temporal layers for video (if the feature is
// supported by the codec implementation).
// Screencast support is experimental.
absl::optional<int> num_temporal_layers;
// For video, scale the resolution down by this factor.
absl::optional<double> scale_resolution_down_by;
absl::optional<std::string> scalability_mode;
// Requested encode resolution.
// This field provides an alternative to `scale_resolution_down_by`
// that is not dependent on the video source.
// When setting requested_resolution it is not necessary to adapt the
// video source using OnOutputFormatRequest, since the VideoStreamEncoder
// will apply downscaling if necessary. requested_resolution will also be
// propagated to the video source, this allows downscaling earlier in the
// pipeline which can be beneficial if the source is consumed by multiple
// encoders, but is not strictly necessary.
// The `requested_resolution` is subject to resource adaptation.
// It is an error to set both `requested_resolution` and
// `scale_resolution_down_by`.
absl::optional<Resolution> requested_resolution;
// For an RtpSender, set to true to cause this encoding to be encoded and
// sent, and false for it not to be encoded and sent. This allows control
// across multiple encodings of a sender for turning simulcast layers on and
// off.
// TODO( Updating this parameter will trigger an encoder
// reset, but this isn't necessarily required.
bool active = true;
// Value to use for RID RTP header extension.
// Called "encodingId" in ORTC.
std::string rid;
// Allow dynamic frame length changes for audio:
bool adaptive_ptime = false;
bool operator==(const RtpEncodingParameters& o) const {
return ssrc == o.ssrc && bitrate_priority == o.bitrate_priority &&
network_priority == o.network_priority &&
max_bitrate_bps == o.max_bitrate_bps &&
min_bitrate_bps == o.min_bitrate_bps &&
max_framerate == o.max_framerate &&
num_temporal_layers == o.num_temporal_layers &&
scale_resolution_down_by == o.scale_resolution_down_by &&
active == && rid == o.rid &&
adaptive_ptime == o.adaptive_ptime &&
requested_resolution == o.requested_resolution;
bool operator!=(const RtpEncodingParameters& o) const {
return !(*this == o);
struct RTC_EXPORT RtpCodecParameters : public RtpCodec {
RtpCodecParameters(const RtpCodecParameters&);
virtual ~RtpCodecParameters();
// Payload type used to identify this codec in RTP packets.
// This must always be present, and must be unique across all codecs using
// the same transport.
int payload_type = 0;
bool operator==(const RtpCodecParameters& o) const {
return RtpCodec::operator==(o) && payload_type == o.payload_type;
bool operator!=(const RtpCodecParameters& o) const { return !(*this == o); }
// RtpCapabilities is used to represent the static capabilities of an endpoint.
// An application can use these capabilities to construct an RtpParameters.
struct RTC_EXPORT RtpCapabilities {
// Supported codecs.
std::vector<RtpCodecCapability> codecs;
// Supported RTP header extensions.
std::vector<RtpHeaderExtensionCapability> header_extensions;
// Supported Forward Error Correction (FEC) mechanisms. Note that the RED,
// ulpfec and flexfec codecs used by these mechanisms will still appear in
// `codecs`.
std::vector<FecMechanism> fec;
bool operator==(const RtpCapabilities& o) const {
return codecs == o.codecs && header_extensions == o.header_extensions &&
fec == o.fec;
bool operator!=(const RtpCapabilities& o) const { return !(*this == o); }
struct RtcpParameters final {
RtcpParameters(const RtcpParameters&);
// The SSRC to be used in the "SSRC of packet sender" field. If not set, one
// will be chosen by the implementation.
// TODO(deadbeef): Not implemented.
absl::optional<uint32_t> ssrc;
// The Canonical Name (CNAME) used by RTCP (e.g. in SDES messages).
// If empty in the construction of the RtpTransport, one will be generated by
// the implementation, and returned in GetRtcpParameters. Multiple
// RtpTransports created by the same OrtcFactory will use the same generated
// If empty when passed into SetParameters, the CNAME simply won't be
// modified.
std::string cname;
// Send reduced-size RTCP?
bool reduced_size = false;
// Send RTCP multiplexed on the RTP transport?
// Not used with PeerConnection senders/receivers
bool mux = true;
bool operator==(const RtcpParameters& o) const {
return ssrc == o.ssrc && cname == o.cname &&
reduced_size == o.reduced_size && mux == o.mux;
bool operator!=(const RtcpParameters& o) const { return !(*this == o); }
struct RTC_EXPORT RtpParameters {
RtpParameters(const RtpParameters&);
// Used when calling getParameters/setParameters with a PeerConnection
// RtpSender, to ensure that outdated parameters are not unintentionally
// applied successfully.
std::string transaction_id;
// Value to use for MID RTP header extension.
// Called "muxId" in ORTC.
// TODO(deadbeef): Not implemented.
std::string mid;
std::vector<RtpCodecParameters> codecs;
std::vector<RtpExtension> header_extensions;
std::vector<RtpEncodingParameters> encodings;
// Only available with a Peerconnection RtpSender.
// In ORTC, our API includes an additional "RtpTransport"
// abstraction on which RTCP parameters are set.
RtcpParameters rtcp;
// When bandwidth is constrained and the RtpSender needs to choose between
// degrading resolution or degrading framerate, degradationPreference
// indicates which is preferred. Only for video tracks.
absl::optional<DegradationPreference> degradation_preference;
bool operator==(const RtpParameters& o) const {
return mid == o.mid && codecs == o.codecs &&
header_extensions == o.header_extensions &&
encodings == o.encodings && rtcp == o.rtcp &&
degradation_preference == o.degradation_preference;
bool operator!=(const RtpParameters& o) const { return !(*this == o); }
} // namespace webrtc