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* Copyright 2020 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 <memory>
#include <utility>
#include <vector>
#include "absl/types/optional.h"
#include "absl/types/variant.h"
#include "api/adaptation/resource.h"
#include "api/rtp_parameters.h"
#include "api/video/video_adaptation_counters.h"
#include "api/video/video_stream_encoder_observer.h"
#include "call/adaptation/adaptation_constraint.h"
#include "call/adaptation/degradation_preference_provider.h"
#include "call/adaptation/video_source_restrictions.h"
#include "call/adaptation/video_stream_input_state.h"
#include "call/adaptation/video_stream_input_state_provider.h"
#include "modules/video_coding/utility/quality_scaler.h"
#include "rtc_base/experiments/balanced_degradation_settings.h"
#include "rtc_base/thread_annotations.h"
namespace webrtc {
// The listener is responsible for carrying out the reconfiguration of the video
// source such that the VideoSourceRestrictions are fulfilled.
class VideoSourceRestrictionsListener {
virtual ~VideoSourceRestrictionsListener();
// The |restrictions| are filtered by degradation preference but not the
// |adaptation_counters|, which are currently only reported for legacy stats
// calculation purposes.
virtual void OnVideoSourceRestrictionsUpdated(
VideoSourceRestrictions restrictions,
const VideoAdaptationCounters& adaptation_counters,
rtc::scoped_refptr<Resource> reason,
const VideoSourceRestrictions& unfiltered_restrictions) = 0;
class VideoStreamAdapter;
extern const int kMinFrameRateFps;
VideoSourceRestrictions FilterRestrictionsByDegradationPreference(
VideoSourceRestrictions source_restrictions,
DegradationPreference degradation_preference);
int GetHigherResolutionThan(int pixel_count);
// Either represents the next VideoSourceRestrictions the VideoStreamAdapter
// will take, or provides a Status code indicating the reason for not adapting
// if the adaptation is not valid.
class Adaptation final {
enum class Status {
// Applying this adaptation will have an effect. All other Status codes
// indicate that adaptation is not possible and why.
// Cannot adapt. The minimum or maximum adaptation has already been reached.
// There are no more steps to take.
// Cannot adapt. The resolution or frame rate requested by a recent
// adaptation has not yet been reflected in the input resolution or frame
// rate; adaptation is refused to avoid "double-adapting".
// Not enough input.
// Adaptation disabled via degradation preference.
// Adaptation up was rejected by a VideoAdaptationConstraint.
static const char* StatusToString(Status status);
Status status() const;
const VideoStreamInputState& input_state() const;
const VideoSourceRestrictions& restrictions() const;
const VideoAdaptationCounters& counters() const;
friend class VideoStreamAdapter;
// Constructs with a valid adaptation. Status is kValid.
Adaptation(int validation_id,
VideoSourceRestrictions restrictions,
VideoAdaptationCounters counters,
VideoStreamInputState input_state);
// Constructor when adaptation is not valid. Status MUST NOT be kValid.
Adaptation(int validation_id, Status invalid_status);
// An Adaptation can become invalidated if the state of VideoStreamAdapter is
// modified before the Adaptation is applied. To guard against this, this ID
// has to match VideoStreamAdapter::adaptation_validation_id_ when applied.
// TODO( Remove the validation_id_.
const int validation_id_;
const Status status_;
// Input state when adaptation was made.
const VideoStreamInputState input_state_;
const VideoSourceRestrictions restrictions_;
const VideoAdaptationCounters counters_;
// Owns the VideoSourceRestriction for a single stream and is responsible for
// adapting it up or down when told to do so. This class serves the following
// purposes:
// 1. Keep track of a stream's restrictions.
// 2. Provide valid ways to adapt up or down the stream's restrictions.
// 3. Modify the stream's restrictions in one of the valid ways.
class VideoStreamAdapter {
VideoStreamAdapter(VideoStreamInputStateProvider* input_state_provider,
VideoStreamEncoderObserver* encoder_stats_observer);
VideoSourceRestrictions source_restrictions() const;
const VideoAdaptationCounters& adaptation_counters() const;
void ClearRestrictions();
void AddRestrictionsListener(
VideoSourceRestrictionsListener* restrictions_listener);
void RemoveRestrictionsListener(
VideoSourceRestrictionsListener* restrictions_listener);
void AddAdaptationConstraint(AdaptationConstraint* adaptation_constraint);
void RemoveAdaptationConstraint(AdaptationConstraint* adaptation_constraint);
// TODO(hbos): Setting the degradation preference should not clear
// restrictions! This is not defined in the spec and is unexpected, there is a
// tiny risk that people would discover and rely on this behavior.
void SetDegradationPreference(DegradationPreference degradation_preference);
// Returns an adaptation that we are guaranteed to be able to apply, or a
// status code indicating the reason why we cannot adapt.
Adaptation GetAdaptationUp();
Adaptation GetAdaptationDown();
Adaptation GetAdaptationTo(const VideoAdaptationCounters& counters,
const VideoSourceRestrictions& restrictions);
// Tries to adapt the resolution one step. This is used for initial frame
// dropping. Does nothing if the degradation preference is not BALANCED or
// MAINTAIN_FRAMERATE. In the case of BALANCED, it will try twice to reduce
// the resolution. If it fails twice it gives up.
Adaptation GetAdaptDownResolution();
// Updates source_restrictions() the Adaptation.
void ApplyAdaptation(const Adaptation& adaptation,
rtc::scoped_refptr<Resource> resource);
struct RestrictionsWithCounters {
VideoSourceRestrictions restrictions;
VideoAdaptationCounters counters;
void BroadcastVideoRestrictionsUpdate(
const VideoStreamInputState& input_state,
const rtc::scoped_refptr<Resource>& resource);
bool HasSufficientInputForAdaptation(const VideoStreamInputState& input_state)
const RTC_RUN_ON(&sequence_checker_);
using RestrictionsOrState =
absl::variant<RestrictionsWithCounters, Adaptation::Status>;
RestrictionsOrState GetAdaptationUpStep(
const VideoStreamInputState& input_state) const
RestrictionsOrState GetAdaptationDownStep(
const VideoStreamInputState& input_state,
const RestrictionsWithCounters& current_restrictions) const
RestrictionsOrState GetAdaptDownResolutionStepForBalanced(
const VideoStreamInputState& input_state) const
RestrictionsOrState AdaptIfFpsDiffInsufficient(
const VideoStreamInputState& input_state,
const RestrictionsWithCounters& restrictions) const
Adaptation GetAdaptationUp(const VideoStreamInputState& input_state) const
Adaptation GetAdaptationDown(const VideoStreamInputState& input_state) const
static RestrictionsOrState DecreaseResolution(
const VideoStreamInputState& input_state,
const RestrictionsWithCounters& current_restrictions);
static RestrictionsOrState IncreaseResolution(
const VideoStreamInputState& input_state,
const RestrictionsWithCounters& current_restrictions);
// Framerate methods are member functions because they need internal state
// if the degradation preference is BALANCED.
RestrictionsOrState DecreaseFramerate(
const VideoStreamInputState& input_state,
const RestrictionsWithCounters& current_restrictions) const
RestrictionsOrState IncreaseFramerate(
const VideoStreamInputState& input_state,
const RestrictionsWithCounters& current_restrictions) const
struct RestrictionsOrStateVisitor;
Adaptation RestrictionsOrStateToAdaptation(
RestrictionsOrState step_or_state,
const VideoStreamInputState& input_state) const
SequenceChecker sequence_checker_ RTC_GUARDED_BY(&sequence_checker_);
// Gets the input state which is the basis of all adaptations.
// Thread safe.
VideoStreamInputStateProvider* input_state_provider_;
// Used to signal when min pixel limit has been reached.
VideoStreamEncoderObserver* const encoder_stats_observer_;
// Decides the next adaptation target in DegradationPreference::BALANCED.
const BalancedDegradationSettings balanced_settings_;
// To guard against applying adaptations that have become invalidated, an
// Adaptation that is applied has to have a matching validation ID.
int adaptation_validation_id_ RTC_GUARDED_BY(&sequence_checker_);
// When deciding the next target up or down, different strategies are used
// depending on the DegradationPreference.
DegradationPreference degradation_preference_
// Used to avoid adapting twice. Stores the resolution at the time of the last
// adaptation.
// TODO(hbos): Can we implement a more general "cooldown" mechanism of
// resources intead? If we already have adapted it seems like we should wait
// a while before adapting again, so that we are not acting on usage
// measurements that are made obsolete/unreliable by an "ongoing" adaptation.
struct AwaitingFrameSizeChange {
AwaitingFrameSizeChange(bool pixels_increased, int frame_size);
const bool pixels_increased;
const int frame_size_pixels;
absl::optional<AwaitingFrameSizeChange> awaiting_frame_size_change_
// The previous restrictions value. Starts as unrestricted.
VideoSourceRestrictions last_video_source_restrictions_
VideoSourceRestrictions last_filtered_restrictions_
std::vector<VideoSourceRestrictionsListener*> restrictions_listeners_
std::vector<AdaptationConstraint*> adaptation_constraints_
RestrictionsWithCounters current_restrictions_
} // namespace webrtc