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diff --git a/third_party/libwebrtc/modules/video_coding/svc/scalability_structure_simulcast.h b/third_party/libwebrtc/modules/video_coding/svc/scalability_structure_simulcast.h
new file mode 100644
index 0000000000..99be9f0d58
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+/*
+ *  Copyright (c) 2021 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.
+ */
+#ifndef MODULES_VIDEO_CODING_SVC_SCALABILITY_STRUCTURE_SIMULCAST_H_
+#define MODULES_VIDEO_CODING_SVC_SCALABILITY_STRUCTURE_SIMULCAST_H_
+
+#include <vector>
+
+#include "api/transport/rtp/dependency_descriptor.h"
+#include "api/video/video_bitrate_allocation.h"
+#include "common_video/generic_frame_descriptor/generic_frame_info.h"
+#include "modules/video_coding/svc/scalable_video_controller.h"
+
+namespace webrtc {
+
+// Scalability structure with multiple independent spatial layers each with the
+// same temporal layering.
+class ScalabilityStructureSimulcast : public ScalableVideoController {
+ public:
+  struct ScalingFactor {
+    int num = 1;
+    int den = 2;
+  };
+  ScalabilityStructureSimulcast(int num_spatial_layers,
+                                int num_temporal_layers,
+                                ScalingFactor resolution_factor);
+  ~ScalabilityStructureSimulcast() override;
+
+  StreamLayersConfig StreamConfig() const override;
+  std::vector<LayerFrameConfig> NextFrameConfig(bool restart) override;
+  GenericFrameInfo OnEncodeDone(const LayerFrameConfig& config) override;
+  void OnRatesUpdated(const VideoBitrateAllocation& bitrates) override;
+
+ private:
+  enum FramePattern {
+    kNone,
+    kDeltaT2A,
+    kDeltaT1,
+    kDeltaT2B,
+    kDeltaT0,
+  };
+  static constexpr int kMaxNumSpatialLayers = 3;
+  static constexpr int kMaxNumTemporalLayers = 3;
+
+  // Index of the buffer to store last frame for layer (`sid`, `tid`)
+  int BufferIndex(int sid, int tid) const {
+    return tid * num_spatial_layers_ + sid;
+  }
+  bool DecodeTargetIsActive(int sid, int tid) const {
+    return active_decode_targets_[sid * num_temporal_layers_ + tid];
+  }
+  void SetDecodeTargetIsActive(int sid, int tid, bool value) {
+    active_decode_targets_.set(sid * num_temporal_layers_ + tid, value);
+  }
+  FramePattern NextPattern() const;
+  bool TemporalLayerIsActive(int tid) const;
+
+  const int num_spatial_layers_;
+  const int num_temporal_layers_;
+  const ScalingFactor resolution_factor_;
+
+  FramePattern last_pattern_ = kNone;
+  std::bitset<kMaxNumSpatialLayers> can_reference_t0_frame_for_spatial_id_ = 0;
+  std::bitset<kMaxNumSpatialLayers> can_reference_t1_frame_for_spatial_id_ = 0;
+  std::bitset<32> active_decode_targets_;
+};
+
+// S1  0--0--0-
+//             ...
+// S0  0--0--0-
+class ScalabilityStructureS2T1 : public ScalabilityStructureSimulcast {
+ public:
+  explicit ScalabilityStructureS2T1(ScalingFactor resolution_factor = {})
+      : ScalabilityStructureSimulcast(2, 1, resolution_factor) {}
+  ~ScalabilityStructureS2T1() override = default;
+
+  FrameDependencyStructure DependencyStructure() const override;
+};
+
+class ScalabilityStructureS2T2 : public ScalabilityStructureSimulcast {
+ public:
+  explicit ScalabilityStructureS2T2(ScalingFactor resolution_factor = {})
+      : ScalabilityStructureSimulcast(2, 2, resolution_factor) {}
+  ~ScalabilityStructureS2T2() override = default;
+
+  FrameDependencyStructure DependencyStructure() const override;
+};
+
+// S1T2       3   7
+//            |  /
+// S1T1       / 5
+//           |_/
+// S1T0     1-------9...
+//
+// S0T2       2   6
+//            |  /
+// S0T1       / 4
+//           |_/
+// S0T0     0-------8...
+// Time->   0 1 2 3 4
+class ScalabilityStructureS2T3 : public ScalabilityStructureSimulcast {
+ public:
+  explicit ScalabilityStructureS2T3(ScalingFactor resolution_factor = {})
+      : ScalabilityStructureSimulcast(2, 3, resolution_factor) {}
+  ~ScalabilityStructureS2T3() override = default;
+
+  FrameDependencyStructure DependencyStructure() const override;
+};
+
+class ScalabilityStructureS3T1 : public ScalabilityStructureSimulcast {
+ public:
+  explicit ScalabilityStructureS3T1(ScalingFactor resolution_factor = {})
+      : ScalabilityStructureSimulcast(3, 1, resolution_factor) {}
+  ~ScalabilityStructureS3T1() override = default;
+
+  FrameDependencyStructure DependencyStructure() const override;
+};
+
+class ScalabilityStructureS3T2 : public ScalabilityStructureSimulcast {
+ public:
+  explicit ScalabilityStructureS3T2(ScalingFactor resolution_factor = {})
+      : ScalabilityStructureSimulcast(3, 2, resolution_factor) {}
+  ~ScalabilityStructureS3T2() override = default;
+
+  FrameDependencyStructure DependencyStructure() const override;
+};
+
+class ScalabilityStructureS3T3 : public ScalabilityStructureSimulcast {
+ public:
+  explicit ScalabilityStructureS3T3(ScalingFactor resolution_factor = {})
+      : ScalabilityStructureSimulcast(3, 3, resolution_factor) {}
+  ~ScalabilityStructureS3T3() override = default;
+
+  FrameDependencyStructure DependencyStructure() const override;
+};
+
+}  // namespace webrtc
+
+#endif  // MODULES_VIDEO_CODING_SVC_SCALABILITY_STRUCTURE_SIMULCAST_H_