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+/*
+ *  Copyright 2018 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 PC_SIMULCAST_DESCRIPTION_H_
+#define PC_SIMULCAST_DESCRIPTION_H_
+
+#include <stddef.h>
+
+#include <string>
+#include <vector>
+
+#include "absl/strings/string_view.h"
+
+namespace cricket {
+
+// Describes a Simulcast Layer.
+// Each simulcast layer has a rid as the identifier and a paused flag.
+// See also: https://tools.ietf.org/html/draft-ietf-mmusic-rid-15 for
+// an explanation about rids.
+struct SimulcastLayer final {
+  SimulcastLayer(absl::string_view rid, bool is_paused);
+
+  SimulcastLayer(const SimulcastLayer& other) = default;
+  SimulcastLayer& operator=(const SimulcastLayer& other) = default;
+  bool operator==(const SimulcastLayer& other) const;
+
+  std::string rid;
+  bool is_paused;
+};
+
+// Describes a list of Simulcast layers.
+// Simulcast layers are specified in order of preference.
+// Each layer can have a list of alternatives (in order of preference).
+// https://tools.ietf.org/html/draft-ietf-mmusic-sdp-simulcast-13#section-5.1
+// Example Usage:
+//   To populate a list that specifies the following:
+//     1. Layer 1 or Layer 2
+//     2. Layer 3
+//     3. Layer 4 or Layer 5
+//   Use the following code:
+//     SimulcastLayerList list;
+//     list.AddLayerWithAlternatives(
+//            {SimulcastLayer("1", false), SimulcastLayer("2", false});
+//     list.AddLayer("3");
+//     list.AddLayerWithAlternatives(
+//            {SimulcastLayer("4", false), SimulcastLayer("5", false});
+class SimulcastLayerList final {
+ public:
+  // Type definitions required by a container.
+  typedef size_t size_type;
+  typedef std::vector<SimulcastLayer> value_type;
+  typedef std::vector<std::vector<SimulcastLayer>>::const_iterator
+      const_iterator;
+
+  // Use to add a layer when there will be no alternatives.
+  void AddLayer(const SimulcastLayer& layer);
+
+  // Use to add a list of alternatives.
+  // The alternatives should be specified in order of preference.
+  void AddLayerWithAlternatives(const std::vector<SimulcastLayer>& layers);
+
+  // Read-only access to the contents.
+  // Note: This object does not allow removal of layers.
+  const_iterator begin() const { return list_.begin(); }
+
+  const_iterator end() const { return list_.end(); }
+
+  const std::vector<SimulcastLayer>& operator[](size_t index) const;
+
+  size_t size() const { return list_.size(); }
+  bool empty() const { return list_.empty(); }
+
+  // Provides access to all the layers in the simulcast without their
+  // association into groups of alternatives.
+  std::vector<SimulcastLayer> GetAllLayers() const;
+
+ private:
+  // TODO(amithi, bugs.webrtc.org/10075):
+  // Validate that rids do not repeat in the list.
+  std::vector<std::vector<SimulcastLayer>> list_;
+};
+
+// Describes the simulcast options of a video media section.
+// This will list the send and receive layers (along with their alternatives).
+// Each simulcast layer has an identifier (rid) and can optionally be paused.
+// The order of the layers (as well as alternates) indicates user preference
+// from first to last (most preferred to least preferred).
+// https://tools.ietf.org/html/draft-ietf-mmusic-sdp-simulcast-13#section-5.1
+class SimulcastDescription final {
+ public:
+  const SimulcastLayerList& send_layers() const { return send_layers_; }
+  SimulcastLayerList& send_layers() { return send_layers_; }
+
+  const SimulcastLayerList& receive_layers() const { return receive_layers_; }
+  SimulcastLayerList& receive_layers() { return receive_layers_; }
+
+  bool empty() const;
+
+ private:
+  // TODO(amithi, bugs.webrtc.org/10075):
+  // Validate that rids do not repeat in send and receive layers.
+  SimulcastLayerList send_layers_;
+  SimulcastLayerList receive_layers_;
+};
+
+}  // namespace cricket
+
+#endif  // PC_SIMULCAST_DESCRIPTION_H_