Introduce layering controller interface for av1 encoder

Add TODOs into AV1 encoder wrapper where it suppose to be used.

Bug: webrtc:11404
Change-Id: If049066b84be72829867d5084827a7d275648a7b
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/174806
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31278}

modules/video_coding/codecs/av1/scalable_video_controller.h

@@ -0,0 +1,71 @@
+/*
+ *  Copyright (c) 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.
+ */
+#ifndef MODULES_VIDEO_CODING_CODECS_AV1_SCALABLE_VIDEO_CONTROLLER_H_
+#define MODULES_VIDEO_CODING_CODECS_AV1_SCALABLE_VIDEO_CONTROLLER_H_
+
+#include <vector>
+
+#include "absl/container/inlined_vector.h"
+#include "absl/types/optional.h"
+#include "api/transport/rtp/dependency_descriptor.h"
+#include "common_video/generic_frame_descriptor/generic_frame_info.h"
+
+namespace webrtc {
+
+// Controls how video should be encoded to be scalable. Outputs results as
+// buffer usage configuration for encoder and enough details to communicate the
+// scalability structure via dependency descriptor rtp header extension.
+class ScalableVideoController {
+ public:
+  struct StreamLayersConfig {
+    int num_spatial_layers = 1;
+    int num_temporal_layers = 1;
+  };
+  struct LayerFrameConfig {
+    // Id to match configuration returned by NextFrameConfig with
+    // (possibly modified) configuration passed back via OnEncoderDone.
+    // The meaning of the id is an implementation detail of
+    // the ScalableVideoController.
+    int id = 0;
+
+    // Indication frame should be encoded as a key frame. In particular when
+    // `is_keyframe=true` property `CodecBufferUsage::referenced` should be
+    // ignored and treated as false.
+    bool is_keyframe = false;
+
+    int spatial_id = 0;
+    int temporal_id = 0;
+    // Describes how encoder which buffers encoder allowed to reference and
+    // which buffers encoder should update.
+    absl::InlinedVector<CodecBufferUsage, kMaxEncoderBuffers> buffers;
+  };
+
+  virtual ~ScalableVideoController() = default;
+
+  // Returns video structure description for encoder to configure itself.
+  virtual StreamLayersConfig StreamConfig() const = 0;
+
+  // Returns video structure description in format compatible with
+  // dependency descriptor rtp header extension.
+  virtual FrameDependencyStructure DependencyStructure() const = 0;
+
+  // When `restart` is true, first `LayerFrameConfig` should have `is_keyframe`
+  // set to true.
+  // Returned vector shouldn't be empty.
+  virtual std::vector<LayerFrameConfig> NextFrameConfig(bool restart) = 0;
+
+  // Returns configuration to pass to EncoderCallback.
+  virtual absl::optional<GenericFrameInfo> OnEncodeDone(
+      LayerFrameConfig config) = 0;
+};
+
+}  // namespace webrtc
+
+#endif  // MODULES_VIDEO_CODING_CODECS_AV1_SCALABLE_VIDEO_CONTROLLER_H_