Add experimental extension RtpVideoLayersAllocation

The extension is suggested to be used for signaling per target bitrate, resolution
and frame rate to a SFU to allow a SFU to know what video layers a client is currently targeting.
It is hoped to replace the current Target bitrate RTCP XR message currently used only for screen share.

Bug: webrtc:12000
Change-Id: Id7b55e7ddaf6304e31839fd0482b096e1dbe8925
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/185980
Reviewed-by: Henrik Lundin <henrik.lundin@webrtc.org>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Commit-Queue: Per Kjellander <perkj@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32313}

api/video/BUILD.gn

diff --git a/api/video/BUILD.gn b/api/video/BUILD.gn
index 4d1d3e3..fd8363a 100644
--- a/api/video/BUILD.gn
+++ b/api/video/BUILD.gn
@@ -21,6 +21,7 @@
     "hdr_metadata.h",
     "video_content_type.cc",
     "video_content_type.h",
+    "video_layers_allocation.h",
     "video_rotation.h",
     "video_timing.cc",
     "video_timing.h",
@@ -30,8 +31,12 @@
     "..:array_view",
     "../../rtc_base:rtc_base_approved",
     "../../rtc_base/system:rtc_export",
+    "../units:data_rate",
   ]
-  absl_deps = [ "//third_party/abseil-cpp/absl/types:optional" ]
+  absl_deps = [
+    "//third_party/abseil-cpp/absl/container:inlined_vector",
+    "//third_party/abseil-cpp/absl/types:optional",
+  ]
 }
 
 rtc_library("video_frame") {

api/video/video_layers_allocation.h

diff --git a/api/video/video_layers_allocation.h b/api/video/video_layers_allocation.h
new file mode 100644
index 0000000..3973415
--- /dev/null
+++ b/api/video/video_layers_allocation.h
@@ -0,0 +1,77 @@
+/*
+ *  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 API_VIDEO_VIDEO_LAYERS_ALLOCATION_H_
+#define API_VIDEO_VIDEO_LAYERS_ALLOCATION_H_
+
+#include <cstdint>
+
+#include "absl/container/inlined_vector.h"
+#include "api/units/data_rate.h"
+
+namespace webrtc {
+
+// This struct contains additional stream-level information needed by a
+// Selective Forwarding Middlebox to make relay decisions of RTP streams.
+struct VideoLayersAllocation {
+  static constexpr int kMaxSpatialIds = 4;
+  static constexpr int kMaxTemporalIds = 4;
+
+  friend bool operator==(const VideoLayersAllocation& lhs,
+                         const VideoLayersAllocation& rhs) {
+    return lhs.rtp_stream_index == rhs.rtp_stream_index &&
+           lhs.resolution_and_frame_rate_is_valid ==
+               rhs.resolution_and_frame_rate_is_valid &&
+           lhs.active_spatial_layers == rhs.active_spatial_layers;
+  }
+
+  friend bool operator!=(const VideoLayersAllocation& lhs,
+                         const VideoLayersAllocation& rhs) {
+    return !(lhs == rhs);
+  }
+
+  struct SpatialLayer {
+    friend bool operator==(const SpatialLayer& lhs, const SpatialLayer& rhs) {
+      return lhs.rtp_stream_index == rhs.rtp_stream_index &&
+             lhs.spatial_id == rhs.spatial_id &&
+             lhs.target_bitrate_per_temporal_layer ==
+                 rhs.target_bitrate_per_temporal_layer &&
+             lhs.width == rhs.width && lhs.height == rhs.height &&
+             lhs.frame_rate_fps == rhs.frame_rate_fps;
+    }
+
+    friend bool operator!=(const SpatialLayer& lhs, const SpatialLayer& rhs) {
+      return !(lhs == rhs);
+    }
+    int rtp_stream_index = 0;
+    // Index of the spatial layer per `rtp_stream_index`.
+    int spatial_id = 0;
+    // Target bitrate per decode target.
+    absl::InlinedVector<DataRate, kMaxTemporalIds>
+        target_bitrate_per_temporal_layer;
+
+    // These fields are only valid if `resolution_and_frame_rate_is_valid` is
+    // true
+    uint16_t width = 0;
+    uint16_t height = 0;
+    // Max frame rate used in any temporal layer of this spatial layer.
+    uint8_t frame_rate_fps = 0;
+  };
+
+  // Index of the rtp stream this allocation is sent on. Used for mapping
+  // a SpatialLayer to a rtp stream.
+  int rtp_stream_index = 0;
+  bool resolution_and_frame_rate_is_valid = false;
+  absl::InlinedVector<SpatialLayer, kMaxSpatialIds> active_spatial_layers;
+};
+
+}  // namespace webrtc
+
+#endif  // API_VIDEO_VIDEO_LAYERS_ALLOCATION_H_