Add RTCP packet class for signaling encoder target bitrate.

webrtc/modules/rtp_rtcp/source/rtcp_packet/target_bitrate.cc

Index: webrtc/modules/rtp_rtcp/source/rtcp_packet/target_bitrate.cc
diff --git a/webrtc/modules/rtp_rtcp/source/rtcp_packet/target_bitrate.cc b/webrtc/modules/rtp_rtcp/source/rtcp_packet/target_bitrate.cc
new file mode 100644
index 0000000000000000000000000000000000000000..e3a813a85430ecf0841051e1f13287ae85afe28c
--- /dev/null
+++ b/webrtc/modules/rtp_rtcp/source/rtcp_packet/target_bitrate.cc
@@ -0,0 +1,134 @@
+/*
+ *  Copyright (c) 2016 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 "webrtc/modules/rtp_rtcp/source/rtcp_packet/target_bitrate.h"
+
+#include "webrtc/base/checks.h"
+#include "webrtc/base/logging.h"
+#include "webrtc/modules/rtp_rtcp/source/byte_io.h"
+
+namespace webrtc {
+namespace rtcp {
+constexpr size_t kTargetBitrateHeaderSizeBytes = 4;
+constexpr uint8_t TargetBitrate::kBlockType;
+const size_t TargetBitrate::kBitrateItemSizeBytes = 4;
+
+TargetBitrate::BitrateItem::BitrateItem()
+    : spatial_layer(0), temporal_layer(0), target_bitrate_kbps(0) {}
+
+TargetBitrate::BitrateItem::BitrateItem(uint8_t spatial_layer,
+                                        uint8_t temporal_layer,
+                                        uint32_t target_bitrate_kbps)
+    : spatial_layer(spatial_layer),
+      temporal_layer(temporal_layer),
+      target_bitrate_kbps(target_bitrate_kbps) {}
+
+//  RFC 4585: Feedback format.
+//
+//  Common packet format:
+//
+//   0                   1                   2                   3
+//   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+//  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+//  |     BT=42     |   reserved    |         block length          |
+//  +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
+//
+//  Target bitrate item (repeat as many times as necessary).
+//
+//  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+//  |   S   |   T   |                Target Bitrate                 |
+//  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+//  :  ...                                                          :
+//
+//  Spatial Layer (S): 4 bits
+//    Indicates which temporal layer this bitrate concerns.
+//
+//  Temporal Layer (T): 4 bits
+//    Indicates which temporal layer this bitrate concerns.
+//
+//  Target Bitrate: 24 bits
+//    The encoder target bitrate for this layer, in kbps.
+//
+//  As an example of how S and T are intended to be used, VP8 simulcast will
+//  use a separate TargetBitrate message per stream, since they are transmitted
+//  on separate SSRCs, with temporal layers grouped by stream.
+//  If VP9 SVC is used, there will be only one SSRC, so each spatial and
+//  temporal layer combo used shall be specified in the TargetBitrate packet.
+
+TargetBitrate::TargetBitrate() {}
+TargetBitrate::~TargetBitrate() {}
+
+void TargetBitrate::Create(uint8_t* buffer) const {
+  buffer[0] = kBlockType;
+  buffer[1] = 0;  // Reserved.
+  const size_t block_length_words = (BlockLength() / 4) - 1;
+  ByteWriter<uint16_t>::WriteBigEndian(&buffer[2], block_length_words);
+
+  size_t index = kTargetBitrateHeaderSizeBytes;
+  for (const BitrateItem& item : bitrates_) {
+    buffer[index] = (item.spatial_layer << 4) | item.temporal_layer;
+    ByteWriter<uint32_t, 3>::WriteBigEndian(&buffer[index + 1],
+                                            item.target_bitrate_kbps);
+    index += kBitrateItemSizeBytes;
+  }
+}
+
+bool TargetBitrate::Parse(const uint8_t* block, uint16_t block_length) {
+  if (block_length < 1) {
+    LOG(LS_WARNING)
+        << "Cannot parse TargetBitrate RTCP packet: Too little payload data ("
+        << kTargetBitrateHeaderSizeBytes << " bytes needed, got "
+        << block_length * 4 << ").";
+    return false;
+  }
+
+  // Validate block header (should already have been parsed and checked).
+  RTC_DCHECK_EQ(block[0], kBlockType);
+  RTC_DCHECK_EQ(block_length, ByteReader<uint16_t>::ReadBigEndian(&block[2]));
+
+  // Header specifies block length - 1, but since we ignore the header, which
+  // occupies exactly on block, we can just treat this as payload length.
+  const size_t payload_bytes = block_length * 4;
+  const size_t num_items = payload_bytes / kBitrateItemSizeBytes;
+  size_t index = kTargetBitrateHeaderSizeBytes;
+  bitrates_.clear();
+  for (size_t i = 0; i < num_items; ++i) {
+    uint8_t layers = block[index];
+    uint32_t bitrate_kbps =
+        ByteReader<uint32_t, 3>::ReadBigEndian(&block[index + 1]);
+    index += kBitrateItemSizeBytes;
+    AddTargetBitrate((layers >> 4) & 0x0F, layers & 0x0F, bitrate_kbps);
+  }
+
+  return true;
+}
+
+void TargetBitrate::AddTargetBitrate(uint8_t spatial_layer,
+                                     uint8_t temporal_layer,
+                                     uint32_t target_bitrate_kbps) {
+  RTC_DCHECK_LE(spatial_layer, 0x0F);
+  RTC_DCHECK_LE(temporal_layer, 0x0F);
+  RTC_DCHECK_LE(target_bitrate_kbps, 0x00FFFFFFU);
+  bitrates_.push_back(
+      BitrateItem(spatial_layer, temporal_layer, target_bitrate_kbps));
+}
+
+const std::vector<TargetBitrate::BitrateItem>&
+TargetBitrate::GetTargetBitrates() const {
+  return bitrates_;
+}
+
+size_t TargetBitrate::BlockLength() const {
+  return kTargetBitrateHeaderSizeBytes +
+         bitrates_.size() * kBitrateItemSizeBytes;
+}
+
+}  // namespace rtcp
+}  // namespace webrtc