[rtp_rtcp] rtcp::Remb moved into own file

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

+/*
+ *  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/remb.h"
+
+#include "webrtc/base/logging.h"
+#include "webrtc/modules/rtp_rtcp/source/byte_io.h"
+
+using webrtc::RTCPUtility::PT_PSFB;
+using webrtc::RTCPUtility::RTCPPacketPSFBAPP;
+using webrtc::RTCPUtility::RTCPPacketPSFBREMBItem;
+
+namespace webrtc {
+namespace rtcp {
+namespace {
+const uint32_t kUnusedMediaSourceSsrc0 = 0;
+
+void AssignUWord8(uint8_t* buffer, size_t* offset, uint8_t value) {
+  buffer[(*offset)++] = value;
+}
+
+void AssignUWord32(uint8_t* buffer, size_t* offset, uint32_t value) {
+  ByteWriter<uint32_t>::WriteBigEndian(buffer + *offset, value);
+  *offset += 4;
+}
+
+void ComputeMantissaAnd6bitBase2Exponent(uint32_t input_base10,
+                                         uint8_t bits_mantissa,
+                                         uint32_t* mantissa,
+                                         uint8_t* exp) {
+  // input_base10 = mantissa * 2^exp
+  assert(bits_mantissa <= 32);
+  uint32_t mantissa_max = (1 << bits_mantissa) - 1;
+  uint8_t exponent = 0;
+  for (uint32_t i = 0; i < 64; ++i) {
+    if (input_base10 <= (mantissa_max << i)) {
+      exponent = i;
+      break;
+    }
+  }
+  *exp = exponent;
+  *mantissa = (input_base10 >> exponent);
+}
+
+// Receiver Estimated Max Bitrate (REMB) (draft-alvestrand-rmcat-remb).
+//
+//    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
+//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+//   |V=2|P| FMT=15  |   PT=206      |             length            |
+//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+//   |                  SSRC of packet sender                        |
+//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+//   |                  SSRC of media source                         |
+//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+//   |  Unique identifier 'R' 'E' 'M' 'B'                            |
+//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+//   |  Num SSRC     | BR Exp    |  BR Mantissa                      |
+//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+//   |   SSRC feedback                                               |
+//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+//   |  ...                                                          |
+void CreateRemb(const RTCPPacketPSFBAPP& remb,
+                const RTCPPacketPSFBREMBItem& remb_item,
+                uint8_t* buffer,
+                size_t* pos) {
+  uint32_t mantissa = 0;
+  uint8_t exp = 0;
+  ComputeMantissaAnd6bitBase2Exponent(remb_item.BitRate, 18, &mantissa, &exp);
+
+  AssignUWord32(buffer, pos, remb.SenderSSRC);
+  AssignUWord32(buffer, pos, kUnusedMediaSourceSsrc0);
+  AssignUWord8(buffer, pos, 'R');
+  AssignUWord8(buffer, pos, 'E');
+  AssignUWord8(buffer, pos, 'M');
+  AssignUWord8(buffer, pos, 'B');
+  AssignUWord8(buffer, pos, remb_item.NumberOfSSRCs);
+  AssignUWord8(buffer, pos, (exp << 2) + ((mantissa >> 16) & 0x03));
+  AssignUWord8(buffer, pos, mantissa >> 8);
+  AssignUWord8(buffer, pos, mantissa);
+  for (uint8_t i = 0; i < remb_item.NumberOfSSRCs; ++i) {
+    AssignUWord32(buffer, pos, remb_item.SSRCs[i]);
+  }
+}
+}  // namespace
+
+bool Remb::Create(uint8_t* packet,
+                  size_t* index,
+                  size_t max_length,
+                  RtcpPacket::PacketReadyCallback* callback) const {
+  while (*index + BlockLength() > max_length) {
+    if (!OnBufferFull(packet, index, callback))
+      return false;
+  }
+  const uint8_t kFmt = 15;
+  CreateHeader(kFmt, PT_PSFB, HeaderLength(), packet, index);
+  CreateRemb(remb_, remb_item_, packet, index);
+  return true;
+}
+
+void Remb::AppliesTo(uint32_t ssrc) {
+  if (remb_item_.NumberOfSSRCs >= kMaxNumberOfSsrcs) {
+    LOG(LS_WARNING) << "Max number of REMB feedback SSRCs reached.";
+    return;
+  }
+  remb_item_.SSRCs[remb_item_.NumberOfSSRCs++] = ssrc;
+}
+
+}  // namespace rtcp
+}  // namespace webrtc