root/media/cast/rtp_receiver/rtp_parser/rtp_parser.cc

DEFINITIONS

1. ParsePacket
2. ParseCommon
3. ParseCast

// Copyright 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "media/cast/rtp_receiver/rtp_parser/rtp_parser.h"

#include "base/big_endian.h"
#include "base/logging.h"
#include "media/cast/cast_defines.h"
#include "media/cast/rtp_receiver/rtp_receiver.h"

namespace media {
namespace cast {

static const size_t kRtpCommonHeaderLength = 12;
static const size_t kRtpCastHeaderLength = 7;
static const uint8 kCastKeyFrameBitMask = 0x80;
static const uint8 kCastReferenceFrameIdBitMask = 0x40;

RtpParser::RtpParser(const RtpParserConfig parser_config)
    : parser_config_(parser_config) {}

RtpParser::~RtpParser() {}

bool RtpParser::ParsePacket(const uint8* packet,
                            size_t length,
                            RtpCastHeader* rtp_header) {
  if (length == 0)
    return false;
  // Get RTP general header.
  if (!ParseCommon(packet, length, rtp_header))
    return false;
  if (rtp_header->webrtc.header.payloadType == parser_config_.payload_type &&
      rtp_header->webrtc.header.ssrc == parser_config_.ssrc) {
    return ParseCast(packet + kRtpCommonHeaderLength,
                     length - kRtpCommonHeaderLength,
                     rtp_header);
  }
  // Not a valid payload type / ssrc combination.
  return false;
}

bool RtpParser::ParseCommon(const uint8* packet,
                            size_t length,
                            RtpCastHeader* rtp_header) {
  if (length < kRtpCommonHeaderLength)
    return false;
  uint8 version = packet[0] >> 6;
  if (version != 2)
    return false;
  uint8 cc = packet[0] & 0x0f;
  bool marker = ((packet[1] & 0x80) != 0);
  int payload_type = packet[1] & 0x7f;

  uint16 sequence_number;
  uint32 rtp_timestamp, ssrc;
  base::BigEndianReader big_endian_reader(
      reinterpret_cast<const char*>(packet + 2), 10);
  big_endian_reader.ReadU16(&sequence_number);
  big_endian_reader.ReadU32(&rtp_timestamp);
  big_endian_reader.ReadU32(&ssrc);

  if (ssrc != parser_config_.ssrc)
    return false;

  rtp_header->webrtc.header.markerBit = marker;
  rtp_header->webrtc.header.payloadType = payload_type;
  rtp_header->webrtc.header.sequenceNumber = sequence_number;
  rtp_header->webrtc.header.timestamp = rtp_timestamp;
  rtp_header->webrtc.header.ssrc = ssrc;
  rtp_header->webrtc.header.numCSRCs = cc;

  uint8 csrc_octs = cc * 4;
  rtp_header->webrtc.type.Audio.numEnergy = rtp_header->webrtc.header.numCSRCs;
  rtp_header->webrtc.header.headerLength = kRtpCommonHeaderLength + csrc_octs;
  rtp_header->webrtc.type.Audio.isCNG = false;
  rtp_header->webrtc.type.Audio.channel = parser_config_.audio_channels;
  // TODO(pwestin): look at x bit and skip data.
  return true;
}

bool RtpParser::ParseCast(const uint8* packet,
                          size_t length,
                          RtpCastHeader* rtp_header) {
  if (length < kRtpCastHeaderLength)
    return false;

  // Extract header.
  const uint8* data_ptr = packet;
  size_t data_length = length;
  rtp_header->is_key_frame = !!(data_ptr[0] & kCastKeyFrameBitMask);
  rtp_header->is_reference = !!(data_ptr[0] & kCastReferenceFrameIdBitMask);
  rtp_header->frame_id = frame_id_wrap_helper_.MapTo32bitsFrameId(data_ptr[1]);

  base::BigEndianReader big_endian_reader(
      reinterpret_cast<const char*>(data_ptr + 2), 4);
  big_endian_reader.ReadU16(&rtp_header->packet_id);
  big_endian_reader.ReadU16(&rtp_header->max_packet_id);

  if (rtp_header->is_reference) {
    rtp_header->reference_frame_id =
        reference_frame_id_wrap_helper_.MapTo32bitsFrameId(data_ptr[6]);
    data_ptr += kRtpCastHeaderLength;
    data_length -= kRtpCastHeaderLength;
  } else {
    data_ptr += kRtpCastHeaderLength - 1;
    data_length -= kRtpCastHeaderLength - 1;
  }

  if (rtp_header->max_packet_id < rtp_header->packet_id)
    return false;

  OnReceivedPayloadData(data_ptr, data_length, *rtp_header);
  return true;
}

}  // namespace cast
}  // namespace media