NALwrite.cpp

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#include <vector>
#include <algorithm>
#include <ostream>

#include "CommonLib/NAL.h"
#include "CommonLib/BitStream.h"
#include "NALwrite.h"

//! \ingroup EncoderLib
//! \{

static const uint8_t emulation_prevention_three_byte = 3;

void writeNalUnitHeader(std::ostream &out, OutputNALUnit &nalu)   // nal_unit_header()
{
  OutputBitstream bsNALUHeader;
  int forbiddenZero = 0;
  bsNALUHeader.write(forbiddenZero, 1);   // forbidden_zero_bit
  int nuhReservedZeroBit = 0;
  bsNALUHeader.write(nuhReservedZeroBit, 1);   // nuh_reserved_zero_bit
  CHECK(nalu.m_nuhLayerId > 55, "The value of nuh_layer_id shall be in the range of 0 to 55, inclusive");
  bsNALUHeader.write(nalu.m_nuhLayerId, 6);       // nuh_layer_id
  bsNALUHeader.write(nalu.m_nalUnitType, 5);      // nal_unit_type
  bsNALUHeader.write(nalu.m_temporalId + 1, 3);   // nuh_temporal_id_plus1

  out.write(reinterpret_cast<const char*>(bsNALUHeader.getByteStream()), bsNALUHeader.getByteStreamLength());
}

/**
 * write nalu to bytestream out, performing RBSP anti startcode
 * emulation as required.  nalu.m_RBSPayload must be byte aligned.
 */
void writeNaluContent(std::ostream &out, OutputNALUnit &nalu)
{
  /* write out rsbp_byte's, inserting any required
   * emulation_prevention_three_byte's */
  /* 7.4.1 ...
   * emulation_prevention_three_byte is a byte equal to 0x03. When an
   * emulation_prevention_three_byte is present in the NAL unit, it shall be
   * discarded by the decoding process.
   * The last byte of the NAL unit shall not be equal to 0x00.
   * Within the NAL unit, the following three-byte sequences shall not occur at
   * any byte-aligned position:
   *  - 0x000000
   *  - 0x000001
   *  - 0x000002
   * Within the NAL unit, any four-byte sequence that starts with 0x000003
   * other than the following sequences shall not occur at any byte-aligned
   * position:
   *  - 0x00000300
   *  - 0x00000301
   *  - 0x00000302
   *  - 0x00000303
   */
  std::vector<uint8_t> &rbsp = nalu.m_bitstream.getFifo();

  std::vector<uint8_t> outputBuffer;
  outputBuffer.resize(rbsp.size()*2+1); //there can never be enough emulation_prevention_three_bytes to require this much space
  std::size_t outputAmount = 0;
  int         zeroCount    = 0;
  for (std::vector<uint8_t>::iterator it = rbsp.begin(); it != rbsp.end(); it++)
  {
    const uint8_t v=(*it);
    if (zeroCount==2 && v<=3)
    {
      outputBuffer[outputAmount++]=emulation_prevention_three_byte;
      zeroCount=0;
    }

    if (v==0)
    {
      zeroCount++;
    }
    else
    {
      zeroCount=0;
    }
    outputBuffer[outputAmount++]=v;
  }

  /* 7.4.1.1
   * ... when the last byte of the RBSP data is equal to 0x00 (which can
   * only occur when the RBSP ends in a cabac_zero_word), a final byte equal
   * to 0x03 is appended to the end of the data.
   */
  if (zeroCount>0)
  {
    outputBuffer[outputAmount++]=emulation_prevention_three_byte;
  }
  out.write(reinterpret_cast<const char*>(&(*outputBuffer.begin())), outputAmount);
}

void writeNaluWithHeader(std::ostream &out, OutputNALUnit &nalu)
{
  writeNalUnitHeader(out, nalu);
  writeNaluContent(out, nalu);
}

//! \}