vlc.c

H.264基于baseline解码器的C++实现源码

#endif

  return retval;
}

/*!
 ************************************************************************
 * \brief
 *    read Level VLC0 codeword from UVLC-partition
 ************************************************************************
 */
int readSyntaxElement_Level_VLC0(SyntaxElement *sym, Bitstream *currStream)
{
  int frame_bitoffset        = currStream->frame_bitoffset;
  int BitstreamLengthInBytes = currStream->bitstream_length;
  int BitstreamLengthInBits  = (BitstreamLengthInBytes << 3) + 7;
  byte *buf                  = currStream->streamBuffer;
  int len = 1, sign = 0, level = 0, code = 1;

  while (!ShowBits(buf, frame_bitoffset++, BitstreamLengthInBits, 1))
    len++;

  if (len < 15)
  {
    sign  = (len - 1) & 1;
    level = ((len - 1) >> 1) + 1;
  }
  else if (len == 15)
  {
    // escape code
    code <<= 4;
    code |= ShowBits(buf, frame_bitoffset, BitstreamLengthInBits, 4);
    len  += 4;
    frame_bitoffset += 4;
    sign = (code & 0x01);
    level = ((code >> 1) & 0x07) + 8;
  }
  else if (len >= 16)
  {
    // escape code
    int addbit = (len - 16);
    int offset = (2048 << addbit) - 2032;
    len   -= 4;
    code   = ShowBits(buf, frame_bitoffset, BitstreamLengthInBits, len);
    sign   = (code & 0x01);
    frame_bitoffset += len;    
    level = (code >> 1) + offset;

    code |= (1 << (len)); // for display purpose only
    len += addbit + 16;
 }

  sym->inf = (sign) ? -level : level ;
  sym->len = len;

#if TRACE
  tracebits2(sym->tracestring, sym->len, code);
#endif

  currStream->frame_bitoffset = frame_bitoffset;
  return 0;
}

/*!
 ************************************************************************
 * \brief
 *    read Level VLC codeword from UVLC-partition
 ************************************************************************
 */
int readSyntaxElement_Level_VLCN(SyntaxElement *sym, int vlc, Bitstream *currStream)
{
  int frame_bitoffset        = currStream->frame_bitoffset;
  int BitstreamLengthInBytes = currStream->bitstream_length;
  int BitstreamLengthInBits  = (BitstreamLengthInBytes << 3) + 7;
  byte *buf                  = currStream->streamBuffer;

  int levabs, sign;
  int len = 1;
  int code = 1, sb;

  int shift = vlc - 1;

  // read pre zeros
  while (!ShowBits(buf, frame_bitoffset ++, BitstreamLengthInBits, 1))
    len++;

  frame_bitoffset -= len;

  if (len < 16)
  {
    levabs = ((len - 1) << shift) + 1;

    // read (vlc-1) bits -> suffix
    if (shift)
    {
      sb =  ShowBits(buf, frame_bitoffset + len, BitstreamLengthInBits, shift);
      code = (code << (shift) )| sb;
      levabs += sb;
      len += (shift);
    }

    // read 1 bit -> sign
    sign = ShowBits(buf, frame_bitoffset + len, BitstreamLengthInBits, 1);
    code = (code << 1)| sign;
    len ++;
  }
  else // escape
  {
    int addbit = len - 5;
    int offset = (1 << addbit) + (15 << shift) - 2047;

    sb = ShowBits(buf, frame_bitoffset + len, BitstreamLengthInBits, addbit);
    code = (code << addbit ) | sb;
    len   += addbit;

    levabs = sb + offset;
    
    // read 1 bit -> sign
    sign = ShowBits(buf, frame_bitoffset + len, BitstreamLengthInBits, 1);

    code = (code << 1)| sign;

    len++;
  }

  sym->inf = (sign)? -levabs : levabs;
  sym->len = len;

  currStream->frame_bitoffset = frame_bitoffset + len;

#if TRACE
  tracebits2(sym->tracestring, sym->len, code);
#endif

  return 0;
}

/*!
 ************************************************************************
 * \brief
 *    read Total Zeros codeword from UVLC-partition
 ************************************************************************
 */
int readSyntaxElement_TotalZeros(SyntaxElement *sym,  Bitstream *currStream)
{
  static const byte lentab[TOTRUN_NUM][16] =
  {

    { 1,3,3,4,4,5,5,6,6,7,7,8,8,9,9,9},
    { 3,3,3,3,3,4,4,4,4,5,5,6,6,6,6},
    { 4,3,3,3,4,4,3,3,4,5,5,6,5,6},
    { 5,3,4,4,3,3,3,4,3,4,5,5,5},
    { 4,4,4,3,3,3,3,3,4,5,4,5},
    { 6,5,3,3,3,3,3,3,4,3,6},
    { 6,5,3,3,3,2,3,4,3,6},
    { 6,4,5,3,2,2,3,3,6},
    { 6,6,4,2,2,3,2,5},
    { 5,5,3,2,2,2,4},
    { 4,4,3,3,1,3},
    { 4,4,2,1,3},
    { 3,3,1,2},
    { 2,2,1},
    { 1,1},
  };

  static const byte codtab[TOTRUN_NUM][16] =
  {
    {1,3,2,3,2,3,2,3,2,3,2,3,2,3,2,1},
    {7,6,5,4,3,5,4,3,2,3,2,3,2,1,0},
    {5,7,6,5,4,3,4,3,2,3,2,1,1,0},
    {3,7,5,4,6,5,4,3,3,2,2,1,0},
    {5,4,3,7,6,5,4,3,2,1,1,0},
    {1,1,7,6,5,4,3,2,1,1,0},
    {1,1,5,4,3,3,2,1,1,0},
    {1,1,1,3,3,2,2,1,0},
    {1,0,1,3,2,1,1,1,},
    {1,0,1,3,2,1,1,},
    {0,1,1,2,1,3},
    {0,1,1,1,1},
    {0,1,1,1},
    {0,1,1},
    {0,1},
  };

  int code;
  int vlcnum = sym->value1;
  int retval = code_from_bitstream_2d(sym, currStream, &lentab[vlcnum][0], &codtab[vlcnum][0], 16, 1, &code);

  if (retval)
  {
    printf("ERROR: failed to find Total Zeros !cdc\n");
    exit(-1);
  }

#if TRACE
  tracebits2(sym->tracestring, sym->len, code);
#endif

  return retval;
}

/*!
 ************************************************************************
 * \brief
 *    read Total Zeros Chroma DC codeword from UVLC-partition
 ************************************************************************
 */
int readSyntaxElement_TotalZerosChromaDC(SyntaxElement *sym,  Bitstream *currStream)
{
  static const byte lentab[3][TOTRUN_NUM][16] =
  {
    //YUV420
   {{ 1,2,3,3},
    { 1,2,2},
    { 1,1}},
    //YUV422
   {{ 1,3,3,4,4,4,5,5},
    { 3,2,3,3,3,3,3},
    { 3,3,2,2,3,3},
    { 3,2,2,2,3},
    { 2,2,2,2},
    { 2,2,1},
    { 1,1}},
    //YUV444
   {{ 1,3,3,4,4,5,5,6,6,7,7,8,8,9,9,9},
    { 3,3,3,3,3,4,4,4,4,5,5,6,6,6,6},
    { 4,3,3,3,4,4,3,3,4,5,5,6,5,6},
    { 5,3,4,4,3,3,3,4,3,4,5,5,5},
    { 4,4,4,3,3,3,3,3,4,5,4,5},
    { 6,5,3,3,3,3,3,3,4,3,6},
    { 6,5,3,3,3,2,3,4,3,6},
    { 6,4,5,3,2,2,3,3,6},
    { 6,6,4,2,2,3,2,5},
    { 5,5,3,2,2,2,4},
    { 4,4,3,3,1,3},
    { 4,4,2,1,3},
    { 3,3,1,2},
    { 2,2,1},
    { 1,1}}
  };

  static const byte codtab[3][TOTRUN_NUM][16] =
  {
    //YUV420
   {{ 1,1,1,0},
    { 1,1,0},
    { 1,0}},
    //YUV422
   {{ 1,2,3,2,3,1,1,0},
    { 0,1,1,4,5,6,7},
    { 0,1,1,2,6,7},
    { 6,0,1,2,7},
    { 0,1,2,3},
    { 0,1,1},
    { 0,1}},
    //YUV444
   {{1,3,2,3,2,3,2,3,2,3,2,3,2,3,2,1},
    {7,6,5,4,3,5,4,3,2,3,2,3,2,1,0},
    {5,7,6,5,4,3,4,3,2,3,2,1,1,0},
    {3,7,5,4,6,5,4,3,3,2,2,1,0},
    {5,4,3,7,6,5,4,3,2,1,1,0},
    {1,1,7,6,5,4,3,2,1,1,0},
    {1,1,5,4,3,3,2,1,1,0},
    {1,1,1,3,3,2,2,1,0},
    {1,0,1,3,2,1,1,1,},
    {1,0,1,3,2,1,1,},
    {0,1,1,2,1,3},
    {0,1,1,1,1},
    {0,1,1,1},
    {0,1,1},
    {0,1}}
  };

  int code;
  int yuv = active_sps->chroma_format_idc - 1;
  int vlcnum = sym->value1;
  int retval = code_from_bitstream_2d(sym, currStream, &lentab[yuv][vlcnum][0], &codtab[yuv][vlcnum][0], 16, 1, &code);

  if (retval)
  {
    printf("ERROR: failed to find Total Zeros\n");
    exit(-1);
  }

#if TRACE
  tracebits2(sym->tracestring, sym->len, code);
#endif

  return retval;
}


/*!
 ************************************************************************
 * \brief
 *    read  Run codeword from UVLC-partition
 ************************************************************************
 */
int readSyntaxElement_Run(SyntaxElement *sym, Bitstream *currStream)
{
  static const byte lentab[TOTRUN_NUM][16] =
  {
    {1,1},
    {1,2,2},
    {2,2,2,2},
    {2,2,2,3,3},
    {2,2,3,3,3,3},
    {2,3,3,3,3,3,3},
    {3,3,3,3,3,3,3,4,5,6,7,8,9,10,11},
  };

  static const byte codtab[TOTRUN_NUM][16] =
  {
    {1,0},
    {1,1,0},
    {3,2,1,0},
    {3,2,1,1,0},
    {3,2,3,2,1,0},
    {3,0,1,3,2,5,4},
    {7,6,5,4,3,2,1,1,1,1,1,1,1,1,1},
  };
  int code;
  int vlcnum = sym->value1;
  int retval = code_from_bitstream_2d(sym, currStream, &lentab[vlcnum][0], &codtab[vlcnum][0], 16, 1, &code);

  if (retval)
  {
    printf("ERROR: failed to find Run\n");
    exit(-1);
  }

#if TRACE
  tracebits2(sym->tracestring, sym->len, code);
#endif

  return retval;
}


/*!
 ************************************************************************
 * \brief
 *  Reads bits from the bitstream buffer
 *
 * \param buffer
 *    containing VLC-coded data bits
 * \param totbitoffset
 *    bit offset from start of partition
 * \param info
 *    returns value of the read bits
 * \param bitcount
 *    total bytes in bitstream
 * \param numbits
 *    number of bits to read
 *
 ************************************************************************
 */
int GetBits (byte buffer[],int totbitoffset,int *info, int bitcount,
             int numbits)
{
  if ((totbitoffset + numbits ) > bitcount) 
  {
    return -1;
  }
  else
  {
    int bitoffset  = 7 - (totbitoffset & 0x07); // bit from start of byte
    int byteoffset = (totbitoffset >> 3); // byte from start of buffer
    int bitcounter = numbits;
    byte *curbyte  = &(buffer[byteoffset]);
    int inf = 0;

    while (numbits--)
    {
      inf <<=1;    
      inf |= ((*curbyte)>> (bitoffset--)) & 0x01;    
      if (bitoffset == -1 ) 
      { //Move onto next byte to get all of numbits
        curbyte++;
        bitoffset = 7;
      }
      // Above conditional could also be avoided using the following:
      // curbyte   -= (bitoffset >> 3);
      // bitoffset &= 0x07;
    }
    *info = inf;

    return bitcounter;           // return absolute offset in bit from start of frame
  }
}

/*!
 ************************************************************************
 * \brief
 *  Reads bits from the bitstream buffer
 *
 * \param buffer
 *    buffer containing VLC-coded data bits
 * \param totbitoffset
 *    bit offset from start of partition
 * \param bitcount
 *    total bytes in bitstream
 * \param numbits
 *    number of bits to read
 *
 ************************************************************************
 */

int ShowBits (byte buffer[],int totbitoffset,int bitcount, int numbits)
{
  if ((totbitoffset + numbits )  > bitcount) 
  {
    return -1;
  }
  else
  {
    int bitoffset  = 7 - (totbitoffset & 0x07); // bit from start of byte
    int byteoffset = (totbitoffset >> 3); // byte from start of buffer
    byte *curbyte  = &(buffer[byteoffset]);
    int inf        = 0;

    while (numbits--)
    {
      inf <<=1;    
      inf |= ((*curbyte)>> (bitoffset--)) & 0x01;

      if (bitoffset == -1 ) 
      { //Move onto next byte to get all of numbits
        curbyte++;
        bitoffset = 7;
      }
    }
    return inf;           // return absolute offset in bit from start of frame
  }
}