h.264 SODB RBSP EBSP的區別

本文轉載自http://blog.csdn.net/threewells_14/article/details/1508657

SODB　數據比特串－－＞最原始的編碼數據

RBSP　原始字節序列載荷－－＞在SODB的後面填加了結尾比特（RBSP trailing bits　一個bit“1”）若干比特“0”,以便字節對齊。

EBSP　擴展字節序列載荷-->在RBSP基礎上填加了仿校驗字節（0X03）它的原因是：　在NALU加到Annexb上時，需要填加每組NALU之前的開始碼StartCodePrefix,如果該NALU對應的slice爲一幀的開始則用4位字節表示，ox00000001,否則用3位字節表示ox000001.爲了使NALU主體中不包括與開始碼相沖突的，在編碼時，每遇到兩個字節連續爲0，就插入一個字節的0x03。解碼時將0x03去掉。也稱爲脫殼操作。

 

網上查詢的區別：

在對整幀圖像的數據比特串(SODB)添加原始字節序列載荷(RBSP)結尾比特(RBSP trailing bits,添加一比特的“1”和若干比特“0”,以便字節對齊)後,再檢查RBSP 中是否存在連續的三字節“00000000 00000000 000000xx”;若存在這種連續的三字節碼,在第三字節前插入一字節的“0×03”,以免與起始碼競爭,形成EBSP碼流,這需要將近兩倍的整幀圖像碼流大小。爲了減小存儲器需求,在每個宏塊編碼結束後即檢查該宏塊SODB中的起始碼競爭問題,並保留SODB最後兩字節的零字節個數,以便與下一宏塊的SODB的開始字節形成連續的起始碼競爭檢測;對一幀圖像的最後一個宏塊,先添加結尾停止比特,再檢測起始碼競爭。

 

程序：

typedef struct

{

  int             byte_pos;           //!< current position in bitstream;

  int             bits_to_go;         //!< current bitcounter

  byte            byte_buf;           //!< current buffer for last written byte

  int             stored_byte_pos;    //!< storage for position in bitstream;

  int             stored_bits_to_go;  //!< storage for bitcounter

  byte            stored_byte_buf;    //!< storage for buffer of last written byte

 

  byte            byte_buf_skip;      //!< current buffer for last written byte

  int             byte_pos_skip;      //!< storage for position in bitstream;

  int             bits_to_go_skip;    //!< storage for bitcounter

 

  byte            *streamBuffer;      //!< actual buffer for written bytes

  int             write_flag;         //!< Bitstream contains data and needs to be written

 

} Bitstream;　定義比特流結構

 

 

static byte *NAL_Payload_buffer;

void SODBtoRBSP(Bitstream *currStream)
{
  currStream->byte_buf <<= 1;　　//左移1bit
  currStream->byte_buf |= 1;　　　//在尾部填一個“1”佔1bit
  currStream->bits_to_go--;
  currStream->byte_buf <<= currStream->bits_to_go;
  currStream->streamBuffer[currStream->byte_pos++] = currStream->byte_buf;
  currStream->bits_to_go = 8;
  currStream->byte_buf = 0;
}

 

 

int RBSPtoEBSP(byte *streamBuffer, int begin_bytepos, int end_bytepos, int min_num_bytes)
{
  
  int i, j, count;

  for(i = begin_bytepos; i < end_bytepos; i++)
    NAL_Payload_buffer[i] = streamBuffer[i];

  count = 0;
  j = begin_bytepos;
  for(i = begin_bytepos; i < end_bytepos; i++) 
  {
    if(count == ZEROBYTES_SHORTSTARTCODE && !(NAL_Payload_buffer[i] & 0xFC)) 
    {
      streamBuffer[j] = 0x03;
      j++;
      count = 0;   
    }
    streamBuffer[j] = NAL_Payload_buffer[i];
    if(NAL_Payload_buffer[i] == 0x00)      
      count++;
    else 
      count = 0;
    j++;
  }
  while (j < begin_bytepos+min_num_bytes) {
    streamBuffer[j] = 0x00; // cabac stuffing word
    streamBuffer[j+1] = 0x00;
    streamBuffer[j+2] = 0x03;
    j += 3;
    stat->bit_use_stuffingBits[img->type]+=16;
  }
  return j;
}