1、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
完成兩件事:1、在原始數據流後加1位1;2、如果當前數據流位數不足一字節8位,則補零
void SODBtoRBSP(Bitstream *currStream)
currStream->byte_buf <<= 1;
currStream->byte_buf |= 1; //在當前字符流後加一個1 1bit
currStream->bits_to_go--; //剩下幾bit以組成一字節
currStream->byte_buf <<= currStream->bits_to_go;
currStream->streamBuffer[currStream->byte_pos++] = currStream->byte_buf; //在buff中添加一個字節以保存當前字符流
currStream->bits_to_go = 8;
currStream->byte_buf = 0;
}
2、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,需要添加每組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。
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)) //0xFC-->0x1111 1100 取前3個字節
{
streamBuffer[j] = 0x03;//在最後一個字節前添加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;
}