//这个函数输入为一个NAL结构体，主要功能为得到一个完整的NALU并保存在NALU_t的buf中，
//获取他的长度，填充F,IDC,TYPE位。
//并且返回两个开始字符之间间隔的字节数，即包含有前缀的NALU的长度
int GetAnnexbNALU (sp<ABuffer> nalu)
{
int pos = 0;
int StartCodeFound, rewind;
// unsigned char *Buf;
int info2,info3,startcodeprefix_len,len;
static unsigned char Buf[50000];
startcodeprefix_len=3;//初始化码流序列的开始字符为3个字节
if (3 != fread (Buf, 1, 3, bits))//从码流中读3个字节
{
//free(Buf);
return 0;
}
info2 = FindStartCode2 (Buf);//判断是否为0x000001
if(info2 != 1)
{
//如果不是，再读一个字节
if(1 != fread(Buf+3, 1, 1, bits))//读一个字节
{
//free(Buf);
return 0;
}
info3 = FindStartCode3 (Buf);//判断是否为0x00000001
if (info3 != 1)//如果不是，返回-1
{
//free(Buf);
return -1;
}
else
{
//如果是0x00000001,得到开始前缀为4个字节
pos = 4;
startcodeprefix_len = 4;
}
}
else
{
//如果是0x000001,得到开始前缀为3个字节
startcodeprefix_len = 3;
pos = 3;
}
//查找下一个开始字符的标志位
StartCodeFound = 0;
info2 = 0;
info3 = 0;
while (!StartCodeFound)
{
if (feof (bits))//判断是否到了文件尾
{
//return 0;
len = (pos-1)- startcodeprefix_len;
memcpy (nalu->data(), &Buf[startcodeprefix_len], len);
//free(Buf);
printf("lcy 1991 len %d\n",len);
return pos-1;
}
Buf[pos++] = fgetc (bits);//读一个字节到BUF中
info3 = FindStartCode3(&Buf[pos-4]);//判断是否为0x00000001
if(info3 != 1)
info2 = FindStartCode2(&Buf[pos-3]);//判断是否为0x000001
StartCodeFound = (info2 == 1 || info3 == 1);
}
// Here, we have found another start code (and read length of startcode bytes more than we should
// have. Hence, go back in the file
rewind = (info3 == 1)? -4 : -3;
if (0 != fseek (bits, rewind, SEEK_CUR))//把文件指针指向前一个NALU的末尾
{
//free(Buf);
printf("GetAnnexbNALU: Cannot fseek in the bit stream file");
}
// Here the Start code, the complete NALU, and the next start code is in the Buf.
// The size of Buf is pos, pos+rewind are the number of bytes excluding the next
// start code, and (pos+rewind)-startcodeprefix_len is the size of the NALU excluding the start code
len = (pos+rewind)-startcodeprefix_len;
memcpy (nalu->data(), &Buf[startcodeprefix_len], len);//拷贝一个完整NALU，不拷贝起始前缀0x000001或0x00000001
//free(Buf);
printf("memcpy2\n");
return (pos+rewind);//返回两个开始字符之间间隔的字节数，即包含有前缀的NALU的长度
}
//这个函数输入为一个NAL结构体，主要功能为得到一个完整的NALU并保存在NALU_t的buf中，获取他的长度，填充F,IDC,TYPE位。
//并且返回两个开始字符之间间隔的字节数，即包含有前缀的NALU的长度
int GetAnnexbNALU (NALU_t *nalu)
{
int pos = 0;
int StartCodeFound, rewind;
unsigned char *Buf;
if ((Buf = (unsigned char*)calloc (nalu->max_size , sizeof(char))) == NULL)
printf ("GetAnnexbNALU: Could not allocate Buf memory\n");
nalu->startcodeprefix_len=3;//初始化码流序列的开始字符为3个字节
if (3 != fread (Buf, 1, 3, bits))//从码流中读3个字节
{
free(Buf);
return 0;
}
info2 = FindStartCode2 (Buf);//判断是否为0x000001
if(info2 != 1)
{
//如果不是，再读一个字节
if(1 != fread(Buf+3, 1, 1, bits))//读一个字节
{
free(Buf);
return 0;
}
info3 = FindStartCode3 (Buf);//判断是否为0x00000001
if (info3 != 1)//如果不是，返回-1
{
free(Buf);
return -1;
}
else
{
//如果是0x00000001,得到开始前缀为4个字节
pos = 4;
nalu->startcodeprefix_len = 4;
}
}
else
{
//如果是0x000001,得到开始前缀为3个字节
nalu->startcodeprefix_len = 3;
pos = 3;
}
//查找下一个开始字符的标志位
StartCodeFound = 0;
info2 = 0;
info3 = 0;
while (!StartCodeFound)
{
if (feof (bits))//判断是否到了文件尾
{
nalu->len = (pos-1)-nalu->startcodeprefix_len;
memcpy (nalu->buf, &Buf[nalu->startcodeprefix_len], nalu->len);
nalu->forbidden_bit = nalu->buf[0] & 0x80; //1 bit
nalu->nal_reference_idc = nalu->buf[0] & 0x60; // 2 bit
nalu->nal_unit_type = (nalu->buf[0]) & 0x1f;// 5 bit
free(Buf);
return pos-1;
}
Buf[pos++] = fgetc (bits);//读一个字节到BUF中
info3 = FindStartCode3(&Buf[pos-4]);//判断是否为0x00000001
if(info3 != 1)
info2 = FindStartCode2(&Buf[pos-3]);//判断是否为0x000001
StartCodeFound = (info2 == 1 || info3 == 1);
}
// Here, we have found another start code (and read length of startcode bytes more than we should
// have. Hence, go back in the file
rewind = (info3 == 1)? -4 : -3;
if (0 != fseek (bits, rewind, SEEK_CUR))//把文件指针指向前一个NALU的末尾
{
free(Buf);
printf("GetAnnexbNALU: Cannot fseek in the bit stream file");
}
// Here the Start code, the complete NALU, and the next start code is in the Buf.
// The size of Buf is pos, pos+rewind are the number of bytes excluding the next
// start code, and (pos+rewind)-startcodeprefix_len is the size of the NALU excluding the start code
nalu->len = (pos+rewind)-nalu->startcodeprefix_len;
memcpy (nalu->buf, &Buf[nalu->startcodeprefix_len], nalu->len);//拷贝一个完整NALU，不拷贝起始前缀0x000001或0x00000001
nalu->forbidden_bit = nalu->buf[0] & 0x80; //1 bit
nalu->nal_reference_idc = nalu->buf[0] & 0x60; // 2 bit
nalu->nal_unit_type = (nalu->buf[0]) & 0x1f;// 5 bit
free(Buf);
return (pos+rewind);//返回两个开始字符之间间隔的字节数，即包含有前缀的NALU的长度
}
