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H264的NALU提取

1、nalu单元

定义nalu的存储单元，ebsp用来存储原始的包含起始码（annexb格式）的原始码流，sodb存储去除防竞争字节后的码流，prefix是3或4字节

nalu_def.h

// nalu_def.h
#pragma once#include <cstdint>class Nalu
{
public:uint8_t* ebsp;uint32_t ebsp_len;uint8_t* sodb;uint32_t sodb_len;uint8_t prefix;uint8_t forbidden_zero_bit;	// 1 bituint8_t nal_ref_idc;		// 2 bitsuint8_t nal_unit_type;		// 5 bitsNalu();Nalu(uint8_t* stream, uint32_t len);~Nalu();void Init(uint8_t* stream, uint32_t len);int ParsePrefix();int ParseRBSP();int ParseHead();uint8_t GetNalUnitType();uint8_t* GetEBSP();uint8_t* GetRBSP();uint8_t* GetSODB();uint32_t GetLenthEBSP();uint32_t GetLenthRBSP();uint32_t GetLenthSODB();};

nalu_def.c

#include <string.h>
#include "nalu_def.h"Nalu::Nalu():ebsp(NULL),ebsp_len(0),sodb(NULL),sodb_len(0),prefix(0),forbidden_zero_bit(0),nal_ref_idc(0),nal_unit_type(0)
{
}Nalu::Nalu(uint8_t* stream, uint32_t len):Nalu()
{Init(stream, len);
}Nalu::~Nalu()
{if (ebsp){delete[] ebsp;}if (sodb){delete[] sodb;}
}void Nalu::Init(uint8_t* stream, uint32_t len)
{if (ebsp){delete[] ebsp;}ebsp = new uint8_t[len];ebsp_len = len;memcpy(ebsp, stream, len);
}int Nalu::ParsePrefix()
{prefix = 0;if (ebsp_len <= 3){if (ebsp[0] == 0 && ebsp[1] == 0 && ebsp[2] == 1)prefix = 3;}else{if (ebsp[0] == 0 && ebsp[1] == 0 && ebsp[2] == 1)prefix = 3;else if (ebsp[0] == 0 && ebsp[1] == 0 && ebsp[2] == 0 && ebsp[3] == 1)prefix = 4;}return prefix == 0 ? -1 : 0;
}int Nalu::ParseRBSP()
{if (ebsp_len < prefix)return -1;if(sodb){delete[] ebsp;}sodb = new uint8_t[ebsp_len];sodb_len = ebsp_len;uint8_t* src = ebsp + prefix;uint8_t* end = ebsp + ebsp_len;uint8_t* dest_temp = sodb;while (src < end){if (src < end - 3 &&(0x00 == src[0] && 0x00 == src[1] && 0x03 == src[2])){*dest_temp++ = 0x00;*dest_temp++ = 0x00;src += 3;continue;}*dest_temp++ = *src++;}sodb_len = dest_temp - sodb;return 0;
}int Nalu::ParseHead()
{if (ebsp_len < prefix + 1)return -1;uint8_t* head = ebsp + prefix;forbidden_zero_bit = (head[0] >> 7) & 0x1;nal_ref_idc = (head[0] >> 5) & 0x3;nal_unit_type = head[0] & 0x1f;return 0;
}uint8_t Nalu::GetNalUnitType()
{return nal_unit_type;
}uint8_t* Nalu::GetEBSP()
{return ebsp;
}uint8_t* Nalu::GetRBSP()
{return ebsp + prefix;
}uint8_t* Nalu::GetSODB()
{return sodb;
}uint32_t Nalu::GetLenthEBSP()
{return ebsp_len;
}uint32_t Nalu::GetLenthRBSP()
{return ebsp_len - prefix;
}uint32_t Nalu::GetLenthSODB()
{return sodb_len;
}

2、nalu文件读取器

每次读取BUFF_SIZE个字节数据到缓冲区中，分割成nalu单元后存入队列，队列为空时加载数据再次存入缓冲区中进行分割

nalu_file_reader.h

#pragma once#include <cstdio>
#include <queue>
#include "nalu_def.h"class NaluFileReader
{
public:NaluFileReader();~NaluFileReader();bool OpenFile(const char* path);Nalu* GetNalu();void CloseFile();private:uint8_t _status;FILE* _file;uint8_t* _buffer;uint32_t _size;std::queue<Nalu*> _nalus;const int32_t BUFF_SIZE = 128 * 1024;void ReadFromFile();int32_t FindStartCode(const uint8_t* buf, uint32_t size, uint8_t* prefix);int Splite();
};

nalu_file_reader.c

#include "nalu_file_reader.h"#pragma warning(disable:4996)NaluFileReader::NaluFileReader() :_status(0),_file(NULL),_buffer(NULL),_size(0)
{_buffer = new uint8_t[BUFF_SIZE];
}NaluFileReader::~NaluFileReader()
{delete[] _buffer;while (!_nalus.empty()){auto nal = _nalus.front();_nalus.pop();delete nal;}
}bool NaluFileReader::OpenFile(const char* path)
{fopen_s(&_file, path, "rb");_status = 0;return _file ? true : false;
}Nalu* NaluFileReader::GetNalu()
{if (!_nalus.empty()){Nalu* nal = _nalus.front();_nalus.pop();return nal;}else if (_status){return NULL;}else{ReadFromFile();Splite();if (!_nalus.empty()){Nalu* nal = _nalus.front();_nalus.pop();return nal;}}return NULL;
}void NaluFileReader::CloseFile()
{fclose(_file);_status = 0;
}void NaluFileReader::ReadFromFile()
{if (_status)return;if (_size != 0){// need seeklong offset = _size;fseek(_file, -offset, SEEK_CUR);_size = 0;}size_t size = fread(_buffer, 1, BUFF_SIZE, _file);if (size != BUFF_SIZE){_status = 1;}_size += size;
}int32_t NaluFileReader::FindStartCode(const uint8_t* buf, uint32_t size, uint8_t* prefix)
{uint32_t pos = 0;*prefix = 0;while (1){if (pos + 4 > size) return -1;if (buf[pos++] != 0x0)	continue;if (buf[pos++] != 0x0)	continue;if (buf[pos] == 0x01){*prefix = 3;break;}if (buf[pos++] != 0x0)	continue;if (buf[pos] == 0x01){*prefix = 4;break;}}return pos + 1;
}int NaluFileReader::Splite()
{uint32_t end_index = 0;uint8_t prefix = 0;uint8_t* buf_stream = _buffer;end_index = FindStartCode(buf_stream, _size, &prefix);if (prefix == 0){return -1;}while (1){uint8_t prefix_pre = prefix;end_index = FindStartCode(buf_stream + prefix, _size - prefix, &prefix);if (prefix == 0){if (_status == 1){Nalu* nalu = new Nalu(buf_stream, _size);_nalus.push(nalu);_size = 0;}break;}else{Nalu* nalu = new Nalu;nalu->Init(buf_stream, end_index - prefix + prefix_pre);_nalus.push(nalu);buf_stream += nalu->GetLenthEBSP();_size -= nalu->GetLenthEBSP();}}return 0;
}

3、使用读取器打印nalu信息

简单示例打印一下所有的nalu单元长度信息

#include <iostream>
#include "nalu_file_reader.h"
using namespace std;int main()
{NaluFileReader nal_reader;nal_reader.OpenFile("F:\\test\\source.h264");while (1){auto nal = nal_reader.GetNalu();if (!nal)break;nal->ParsePrefix();     // 解析前缀0x00000001nal->ParseRBSP();       // 去除防竞争字节nal->ParseHead();       // 解析nal头字段cout << "nal type:" << (int)nal->GetNalUnitType() << ",len:" << nal->GetLenthEBSP() << endl;delete nal;}
}