H264 raw stream获取nalu的长度信息

代码是从上一篇博客[1]中摘取出来的，只提取nalu的在内存中的偏移量和长度（均刨除起始码的长度）。
h264_parser.h

#pragma once
#include <stdio.h>
#include <stdint.h>
namespace media{
struct H264NALU{
const uint8_t *data;
size_t size;
size_t start_code_size;
};
class H264Parser{
public:enum Result {kOk,kInvalidStream,      // error in streamkUnsupportedStream,  // stream not supported by the parserkEOStream,           // end of stream};
void SetStream(const uint8_t* stream, size_t stream_size);
H264Parser::Result AdvanceToNextNALU(H264NALU* nalu);
bool LocateNALU(size_t* nalu_size, size_t* start_code_size);
static bool FindStartCode(const uint8_t* data,size_t data_size,size_t* offset,size_t* start_code_size);
private:const uint8_t *stream_{nullptr};size_t bytes_left_;
};
}

h264_parser.cc

#include <memory.h>
#include "h264_parser.h"
#include "logging.h"
#define NOTREACHED() CHECK(false)
#define DVLOG(x) VLOG(x)
namespace media{
static inline bool IsStartCode(const uint8_t* data) {return data[0] == 0x00 && data[1] == 0x00 && data[2] == 0x01;
}
void H264Parser::SetStream(const uint8_t* stream, size_t stream_size){stream_=stream;bytes_left_=stream_size;
}
H264Parser::Result H264Parser::AdvanceToNextNALU(H264NALU* nalu){size_t start_code_size;size_t nalu_size_with_start_code;if (!LocateNALU(&nalu_size_with_start_code, &start_code_size)) {DVLOG(4) << "Could not find next NALU, bytes left in stream: "<< bytes_left_;stream_ = nullptr;bytes_left_ = 0;return kEOStream;}nalu->data = stream_ + start_code_size;nalu->size = nalu_size_with_start_code - start_code_size;nalu->start_code_size=start_code_size;DVLOG(4) << "NALU found: size=" << nalu_size_with_start_code;// Move parser state to after this NALU, so next time AdvanceToNextNALU// is called, we will effectively be skipping it;// other parsing functions will use the position saved// in bit reader for parsing, so we don't have to remember it here.stream_ += nalu_size_with_start_code;bytes_left_ -= nalu_size_with_start_code;return kOk;
}
bool H264Parser::LocateNALU(size_t* nalu_size, size_t* start_code_size){// Find the start code of next NALU.size_t nalu_start_off = 0;size_t annexb_start_code_size = 0;if (!FindStartCode(stream_, bytes_left_,&nalu_start_off, &annexb_start_code_size)) {DVLOG(4) << "Could not find start code, end of stream?";return false;}// Move the stream to the beginning of the NALU (pointing at the start code).stream_ += nalu_start_off;bytes_left_ -= nalu_start_off;const uint8_t* nalu_data = stream_ + annexb_start_code_size;off_t max_nalu_data_size = bytes_left_ - annexb_start_code_size;if (max_nalu_data_size <= 0) {DVLOG(3) << "End of stream";return false;}// Find the start code of next NALU;// if successful, |nalu_size_without_start_code| is the number of bytes from// after previous start code to before this one;// if next start code is not found, it is still a valid NALU since there// are some bytes left after the first start code: all the remaining bytes// belong to the current NALU.size_t next_start_code_size = 0;size_t nalu_size_without_start_code = 0;if (!FindStartCode(nalu_data, max_nalu_data_size,&nalu_size_without_start_code, &next_start_code_size)) {nalu_size_without_start_code = max_nalu_data_size;}*nalu_size = nalu_size_without_start_code + annexb_start_code_size;*start_code_size = annexb_start_code_size;return true;
}
bool H264Parser::FindStartCode(const uint8_t* data,size_t data_size,size_t* offset,size_t* start_code_size){size_t bytes_left = data_size;while (bytes_left >= 3) {// The start code is "\0\0\1", ones are more unusual than zeroes, so let's// search for it first.const uint8_t* tmp =reinterpret_cast<const uint8_t*>(memchr(data + 2, 1, bytes_left - 2));if (!tmp) {data += bytes_left - 2;bytes_left = 2;break;}tmp -= 2;bytes_left -= tmp - data;data = tmp;if (IsStartCode(data)) {// Found three-byte start code, set pointer at its beginning.*offset = data_size - bytes_left;*start_code_size = 3;// If there is a zero byte before this start code,// then it's actually a four-byte start code, so backtrack one byte.if (*offset > 0 && *(data - 1) == 0x00) {--(*offset);++(*start_code_size);}return true;}++data;--bytes_left;}// End of data: offset is pointing to the first byte that was not considered// as a possible start of a start code.// Note: there is no security issue when receiving a negative |data_size|// since in this case, |bytes_left| is equal to |data_size| and thus// |*offset| is equal to 0 (valid offset).*offset = data_size - bytes_left;*start_code_size = 0;return false;
}
}

test_main.cc

#include <iostream>
#include "h264_parser.h"
using namespace std;
using namespace media;
int main()
{char fake_h264[]={0x00,0x00,0x00,0x01,0x12,0x12,0x12,0x00,0x00,0x01,0x12,0x12,0x12,0x12,0x12,0x12,0x12,0x12,0x12};uint8_t *data=(uint8_t*)fake_h264;int data_size=sizeof(fake_h264);H264Parser parser;parser.SetStream(data,data_size);H264NALU nalu;while(true){if(parser.AdvanceToNextNALU(&nalu)==H264Parser::kOk){std::cout<<"size "<<nalu.size<<" start code len "<<nalu.start_code_size<<std::endl;}else{break;}}return 0;
}

里面有一些调试信息，需要log模块，可以去这里下载[2]。不想下载就注释掉了那些DVLOG这类代码。
Reference:
[1]h264 raw stream parser-读取H264裸流信息
[2]log

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