本文记录了H264视频码流解析，视频码流在视频播放器中的位置如下所示

原理

H.264原始码流是由一个一个的NALU组成的。其结构如下图所示。

其中每个NALU之间通过startcode（起始码）进行分隔，起始码分成两种：0x000001（3Byte）或者0x00000001（4Byte）。如果NALU对应的Slice为一帧的开始就用0x00000001，否则就用0x000001。

H.264码流解析的步骤就是首先从码流中搜索0x000001和0x00000001，分离出NALU；然后再分析NALU的各个字段。本程序可以从H.264码流中分析得到它的基本单元NALU，并且简单解析NALU首部的字段。

代码

#include <jni.h>
#include <string>
#include <math.h>

#ifdef ANDROID
#include <jni.h>
#include <android/log.h>
#define LOGE(format, ...)  __android_log_print(ANDROID_LOG_ERROR, "xohnffmpeg", format, ##__VA_ARGS__)
#define LOGI(format, ...)  __android_log_print(ANDROID_LOG_INFO,  "xohnffmpeg", format, ##__VA_ARGS__)
#else
#define LOGE(format, ...)  printf("xohnffmpeg" format "\n", ##__VA_ARGS__)
#define LOGI(format, ...)  printf("xohnffmpeg " format "\n", ##__VA_ARGS__)
#endif

typedef enum {
	NALU_TYPE_SLICE    = 1,
	NALU_TYPE_DPA      = 2,
	NALU_TYPE_DPB      = 3,
	NALU_TYPE_DPC      = 4,
	NALU_TYPE_IDR      = 5,
	NALU_TYPE_SEI      = 6,
	NALU_TYPE_SPS      = 7,
	NALU_TYPE_PPS      = 8,
	NALU_TYPE_AUD      = 9,
	NALU_TYPE_EOSEQ    = 10,
	NALU_TYPE_EOSTREAM = 11,
	NALU_TYPE_FILL     = 12,
} NaluType;
 
typedef enum {
	NALU_PRIORITY_DISPOSABLE = 0,
	NALU_PRIRITY_LOW         = 1,
	NALU_PRIORITY_HIGH       = 2,
	NALU_PRIORITY_HIGHEST    = 3
} NaluPriority;
 
 
typedef struct
{
	int startcodeprefix_len;      //! 4 for parameter sets and first slice in picture, 3 for everything else (suggested)
	unsigned len;                 //! Length of the NAL unit (Excluding the start code, which does not belong to the NALU)
	unsigned max_size;            //! Nal Unit Buffer size
	int forbidden_bit;            //! should be always FALSE
	int nal_reference_idc;        //! NALU_PRIORITY_xxxx
	int nal_unit_type;            //! NALU_TYPE_xxxx    
	char *buf;                    //! contains the first byte followed by the EBSP
} NALU_t;
 
FILE *h264bitstream = NULL;                //!< the bit stream file
 
int info2 = 0, info3 = 0;
 
static int FindStartCode2(unsigned char *Buf){
	if(Buf[0]!=0 || Buf[1]!=0 || Buf[2] !=1) return 0; //0x000001?
	else return 1;
}
 
static int FindStartCode3(unsigned char *Buf){
	if(Buf[0]!=0 || Buf[1]!=0 || Buf[2] !=0 || Buf[3] !=1) return 0;//0x00000001?
	else return 1;
}
 
 
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)
		LOGE ("GetAnnexbNALU: Could not allocate Buf memory\n");
 
	nalu->startcodeprefix_len = 3;
 
	if (3 != fread(Buf, 1, 3, h264bitstream)){
		free(Buf);
		return 0;
	}
	info2 = FindStartCode2(Buf);
	if(info2 != 1) {
		if(1 != fread(Buf+3, 1, 1, h264bitstream)){
			free(Buf);
			return 0;
		}
		info3 = FindStartCode3(Buf);
		if (info3 != 1){ 
			free(Buf);
			return -1;
		}else {
			pos = 4;
			nalu->startcodeprefix_len = 4;
		}
	}else{
		nalu->startcodeprefix_len = 3;
		pos = 3;
	}
	StartCodeFound = 0;
	info2 = 0;
	info3 = 0;
 
	while (!StartCodeFound){
		if (feof(h264bitstream)){
			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(h264bitstream);
		info3 = FindStartCode3(&Buf[pos-4]);
		if(info3 != 1)
			info2 = FindStartCode2(&Buf[pos-3]);
		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(h264bitstream, rewind, SEEK_CUR)){
		free(Buf);
		LOGE("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);//
	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);
}
 
/**
 * Analysis H.264 Bitstream
 * @param jstr_url    Location of input H.264 bitstream file.
 * H.264原始码流（又称为“裸流”）是由一个一个的NALU组成的
 * 每个NALU之间通过startcode（起始码）进行分隔，起始码分成两种：0x000001（3Byte）或者0x00000001（4Byte）。如果NALU对应的Slice为一帧的开始就用0x00000001，否则就用0x000001
 * H.264码流解析的步骤就是首先从码流中搜索0x000001和0x00000001，分离出NALU；然后再分析NALU的各个字段
 */
extern "C" JNIEXPORT jint JNICALL
Java_com_xohn_ffmpeg_AVUtils_h264Parser(
        JNIEnv *env,jobject /* this */,
        jstring jstr_url) {
	const char *url = env->GetStringUTFChars(jstr_url, NULL);
	h264bitstream = fopen(url, "rb+");
	env->ReleaseStringUTFChars(jstr_url,url);
	if (h264bitstream == NULL){
		return -1;
	}
	
	NALU_t *n;
	int buffersize = 100000;
 
	//FILE *myout=fopen("output_log.txt","wb+");
	//FILE *myout=stdout;
 
	n = (NALU_t*)calloc(1, sizeof (NALU_t));
	if (n == NULL){
		LOGE("Alloc NALU Error\n");
		return -1;
	}
 
	n->max_size = buffersize;
	n->buf = (char*)calloc(buffersize, sizeof (char));
	if (n->buf == NULL){
		free (n);
		LOGE ("AllocNALU: n->buf");
		return -1;
	}
 
	int data_offset = 0;
	int nal_num = 0;
	LOGI("-----+-------- NALU Table ------+---------+\n");
	LOGI(" NUM |    POS  |    IDC |  TYPE |   LEN   |\n");
	LOGI("-----+---------+--------+-------+---------+\n");
 
	while(!feof(h264bitstream)){
		int data_lenth;
		data_lenth = GetAnnexbNALU(n);
 
		char type_str[10] = {0};
		switch(n->nal_unit_type){
			case NALU_TYPE_SLICE:sprintf(type_str,"SLICE");break;
			case NALU_TYPE_DPA:sprintf(type_str,"DPA");break;
			case NALU_TYPE_DPB:sprintf(type_str,"DPB");break;
			case NALU_TYPE_DPC:sprintf(type_str,"DPC");break;
			case NALU_TYPE_IDR:sprintf(type_str,"IDR");break;
			case NALU_TYPE_SEI:sprintf(type_str,"SEI");break;
			case NALU_TYPE_SPS:sprintf(type_str,"SPS");break;
			case NALU_TYPE_PPS:sprintf(type_str,"PPS");break;
			case NALU_TYPE_AUD:sprintf(type_str,"AUD");break;
			case NALU_TYPE_EOSEQ:sprintf(type_str,"EOSEQ");break;
			case NALU_TYPE_EOSTREAM:sprintf(type_str,"EOSTREAM");break;
			case NALU_TYPE_FILL:sprintf(type_str,"FILL");break;
			default:sprintf(type_str,"UNKNOWN");break;
		}
		char idc_str[10] = {0};
		switch(n->nal_reference_idc>>5){
			case NALU_PRIORITY_DISPOSABLE:sprintf(idc_str,"DISPOS");break;
			case NALU_PRIRITY_LOW:sprintf(idc_str,"LOW");break;
			case NALU_PRIORITY_HIGH:sprintf(idc_str,"HIGH");break;
			case NALU_PRIORITY_HIGHEST:sprintf(idc_str,"HIGHEST");break;
			default:sprintf(idc_str,"UNKNOWN");break;
		}
 
		//fprintf(myout,"%5d| %8d| %7s| %6s| %8d|\n",nal_num,data_offset,idc_str,type_str,n->len);
		LOGI("%5d| %8d| %7s| %6s| %8d|\n",nal_num,data_offset,idc_str,type_str,n->len);
 
		data_offset = data_offset+data_lenth;
 
		nal_num++;
	}
 
	//free
	if (n){
		if (n->buf){
			free(n->buf);
			n->buf = NULL;
		}
		free (n);
	}
	return 0;
}

函数调用

AVUtils.getInstance().h264Parser(ROOT+"sintel.h264");

输出为该码流的NALU统计数据，如下图

参考文章：

雷神文章 https://blog.csdn.net/leixiaohua1020/article/details/50534369

项目git地址：

https://gitee.com/xohn/FFmpeg.git 中的FFMpeg1 - xohn_avutils_h264.cpp

Android 音视频入门03 H264视频码流解析

原理

代码

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