【AAC文件数据解析和ADTS frame】

参考雷神的博客，我使用的是VS2010，加载AAC文件，读取数据解析，如果没有AAC文件的，可以网上下载一个格式工厂，转换出一个AAC文件出来，注意文件尽量小一点

工程：

效果：

代码是使用雷神的代码，然后我加了一些注释，让刚入门的能降低理解难度：

// my1.cpp : 定义控制台应用程序的入口点。
//
 
#include "stdafx.h"
//C++中malloc、free的头文件
#include 
 
 
//解析ADTS frame结构
int getADTSframe(unsigned char* buffer, int buf_size, unsigned char* data ,int* data_size)
{
    int size = 0;
 
    if(!buffer || !data || !data_size )
	{
        return -1;
    }
 
    while(1)
	{
		//ADTS header占用的大小为7字节或者9字节，区别在于结尾是否有CRC效验
		//adts_fixed_header部分中的protection_absent为1时没有效验，为0时有效验，大小小于7字节就没有意义了
        if(buf_size  < 7 )
		{
            return -1;
        }
		//syncword占用12位，所以判断前12位，是否为0xFFF，用来分离AAC码流中每个ADTS frame
        if((buffer[0] == 0xff) && ((buffer[1] & 0xf0) == 0xf0) )
		{
			//frame_length是ADTS frame长度，按位存放，(第四个字节最后两位，第五个字节，第六个字节前3位)
            size |= ((buffer[3] & 0x03) <<11);     //high 2 bit
            size |= buffer[4]<<3;                //middle 8 bit
            size |= ((buffer[5] & 0xe0)>>5);        //low 3bit
            break;
        }
        --buf_size;
        ++buffer;
    }
 
    if(buf_size < size)
	{
        return 1;
    }
 
	//每次获取一个ADTS frame
    memcpy(data, buffer, size);
    *data_size = size;
 
    return 0;
}
 
int simplest_aac_parser(char *url)
{
    int data_size = 0;
    int size = 0;
    int cnt=0;
    int offset=0;
 
    FILE *myout=stdout;
 
    unsigned char *aacframe=(unsigned char *)malloc(1024*5);
    unsigned char *aacbuffer=(unsigned char *)malloc(1024*1024);
 
    FILE *ifile = fopen(url, "rb");
    if(!ifile)
	{
        printf("Open file error");
        return -1;
    }
 
    printf("-----+- ADTS Frame Table -+------+\n");
    printf(" NUM | Profile | Frequency| Size |\n");
    printf("-----+---------+----------+------+\n");
 
    while(!feof(ifile))
	{
		//返回读取对象个数，ifile中读取1024*1024-offset，到aacbuffer+offset
        data_size = fread(aacbuffer+offset, 1, 1024*1024-offset, ifile);
        unsigned char* input_data = aacbuffer;
 
        while(1)
        {
            int ret=getADTSframe(input_data, data_size, aacframe, &size);
            if(ret==-1)
			{
                break;
            }
			else if(ret==1)
			{
                memcpy(aacbuffer,input_data,data_size);
                offset=data_size;
                break;
            }
 
            char profile_str[10]={0};
            char frequence_str[10]={0};
 
			//使用的AAC级别，2位，0为AAC Main，1为 AAC LC (Low Complexity)，2为 AAC SSR (Scalable Sampling Rate)
            unsigned char profile=aacframe[2]&0xC0;
            profile=profile>>6;
            switch(profile)
			{
				case 0: sprintf(profile_str,"Main");break;
				case 1: sprintf(profile_str,"LC");break;
				case 2: sprintf(profile_str,"SSR");break;
				default:sprintf(profile_str,"unknown");break;
            }
 
			//采样率sampling_frequency_index，Sampling Frequencies[ ]数组查询对于采样率
            unsigned char sampling_frequency_index=aacframe[2]&0x3C;
            sampling_frequency_index=sampling_frequency_index>>2;
 
            switch(sampling_frequency_index)
			{
				case 0: sprintf(frequence_str,"96000Hz");break;
				case 1: sprintf(frequence_str,"88200Hz");break;
				case 2: sprintf(frequence_str,"64000Hz");break;
				case 3: sprintf(frequence_str,"48000Hz");break;
				case 4: sprintf(frequence_str,"44100Hz");break;
				case 5: sprintf(frequence_str,"32000Hz");break;
				case 6: sprintf(frequence_str,"24000Hz");break;
				case 7: sprintf(frequence_str,"22050Hz");break;
				case 8: sprintf(frequence_str,"16000Hz");break;
				case 9: sprintf(frequence_str,"12000Hz");break;
				case 10: sprintf(frequence_str,"11025Hz");break;
				case 11: sprintf(frequence_str,"8000Hz");break;
				default:sprintf(frequence_str,"unknown");break;
            }
 
 
            fprintf(myout,"%5d| %8s|  %8s| %5d|\n",cnt,profile_str ,frequence_str,size);
            data_size -= size;
            input_data += size;
            cnt++;
        }
 
    }
    fclose(ifile);
    free(aacbuffer);
    free(aacframe);
 
    return 0;
}
 
int _tmain(int argc, _TCHAR* argv[])
{
	simplest_aac_parser("F:/123.aac");//acc文件路径
 
	return 0;
}

注意：

1、自己准备一个AAC的文件放在自己觉得方便的路径

2、使用调试模式打断点查看结果，在_tmain函数的return 0，打上断点，不要一下跑完了，

ADTS frame结构和信息：