MP4音頻解碼信息

文章轉載自：http://blog.csdn.net/flyingqr/archive/2010/02/02/5282600.aspx 版權歸原作者，編輯：小乙哥

MP4文件格式分為頭部和數據兩部分，頭部是由許多被稱作Atom的結構單元嵌套或排列而成，數據部分則完全為實際數據不包含元信息，因此具體解碼時音視頻幀的位置和大小都要在頭部獲取。詳細內容見以下鏈接：
http://wqyuwss.52rd.net
這里總結下音頻解碼信息獲取的一些經驗，當然詳細內容需要查看quick time file format的文檔。
MP4的音頻解碼信息保存在如下嵌套的Atom中，{moov{mdia{minf{smhd{stbl{stsd}}}}}}
stsd可能包括多個音頻信息的描述，結構如下：

typedef struct stsdtable
{
????unsigned int size;//Atom大小
????char format[4];//音頻編碼格式
????int res1;
????int ref;
????short version;//版本
????short pad1;
????int pad2;
????short channels;//聲道
????short bitspersample;
????short compress_id;
????short res2;
????short samplerate1;//采樣率
????short samplerate2;
????//{if(version==1)

????????int sampleperpacket;
????????int bytesperpacket;
????????int bytesperframe;
????????int bytespersample;
????//}

} stsdtable;

其中format對應音頻編碼格式：
PCM_S32BE,? in32
PCM_S32LE,? in32
PCM_S24BE,? in24
PCM_S24LE,? in24
PCM_S16BE,? twos // 16 bits //
PCM_S16LE,? sowt //?
PCM_S16LE,? lpcm
PCM_F32BE,? fl32
PCM_F64BE,? fl64
PCM_S8,???? sowt
PCM_U8,???? raw? // 8 bits unsigned
PCM_U8,???? NONE // uncompressed
PCM_MULAW,? ulaw //
PCM_ALAW,?? alaw //
ADPCM_IMA_QT, ima4 // IMA-4 ADPCM //
MACE3,????? MAC3 // Macintosh Audio Compression and Expansion 3:1 ///
MACE6,????? MAC6 // Macintosh Audio Compression and Expansion 6:1 //
MP3,??????? .mp3 // MPEG layer 3 */
uint8_t moov[] = "moov";
uint8_t trak[] = "trak";
uint8_t mdia[] = "mdia";
uint8_t minf[] = "minf";
uint8_t stbl[] = "stbl";
uint8_t stsd[] = "stsd";
uint8_t stsc[] = "stsc";
uint8_t stsz[] = "stsz";
uint8_t stco[] = "stco";
uint8_t ftyp[] = "ftyp";
uint8_t mdat[] = "mdat";

typedef struct Atom
{
????unsigned int size;
????uint8_t tag[4];
????int ver_flag;
????unsigned int num_of_entries;
????unsigned int pos;
????uint8_t *data;
} Atom;



uint8_t kmp3[] = {0x6D,0x73,0x00,0x55};
uint8_t fmp3[] = ".mp3";
uint8_t raw[] = "raw ";

uint8_t wave[] = "wave";
uint8_t mp4a[] = "mp4a";
uint8_t enca[] = "enca";//encrypted to ISO/IEC 14496-12 or 3GPP standards

uint8_t smar[] = "smar";//encoded to 3GPP GSM 6.10 AMR narrowband standards

uint8_t sawb[] = "sawb";//encoded to 3GPP GSM 6.10 AMR wideband standards

uint8_t m4ds[] = "m4ds";//encoded to ISO/IEC 14496-10 AVC standards

uint8_t esds[] = "esds";
uint8_t fram[] = "fram";


#define MKTAG(a,b,c,d) (a | (b << 8) | (c << 16) | (d << 24))
typedef struct AVCodecTag {
????int id;
????unsigned int tag;
} AVCodecTag;


typedef struct stsdtable
{
????unsigned int size;
????char format[4];
????int res1;
????int ref;
????short version;
????short pad1;
????int pad2;
????short channels;
????short bitspersample;
????short compress_id;
????short res2;
????short samplerate1;
????short samplerate2;
????//{if(version==1)

????????int sampleperpacket;
????????int bytesperpacket;
????????int bytesperframe;
????????int bytespersample;
????//}

} stsdtable;


typedef struct sampletable
{
????unsigned int size;
????unsigned int id_of_sd;
} sampletable;
//MP4Analyze.cpp
#include "MP4Analyze.h"
#include <vector>
#include <map>
#include <iostream>
#include <string>
#ifdef WIN32
#include <winsock2.h>
#pragma comment(lib, "Ws2_32.lib")
#pragma warning (disable:4786)
#endif

#ifdef __GNUG__
#include <netinet/in.h>
#endif
using namespace std;




int check_format(uint8_t *data, int size)
{
????if(strncmp((char*)moov,(char*)(data+4),4)==0 ||
????????strncmp((char*)ftyp,(char*)(data+4),4)==0 ||strncmp((char*)mdat,(char*)(data+4),4)==0 )
????????return 0;
????return -1;
}

unsigned int get_size(const uint8_t *data,int size)
{
????unsigned int tmp = 0;
????for(int i=0; i<size; ++i)
????{
????????tmp <<= 8;
????????tmp += *data++;
????}
????return tmp;
}

int seek_tag(uint8_t tag[],uint8_t *data, unsigned int size1,uint8_t **pos,unsigned int *size2)
{
????if(data == NULL || size1 == 0)
????????return -1;
????unsigned int tag_size = get_size(data,4);
????if(tag_size >size1 + 8)
????????return -1;
????unsigned int tmp = 0;
????while(strncmp((char*)data+4,(char*)tag,4) != 0)
????{
????//????printf("%s/n",data+4);

????????if(tag_size==0)
????????????return -1;
????????if(tag_size < size1 + 8)
????????{
????????????data += tag_size;
????????????tmp += tag_size;
????????}
????????else
????????????return -1;
????????tag_size = get_size(data,4);
????}
????printf("find :%c%c%c%c/n",tag[0],tag[1],tag[2],tag[3]);
????if(tmp + tag_size > size1 )
???? printf("warning: the atom may be not complete!/n");
????*pos = data+8;
????*size2 = tag_size -8;
????return tmp;
}

v文章轉載自：http://blog.csdn.net/flyingqr/archive/2010/02/02/5282600.aspx 版權歸原作者，編輯：小乙哥

vector<stsdtable>& get_audio_info(uint8_t *data, unsigned int size, vector<stsdtable>& stable)//stsd

{
????uint8_t * datapos = data;
????Atom *stsd_audio =(Atom *)data;
????int tmp_size = 16;

????printf("size : %u/n",ntohl(stsd_audio->size));
????printf("num_entr: %u/n",ntohl(stsd_audio->num_of_entries));

????for(int i=0; i < ntohl(stsd_audio->num_of_entries); ++i)
????{
????????if(tmp_size > size)//注意

????????????return stable;
????????datapos += tmp_size;
????????stsdtable * audio_entry = (stsdtable *)(datapos);
????????stable.push_back(*audio_entry);//這里存入的是網絡序的數據，使用時需進行轉換

????????tmp_size += ntohl(audio_entry->size);

????
????????printf("--tablesize: %d/n",ntohl(audio_entry->size));
????????printf("--format : %s/n",audio_entry->format);
????????printf("--version : %d/n",ntohs(audio_entry->version));
????????printf("--channels: %d/n",ntohs(audio_entry->channels));
????????printf("--bitpersam: %d/n",ntohs(audio_entry->bitspersample));
????????printf("--IDcompress: %d/n",ntohs(audio_entry->compress_id));????
????????printf("--samplerate: %d.%d/n",ntohs(audio_entry->samplerate1),ntohs(audio_entry->samplerate2));
????????

???? tmp_size = sizeof(stsdtable);
????????if(ntohs(audio_entry->version)==0)
????????{
????????????tmp_size -= 16;
????????}
????????datapos += tmp_size;
????????//if(ntohs(audio_entry->compress_id)==-2)//此處尚需考證

????????if(ntohl(audio_entry->size) > sizeof(stsdtable))
????????{
????????????printf("----atom size:%d/n",get_size(datapos,4));
????????????printf("----atom name:%c%c%c%c/n",datapos[4],datapos[5],datapos[6],datapos[7]);
????????????if(strncmp((char*)datapos,(char*)esds,4)==0)
????????????{
????????????????//handle esds

????????????}
????????}
????}
????return stable;
}

map<unsigned int,sampletable> & get_packet_offset(uint8_t *STBL[], map<unsigned int,sampletable>& table)
{
????//table.insert(pair<long,sampletable>(1,sample));

????unsigned int num_sam_to_chunk = get_size(STBL[0]-4,4);//stsc

????unsigned int num_sample = get_size(STBL[1]-4,4);//stsz

????unsigned int num_chunk = get_size(STBL[2]-4,4);//stco

????unsigned int chunk_index = 0;
????unsigned int next_chunk_index = 0;
????uint8_t *cur_sam_to_chunk = STBL[0];
????uint8_t *cur_sam_size = STBL[1];
????uint8_t *cur_chunk_offset = STBL[2];
????sampletable sample;
????printf("number of stsc entries:%d /nnumber of sample size:%d /nnumber of chunk offset:%d/n",num_sam_to_chunk,num_sample,num_chunk);
????for(unsigned int i = 0; i < num_sam_to_chunk; ++i)//對所有的entries

????{
????????chunk_index = get_size(cur_sam_to_chunk,4);
????????next_chunk_index = get_size(cur_sam_to_chunk+12,4);
????????sample.id_of_sd = get_size(cur_sam_to_chunk+8,4);
????????if(i == num_sam_to_chunk -1)//最后一個

????????{
????????????next_chunk_index = num_chunk+1;
????????}
????????printf("chunk_index:(%d---%d)/n",chunk_index,next_chunk_index);
????????for(unsigned int k=chunk_index; k < next_chunk_index; ++k)//當前chunk序號到下一個chunk序號之間的chunk

????????{//處理所有重復的chunk

????????????printf("chunk_index:%d sample num:%d/n",chunk_index,get_size(cur_sam_to_chunk+4,4));
????????????unsigned int offset = get_size(cur_chunk_offset+(chunk_index-1)*4,4);
????????????for(unsigned int j=0; j < get_size(cur_sam_to_chunk+4,4); ++j)//chunk內地sample數目

????????????{//處理該chunk中的sample

????????????????sample.size = get_size(cur_sam_size,4);????
????????????????printf("--sample offset:%d %x size:%d/n",offset,offset,sample.size);
????????????????table.insert(pair<unsigned int,sampletable>(offset,sample));
????????????????offset = offset + sample.size;
????????????????cur_sam_size += 4;
????????????}
????????????system("pause");
????????????chunk_index++;
????????}
????????cur_sam_to_chunk += 12;
????}
????return table;
}
文章轉載自：http://blog.csdn.net/flyingqr/archive/2010/02/02/5282600.aspx 版權歸原作者，編輯：小乙哥

int seek_audio_atom( uint8_t *data1, unsigned int size1)
{
????uint8_t tag[] = "mdiaminfsmhd";
????uint8_t *datapos;
????unsigned int tag_size;
????uint8_t *data;
????unsigned int size;
????int offset_of_atom = 0;
????if((offset_of_atom = seek_tag(moov, data1, size1, &data, &size)) == -1)
????????return -1;
????if(offset_of_atom + size >size1)
????{ //some handles

????????printf("moov atom is not complete,need more data");
????}
????data1 = data;
????size1 = size;
????uint8_t *nexttrak = data;
????unsigned int traksize = size;
????int i=0;
????while(1)
????{
????????printf("-----/n");
????????if(seek_tag(trak, nexttrak, traksize, &datapos, &tag_size) != -1)
????????{
????????????nexttrak = datapos + tag_size;
????????????if(size1 < (nexttrak - data1))
????????????????return -1;
????????????traksize = size1 - (nexttrak - data1);
????????????data = datapos;
????????????size = tag_size;
????????}
????????else
????????{
????????????return -1;
????????}
????????i=0;
????????while(i<3)
????????{
????????????if(seek_tag(tag+i*4, data, size, &datapos, &tag_size) != -1)
????????????{
????????????????if(i==2)
???????????????? break;
????????????????data = datapos;
????????????????size = tag_size;
????????????????++i;
????????????}
????????????else
????????????{
????????????????break;
????????????}
????????}
????????if(strncmp("smhd",(char*)(datapos-4),4) == 0)
????????{
????????????if(seek_tag(stbl, data, size, &datapos, &tag_size)!= -1)
????????????{
????????????????printf("—find audio stbl—!/n");
????????????????data = datapos;
????????????????size = tag_size;

????????????????if(seek_tag(stsd, data, size, &datapos, &tag_size) != -1)
????????????????{
????????????????????vector<stsdtable> stable; //音頻信息

????????????????????get_audio_info(datapos-8, tag_size,stable);
????????????????}

????????????????uint8_t *STBL[3] ={NULL,NULL,NULL};//

????????????????uint8_t *datapos1;
????????????????unsigned int tag_size1;//

????????????????if(seek_tag(stsc, data, size, &datapos1, &tag_size1) != -1)
????????????????{
????????????????????STBL[0] = datapos1 + 8;
????????????????}
????????????????uint8_t *datapos2;
????????????????unsigned int tag_size2;
????????????????if(seek_tag(stsz, data, size, &datapos2, &tag_size2) != -1)
????????????????{
????????????????????STBL[1] = datapos2 + 12;
????????????????}
????????????????uint8_t *datapos3;
????????????????unsigned int tag_size3;
????????????????if(seek_tag(stco, data, size, &datapos3, &tag_size3) != -1)
????????????????{
????????????????????STBL[2] = datapos3 + 8;
????????????????}
????????????????if(STBL[0] && STBL[1] && STBL[2] )
????????????????{
????????????????????map<unsigned int,sampletable> postable;//音頻幀信息

????????????????????get_packet_offset(STBL,postable);
????????????????}
????????????}
????????????return 0;
????????}
????}
????return -1;
}
int main(char arg, char *argv[])
{
????FILE *mp4;
????cout<<"please input the file name :"<<endl;
????string filename;
????cin>>filename;
????mp4 = fopen(filename.c_str(),"rb");
????uint8_t buffer[300000];
????fread(buffer,1,300000,mp4);

????seek_audio_atom((uint8_t*)buffer,300000);

????fclose(mp4);
????return 0;
}

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