MP3文件头部信息解码- ID3V1

ID3V1

mp3解码的课题断断续续做了一年多了，这是我学习c语言之后想自己写的第一个课题，如果时光倒退，冒出这个想法的第一时间，我会给自己一个嘴巴子，搞搞贪吃蛇、五子棋什么的不好，非要搞mp3解码，为了这个，这一年我都忘记自己看了多少论文了。

各种论坛上有巨量的关于这个课题的文章，其中大量的都是头部信息的，盖上个文件解码的标题，白白浪费了宝宝很多时间。凭借着一股傻乎劲，宝宝从一无所知，逐渐也揭开了mp3的面纱，但是有些细节还是没摸透。并且，宝宝成功的卡在了哈夫曼码区。

宝宝心里苦呀，凭我的智商又不能完全搞得了整个MP3的解码，不搞完它，心理又始终惦记着，不从这个坑里走出来，宝宝人大概就废了，于是宝宝含着眼泪继续再一次卷土重来，这一次一定要把这个课题给结了。

文件结构

MP3文件的结构是这个样子的：

这是mp3文件宏观的样子，最主要的是音频数据，但宝宝现在还动不了它，所以关于它的各种例如心理学模型，哈夫曼编解码，傅里叶变换之类的，统统先不搞，下一个阶段再收拾它。

宝宝现在就盯准头部和尾部，就是传说的ID3V1和V2。
传统的mp3要么是 头部+音频数据 要么是 音频数据+尾部
但是自从ID3V2.4之后，就变成可以这个样子：头部 + 音频数据 + 尾部

ID3

这货大约是一种在mp3文件中附加例如歌手等信息的一种标准，它不是mp3的必要部分，mp3解码也用不上它，实际上mp3文件可以仅仅只有 音频数据
ID3v1可以在音频数据后面附加128字节的信息，为了在文件中附加更多的信息，于是有了ID3V2，它的升级版，为了不破坏ID3V1的读写，它放到了头部，并且采用了变长的方式。以下是它的版本

从其他大佬的文章中可以看到ID3V2有四个版本，但是从我保存的mp3文件中，并没有找到2.1和2.2的，暂时也没有找到跟这两个版本相关的资料。
官方传送门
ID3V2.3
ID3V2.4

ID3V1

ID3V1的结构非常简单，只有128字节

另：有资料说保留位和音轨号的两个byte属于附注，咱也不懂，咱也不敢问。
ps：看到有资料说，id3v1 有两个版本，一个是v1，一个是v1.1，1.1版本就是从附注中划出了音轨部分的两个字节

数据结构：

typedef struct id3v1
{
char	Tag[3];
char	Title[30];
char	Artist[30];
char	Album[30];
char	Year[4];
char	Comment[28];
unsigned char	Reserved;
unsigned char	TrackNum;
unsigned char	GenreIndex;
}ID3V1;

ID3V1略烦人的地方就是GenreIndex，它定义了140多种音乐类型，据说原来有差不多100种，然后Winamp扩充到125种，算上其他的，总共有140多种，要想知道这个值里的对应啥类型，还得建个表

#define GENRE_INDEX_MAX
148
char *Genre[GENRE_INDEX_MAX]=
{
"Blues","ClassicRock","Country","Dance","Disco","Funk","Grunge","Hip-Hop",
"Jazz","Metal","NewAge","Oldies","Other","Pop","R&B","Rap",
"Reggae","Rock","Techno","Industrial","Alternative","Ska","Deathl","Pranks",
"Soundtrack","Euro-Techno","Ambient","Trip-Hop","Vocal","Jazz+Funk","Fusion","Trance",
"Classical","Instrumental","Acid","House","Game","SoundClip","Gospel","Noise",
"AlternRock","Bass","Soul","Punk","Space","Meditative","InstrumentalPop","InstrumentalRock",
"Ethnic","Gothic","Darkwave","Techno-Industrial","Electronic","Pop-Folk","Eurodance","Dream",
"SouthernRock","Comedy","Cult","Gangsta","Top40","ChristianRap","Pop/Funk","Jungle",
"NativeAmerican","Cabaret","NewWave","Psychadelic","Rave","Showtunes","Trailer","Lo-Fi",
"Tribal","AcidPunk","AcidJazz","Polka","Retro","Musical","Rock&Roll","HardRock",
//Winamp扩充
"Folk","Folk-Rock","NationalFolk","Swing","FastFusion","Bebob","Latin","Revival",
"Celtic","Bluegrass","Avantgarde","GothicRock","ProgessiveRock","PsychedelicRock","SymphonicRock","SlowRock",
"BigBand","Chorus","EasyListening","Acoustic","Humour","Speech","Chanson","Opera",
"ChamberMusic","Sonata","Symphony","BootyBass","Primus","PornGroove","Satire","SlowJam",
"Club","Tango","Samba","Folklore","Ballad","PowerBallad","RhythmicSoul","Freestyle",
"Duet","PunkRock","DrumSolo","Acapella","Euro-House","DanceHall",
//其他扩充
"Goa","Drum&Bass","Club-House","Hardcore","Terror","Indie","BritPop","Negerpunk",
"PolskPunk","Beat","ChristianGangstaRap","Heavyl","Blackl","Crossover","ContemporaryChristian","ChristianRock",
"Merengue","Salsa","Trashl","Anime","JPop","Synthpop"
};

完整的测试

#include <stdio.h>
#define GENRE_INDEX_MAX
148
typedef struct id3v1
{
char	Tag[3];
char	Title[30];
char	Artist[30];
char	Album[30];
char	Year[4];
char	Comment[28];
unsigned char	Reserved;
unsigned char	TrackNum;
unsigned char	GenreIndex;
}ID3V1;
char *Genre[GENRE_INDEX_MAX]=
{
"Blues","ClassicRock","Country","Dance","Disco","Funk","Grunge","Hip-Hop",
"Jazz","Metal","NewAge","Oldies","Other","Pop","R&B","Rap",
"Reggae","Rock","Techno","Industrial","Alternative","Ska","Deathl","Pranks",
"Soundtrack","Euro-Techno","Ambient","Trip-Hop","Vocal","Jazz+Funk","Fusion","Trance",
"Classical","Instrumental","Acid","House","Game","SoundClip","Gospel","Noise",
"AlternRock","Bass","Soul","Punk","Space","Meditative","InstrumentalPop","InstrumentalRock",
"Ethnic","Gothic","Darkwave","Techno-Industrial","Electronic","Pop-Folk","Eurodance","Dream",
"SouthernRock","Comedy","Cult","Gangsta","Top40","ChristianRap","Pop/Funk","Jungle",
"NativeAmerican","Cabaret","NewWave","Psychadelic","Rave","Showtunes","Trailer","Lo-Fi",
"Tribal","AcidPunk","AcidJazz","Polka","Retro","Musical","Rock&Roll","HardRock",
//Winamp扩充
"Folk","Folk-Rock","NationalFolk","Swing","FastFusion","Bebob","Latin","Revival",
"Celtic","Bluegrass","Avantgarde","GothicRock","ProgessiveRock","PsychedelicRock","SymphonicRock","SlowRock",
"BigBand","Chorus","EasyListening","Acoustic","Humour","Speech","Chanson","Opera",
"ChamberMusic","Sonata","Symphony","BootyBass","Primus","PornGroove","Satire","SlowJam",
"Club","Tango","Samba","Folklore","Ballad","PowerBallad","RhythmicSoul","Freestyle",
"Duet","PunkRock","DrumSolo","Acapella","Euro-House","DanceHall",
//其他扩充
"Goa","Drum&Bass","Club-House","Hardcore","Terror","Indie","BritPop","Negerpunk",
"PolskPunk","Beat","ChristianGangstaRap","Heavyl","Blackl","Crossover","ContemporaryChristian","ChristianRock",
"Merengue","Salsa","Trashl","Anime","JPop","Synthpop"
};
int main()
{
ID3V1 id3;
FILE *fp;
fp = fopen("ID3V1.mp3","rb");
if(fp == NULL)return -1;
fseek(fp,-128,SEEK_END);
fread((void*)&id3,1,128,fp);
printf("----------------ID3V1Info----------------n");
if(strcmp(id3.Tag,"TAG") != 0)
{
printf("not exist ID3V1");
return -1;
}
else
{
printf("Tag:tt%.3sn",id3.Tag);
printf("Title:tt%.30sn",id3.Title);
printf("Artist:tt%.30sn",id3.Artist);
printf("Album:tt%.30sn",id3.Album);
printf("Year:tt%.4sn",id3.Year);
printf("Comment:t%.28sn",id3.Comment);
printf("Reserved:t%xn",id3.Reserved);
printf("TrackNum:t%xn",id3.TrackNum);
printf("Genre:tt%sn",id3.GenreIndex < GENRE_INDEX_MAX ? Genre[id3.GenreIndex]:"null");
}
printf("----------------------------------------nn");
fclose(fp);
return 0;
}

关于ID3更多的信息

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