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Чтение файла в формате mp3

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Чтение файла в формате mp3


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Формат очень простой. Для начала приведу таблицу с описанием заголовка (он идет сразу с сначала файла):

Name of Field

Bit Numbers

Code to Extract

Meaning

Frame Sync

A frame can, in principle, start at an arbitray byte offset into the audio stream. The beginning of a frame header is indicated by 11 ones, starting at the beginning of a byte.

inBuf[ 0 ] 0:7

InBuf[ 0 ]

Since the first 11 bits of a header are all 1s, inBuf[ 0 ] must have a decimal value of 255, which is eight ones in binary.

Frame Sync continued

inBuf[ 1 ] 5:7

(InBuf[ 1 ] >> 5) & 7

If inBuf[ 0 ] is 255, and if the first three bits of the next byte have the value 7 (three 1s in binary), the beginning of a valid MP3 header has been found.

Audio Version (phase)

inBuf[ 1 ] 3:4

(inBuf[ 1 ] >>3) & 3

The next two bits tell the MPEG version:

0 = MPEG-2.5 (a non-standard extension to MPEG-2)1 = reserved2 = MPEG-23 = MPEG-1

Layer

inBuf[ 1 ] 1:2

(inBuf[ 1 ] >> 1) & 3

The next two bits tell the layer:

0 = reserved1 = Layer III2 = Layer II3 = Layer I

Protection Bit

inBuf[ 1 ] 0

InBuf[ 1 ] & 1

If this bit is 0, the header is followed by two bytes of error detection bits before the audio data starts.

Bit Rate Index

inBuf[ 2 ] 4:7

(InBuf[ 2 ] >> 4) & 15

The next four bits are a row index into a doubly subscripted arry of bit rates.

See note below.

Sampling Rate Index

inBuf[ 2 ] 2:3

(inBuf[ 2 ] >>) & 3

For MPEG-1, the values are as follows:

0 = 44,100 Hz1 = 48,000 Hz2 = 32,000 Hz3 = reserved

Padding Bit

InBuf[ 2 ] 1

(inBuf[ 2 ] >> 1) & 1

If this bit is a 1 and the layer is III, the frame has an extra (unused) byte at the end. For layers I and II the padding amount, if present, is four bytes.

Private Bit

inBuf[ 2 ] 0

InBuf[ 2 ] & 1

Different programs can interpret this bit different ways.

Channel Mode

inBuf[ 3 ] 6:7

(inBuf[ 3 ] >> 6) & 3

This two bit code tells whether the information is in stereo or not:

0 = Stereo1 = Joint Stereo2 = Dual Channel3 = Single Channel

Mode Extension

(Only if Joint Stereo)

inBuf[ 3 ] 4:5

(inBuf[ 3 ] >> 4) & 3

Used internally by the decoding algorithm.

Copyright

inBuf[ 3 ] 3

(inBuf[ 3 ] >> 3) & 1

If this bit is set, the audio material is copyrighted.

Original

inBuf[ 3 ] 2

(inBuf[ 3 ] >> 2) & 1

If this bit is set, this file is the orginal media used to hold the audio information.

Emphasis

inBuf[ 3 ] 0:1

InBuf[ 3 ] & 3

Used internally by the decoding algorithm.


Notes on the Bit Rate Table:

The column index for the Bit Rate table is derived from the combination of the phase and layer as follows:

0 Phase 1, Layer I

1 Phase 1, Later II

2 Phase 1, Layer III

3 Phase 2 or 2.5, Layer I

4 Phase 2 or 2.5, Layer II or III

The row index should never equal fifteen.

The Bit Rate Table is avalable as a public array of int named bitRateTable in class MP3header.


Информация о исполнителе, альбоме, годе, жанре храниться в последних 128 байтах файла. Следующая таблица описывает формат к котором она храниться:

Bytes

Meaning

0:2

Must be "TAG".
If not, there is no ID3 tag in this file

3:32

Song Title

33:62

Performer's Name

63:92

Name of the Album

93:96

Year

97:126

Comment

127

Genre

Пример класса, вычитывающий информацию из ID3V1 TAGS:

import java.io.*; public class MP3header { private String Artist=""; private String Album=""; private String Song=""; private String fname=""; private long bitrate=0; private long year=0; private long stereo=0; private long fsize=0; static private int[][] bitRateTable = { // Ph 1L-I Ph1 L-II Ph1 L-III Ph2 L-I Ph2 L-II&III { 0, 0, 0, 0, 0 }, { 32000, 32000, 32000, 32000, 8000 }, { 64000, 48000, 40000, 48000, 16000 }, { 96000, 56000, 48000, 56000, 24000 }, { 128000, 64000, 56000, 64000, 32000 }, { 160000, 80000, 64000, 80000, 40000 }, { 192000, 96000, 80000, 96000, 48000 }, { 224000, 112000, 96000, 112000, 56000 }, { 256000, 128000, 112000, 128000, 64000 }, { 288000, 160000, 128000, 144000, 80000 }, { 320000, 192000, 160000, 160000, 96000 }, { 352000, 224000, 192000, 176000, 112000 }, { 384000, 256000, 224000, 192000, 128000 }, { 416000, 320000, 256000, 224000, 144000 }, { 448000, 384000, 320000, 256000, 160000 }, { -1, -1, -1, -1, -1 }, }; public void setArtist(String s) { Artist=s.trim(); } public String getArtist() { return(Artist.trim()); } public void setAlbum(String s) { Album=s.trim(); } public String getAlbum() { return(Album.trim()); } public void setSong(String s) { Song=s.trim(); } public String getSong() { return(Song.trim()); } public String getFName() { return(fname.trim()); } public long getFSize() { return(fsize); } public void setYear(long y) { year=y; } public long getYear() { return(year); } public void setBitrate(long b) { bitrate=b/1000; } public long getBitrate() { return(bitrate); } public void setStereo(long b) { stereo=b; } public long getStereo() { return(stereo); } public void loadInfo(String fname) { try{ this.fname=fname; File f = new File(fname); long len=f.length(); fsize=len; byte[] buf=new byte[128]; FileInputStream fis; fis = new FileInputStream(f); fis.read(buf,0,128); fis.close(); int lay=(buf[ 1 ] >> 1) & 3; int mpeg=(buf[ 1 ] >> 3) & 3; switch(mpeg) { // mpg-1.0 case 3: switch(lay) { case 3: mpeg=0; break; case 2: mpeg=1; break; case 1: mpeg=2; break; } break; // mpg-2.0 case 0: case 2: switch(lay) { case 3: mpeg=3; break; case 2: case 1: mpeg=4; break; } break; } int btr=((buf[2]>>4) & 15); setBitrate(bitRateTable[btr][mpeg]); setStereo((buf[ 3 ] >> 6) & 3); fis = new FileInputStream(f); fis.skip(len-128); fis.read(buf,0,128); setSong(new String(buf,3,29)); setArtist(new String(buf,33,30)); setAlbum(new String(buf,63,30)); try{ setYear(Long.parseLong(new String(buf,93,4))); } catch(Exception e) { setYear(2001);} fis.close(); } catch(Exception e) { System.out.println(""+e); } } } Таблица жанров: public final String[] genreNames = { "Blues", "Classic Rock", "Country", "Dance", "Disco", "Funk", "Grunge", "Hip-Hop", "Jazz", "Metal", "New Age", "Oldies", "Other", "Pop", "R&B", "Rap", "Reggae", "Rock", "Techno", "Industrial", "Alternative", "Ska", "Death Metal", "Pranks", "Soundtrack", "Euro-Techno", "Ambient", "Trip-Hop", "Vocal", "Jazz+Funk", "Fusion", "Trance", "Classical", "Instrumental", "Acid", "House", "Game", "Sound Clip", "Gospel", "Noise", "AlternRock", "Bass", "Soul", "Punk", "Space", "Meditative", "Instrumental Pop", "Instrumental Rock", "Ethnic", "Gothic", "Darkwave", "Techno-Industrial", "Electronic", "Pop-Folk", "Eurodance", "Dream", "Southern Rock", "Comedy", "Cult", "Gangsta", "Top 40", "Christian Rap", "Pop/Funk", "Jungle", "Native American", "Cabaret", "New Wave", "Psychadelic", "Rave", "Show Tune", "Trailer", "Lo-Fi", "Tribal", "Acid Punk", "Acid Jazz", "Polka", "Retro", "Musical", "Rock & Roll", "Hard Rock", };

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