Read/Write ID3 Tag information from/to MP3 files
To read or write MP3Info you can use the code bellow from Rok Krulec
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{ Description: Component MP3Info extracts/saves any ID3 Tag into/from it's properties from/to MP3 file. Keywords: MP3 ID3 TAG INFO Author: Rok Krulec Description of Variables, Properties, Methods and Events: Genres: TStrings; - List of Genres constructor Create(AOwner: TComponent); - Creates an instance destructor Destroy; override; - Destroys an instance method Save; - Saves ID3 Tag to file method RemoveID3; - Removes ID3 Tag form file property Filename: TFilename; - Filename of MP3 file, when changed it opens a new MP3 file property Artist: String; - Artist (30 Chars) property Title: String; - Title (30 Chars) property Album: String; - Album (30 Chars) property Year: String; - Year ( 4 chars) property Comment: String; - Comment (30 Chars) property Genre: String; - Genre [Read Only] Property GenreID: Byte; - Genre ID property Valid: Boolean; - Is ID3 valid [Read Only] property Saved: Boolean; - Save success [Read Only] property Error: String; - Error Message [Read Only] property onChangeFile:TNotifyEvent; - Triggers when other file is openned property onChange:TNotifyEvent; - Triggers when one of propertis is changed (Artist, Title, Album, Year, Comment, GenreID) property onError:TNotifyEvent; - Triggers when errors ocure (Wrong filename, Frong fileformat) } unit MP3Info; interface uses SysUtils, Classes; const TAGLEN = 127; type TMP3Info = class(TComponent) private { Private declarations } vFilename: TFilename; vMP3Tag, vArtist, vTitle, vAlbum, vComment, vYear, vGenre, vError: string; vGenreID: Byte; vValid: Boolean; vSaved: Boolean; vChangeFileEvent, vChangeEvent, vErrorEvent: TNotifyEvent; procedure SetFilename(Filename: TFilename); procedure SetArtist(Artist: string); procedure SetTitle(Title: string); procedure SetAlbum(Album: string); procedure SetYear(Year: string); procedure SetComment(Comment: string); procedure SetGenreID(ID: Byte); procedure Open; protected { Protected declarations } public { Public declarations } published { Published declarations } Genres: TStrings; constructor Create(AOwner: TComponent); override; destructor Destroy; override; procedure Save; procedure RemoveID3; property Filename: TFilename read vFilename write SetFilename; property Artist: string read vArtist write SetArtist; property Title: string read vTitle write SetTitle; property Album: string read vAlbum write SetAlbum; property Year: string read vYear write SetYear; property Comment: string read vComment write SetComment; property Genre: string read vGenre; property GenreID: Byte read vGenreID write SetGenreID; property Valid: Boolean read vValid; property Saved: Boolean read vSaved; property Error: string read vError; property onChangeFile: TNotifyEvent read vChangeFileEvent write vChangeFileEvent; property onChange: TNotifyEvent read vChangeEvent write vChangeEvent; property onError: TNotifyEvent read vErrorEvent write vErrorEvent; end; procedure Register; implementation constructor TMP3Info.Create(AOwner: TComponent); begin inherited Create(AOwner); Genres := TStringList.Create; vGenreID := 12; vValid := false; vSaved := false; { Fill the Genres String List so one can use it combo boxes e.t.c. Example: ComboBox.Items.Assign(MP3Info.Genres) } Genres.CommaText := '"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","Psychedelic","Rave","Showtunes","Trailer","Lo-Fi","Tribal","Acid Punk",' + '"Acid Jazz","Polka","Retro","Musical","Rock & Roll","Hard Rock","Folk","Folk/Rock","National Folk","Swing","Bebob",' + '"Latin","Revival","Celtic","Bluegrass","Avantgarde","Gothic Rock","Progressive Rock","Psychedelic Rock","Symphonic Rock",' + '"Slow Rock","Big Band","Chorus","Easy Listening","Acoustic","Humour","Speech","Chanson","Opera","Chamber Music","Sonata",' + '"Symphony","Booty Bass","Primus","Porn Groove","Satire","Slow Jam","Club","Tango","Samba","Folklore"' end; destructor TMP3Info.Destroy; begin inherited Destroy; end; { Procedure to run when Filename property is changed } procedure TMP3Info.SetFilename(Filename: TFilename); begin vFilename := Filename; Open; end; procedure TMP3Info.SetArtist(Artist: string); begin vArtist := Copy(Artist, 0, 30); if Assigned(onChange) then onChange(Self); end; procedure TMP3Info.SetTitle(Title: string); begin vTitle := Copy(Title, 0, 30); if Assigned(onChange) then onChange(Self); end; procedure TMP3Info.SetAlbum(Album: string); begin vAlbum := Copy(Album, 0, 30); if Assigned(onChange) then onChange(Self); end; procedure TMP3Info.SetYear(Year: string); begin vYear := Copy(Year, 0, 4); if Assigned(onChange) then onChange(Self); end; procedure TMP3Info.SetComment(Comment: string); begin vComment := Copy(Comment, 0, 30); if Assigned(onChange) then onChange(Self); end; procedure TMP3Info.SetGenreID(ID: Byte); begin if ((ID > 255) or (ID > Genres.Count - 1)) then ID := 12; vGenreID := ID; vGenre := Genres[vGenreID]; //this line is important because after changing //vGenreID whitout it vGenre will be the same like before !!! if Assigned(onChange) then onChange(Self); end; { Opens file with Filename property, reads ID3 Tag and sets properties } procedure TMP3Info.Open; { Strips empty spaces at the end of word } function Strip(WordToStrip: string; CharToStripAway: Char): string; var i: Integer; begin for i := length(WordToStrip) downto 1 do begin if WordToStrip[i] <> ' ' then begin Strip := Copy(WordToStrip, 0, i); exit; end; end; Strip := ''; end; var dat: file of char; id3: array[0..TAGLEN] of char; begin vSaved := false; vValid := True; if FileExists(vFilename) then begin assignfile(dat, vFilename); reset(dat); seek(dat, FileSize(dat) - 128); blockread(dat, id3, 128); closefile(dat); vMP3tag := copy(id3, 1, 3); if vMP3Tag = 'TAG' then begin vTitle := strip(copy(id3, 4, 30), ' '); vArtist := strip(copy(id3, 34, 30), ' '); vAlbum := strip(copy(id3, 64, 30), ' '); vComment := strip(copy(id3, 98, 30), ' '); vYear := strip(copy(id3, 94, 4), ' '); vGenreID := ord(id3[127]); if vGenreID > Genres.Count then vGenreID := 12; vGenre := Genres[vGenreID]; { Trigger OnChange Event } if Assigned(onChangeFile) then onChangeFile(Self); end else begin vValid := False; vTitle := ''; vArtist := ''; vAlbum := ''; vComment := ''; vYear := ''; vGenreID := 12; vError := 'Wrong file format or no ID3 Tag !'; if Assigned(onError) then onError(Self); end; end else begin vValid := False; vError := 'File doesn`t exist !'; if Assigned(onError) then onError(Self); end; end; { Removes the ID3-tag from currently open file } procedure TMP3Info.RemoveID3; var dat: file of char; begin // does the file exist ? if not FileExists(vFilename) then begin vError := 'File doesn`t exist !'; if Assigned(onError) then onError(Self); exit; end; // is the file already untagged ? if (vValid = false) then begin vError := 'File is already untagged !'; if Assigned(onError) then onError(Self); exit; end; // remove readonly-attribute if (FileGetAttr(vFilename) and faReadOnly > 0) then FileSetAttr(vFileName, FileGetAttr(vFilename) - faReadOnly); // if readonly attr. already exists it cannot be removed to cut ID3 Tag if (FileGetAttr(vFilename) and faReadOnly > 0) then begin vError := 'Cant write ID3 tag information !'; if Assigned(onError) then onError(Self); exit; end; // open current mp3 file if ID3 tag exists if (vValid = true) then begin {I-} assignfile(dat, vFilename); reset(dat); {I+} if IOResult <> 0 then begin vError := 'Could not open file !'; if Assigned(onError) then onError(Self); exit; end; seek(dat, FileSize(dat) - 128); truncate(dat); // cut all 128 bytes of file closefile(dat); vValid := false; // set vValid to false because the tag has been removed end; end; { Saves ID3 Tag to currently opened file } procedure TMP3Info.Save; { Empties 128 character array }{ Don't tell me that there is a function for this in Pascal } procedure EmptyArray(var Destination: array of char); var i: Integer; begin for i := 0 to TAGLEN do begin Destination[i] := ' '; end; end; { Insert a substring into character array at index position of array } procedure InsertToArray(Source: string; var Destination: array of char; Index: Integer); var i: Integer; begin for i := 0 to length(Source) - 1 do begin Destination[Index + i] := Source[i + 1]; end; end; var dat: file of char; id3: array[0..TAGLEN] of char; begin vSaved := true; // does the filename exist ? if FileExists(vFilename) then begin // fill 128 bytes long array with ID3 Tag information EmptyArray(id3); InsertToArray('TAG', id3, 0); InsertToArray(vTitle, id3, 3); InsertToArray(vArtist, id3, 33); InsertToArray(vAlbum, id3, 63); InsertToArray(vComment, id3, 97); InsertToArray(vYear, id3, 93); id3[127] := chr(vGenreID); // remove readonly-attribute if (FileGetAttr(vFilename) and faReadOnly > 0) then FileSetAttr(vFileName, FileGetAttr(vFilename) - faReadOnly); // if readonly attr. already exists it cannot be removed to write ID3 if (FileGetAttr(vFilename) and faReadOnly > 0) then begin vSaved := False; vError := 'Cant write ID3 tag information !'; if Assigned(onError) then onError(Self); exit; end; // if valid then overwrite existing ID3 Tag, else append to file if (vValid = True) then begin {I-} assignfile(dat, vFilename); reset(dat); seek(dat, FileSize(dat) - 128); blockwrite(dat, id3, 128); closefile(dat); {I+} if IOResult <> 0 then vSaved := false; end else begin {I-} assignfile(dat, vFilename); reset(dat); seek(dat, FileSize(dat)); blockwrite(dat, id3, 128); closefile(dat); {I+} if IOResult <> 0 then vSaved := false; end end else begin vValid := False; vSaved := False; vError := 'File doesn`t exist or is not valid !'; if Assigned(onError) then onError(Self); end; end; procedure Register; begin RegisterComponents('Samples', [TMP3Info]); end; end. |
The ID3 Information is stored in the last 128 bytes of an MP3 file.
The ID3 has the following fields, and the offsets given here, are from 0-127
Field Length offsets ————————————-
Tag 30-2
Songname 30 3-32
Artist 30 33-62
Album 30 63-92
Year 4 93-96
Comment 30 97-126
Genre 1 127