Estrarre informazioni da un file MP3 con le funzioni esterne del API di Id3tag
Da Gambas-it.org - Wikipedia.
Le risorse del API di id3tag consentono anche di ottenere informazioni (Tag) dai file audio formato mp3 richiamando l'attuale versione della libreria: "libid3tag.so.0.3.0 ".
Poiché l'uso della libreria esterna libid3tag prevede il richiamo diretto ed indiretto di numerose Strutture, ed al fine di poter gestire dette Strutture esterne in modo assolutamente sicuro, ci serviremo di un'apposita libreria esterna scritta in C, che realizzeremo ad hoc all'interno del codice Gambas e che da esso richiameremo.
Il codice Gambas per la lettura di alcuni (in questo esempio) tag dei file .mp3 potrà essere il seguente:
Library "libid3tag:0.3.0" Public Struct audio_file_tags title As String artist As String album As String anno As String genere As String comment As String track As String composer As String orig_artist As String copyright As String url As String encoded_b As String End Struct Private aftag As Struct Audio_file_tags Private genre_table As String[] = ["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", "Alt. Rock", "Bass", "Soul", "Punk", "Space", "Meditative", "Instrum. Pop", "Instrum. Rock", "Ethnic", "Gothic", "Darkwave", "Techno-Indust.", "Electronic", "Pop-Folk", "Eurodance", "Dream", "Southern Rock", "Comedy", "Cult", "Gangsta", "Top 40", "Christian Rap", "Pop/Funk", "Jungle", "Native American", "Cabaret", "New Wave", "Psychadelic", "Rave", "Showtunes", "Trailer", "Lo-Fi", "Tribal", "Acid Punk", "Acid Jazz", "Polka", "Retro", "Musical", "Rock & Roll", "Hard Rock", "Folk", "Folk/Rock", "National Folk", "Swing", "Fusion", "Bebob", "Latin", "Revival", "Celtic", "Bluegrass", "Avantgarde", "Gothic Rock", "Progress. Rock", "Psychadel. 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", "Ballad", "Power Ballad", "Rhythmic Soul", "Freestyle", "Duet", "Punk Rock", "Drum Solo", "A capella", "Euro-House", "Dance Hall", "Goa", "Drum & Bass", "Club-House", "Hardcore", "Terror", "Indie", "BritPop", "Negerpunk", "Polsk Punk", "Beat", "Christian Gangsta Rap", "Heavy Metal", "Black Metal", "Crossover", "Contemporary Christian", "Christian Rock", "Merengue", "Salsa", "Thrash Metal", "Anime", "Jpop", "Synthpop"] Private Const ID3_FIELD_TYPE_STRINGLIST As Byte = 6 Private Enum ID3_FILE_MODE_READONLY = 0, ID3_FILE_MODE_READWRITE ' id3_file *id3_file_open(char const *, enum id3_file_mode) Private Extern id3_file_open(fl As String, id3_file_mode As Byte) As Pointer ' id3_tag *id3_file_tag(struct id3_file const *) Private Extern id3_file_tag(id3_file As Pointer) As Pointer ' id3_frame *id3_tag_findframe(struct id3_tag const *, char const *, unsigned int) Private Extern id3_tag_findframe(id3_tag As Pointer, id$ As String, ui As Integer) As Pointer ' id3_ucs4_t const *id3_field_getstrings(union id3_field const *, unsigned int) Private Extern id3_field_getstrings(unid3_field As Pointer, ui As Integer) As Pointer ' id3_utf8_t *id3_ucs4_utf8duplicate(id3_ucs4_t const *) Private Extern id3_ucs4_utf8duplicate(id3_ucs4_t As Pointer) As Pointer ' union id3_field *id3_frame_field(struct id3_frame const *, unsigned int) Private Extern id3_frame_field(strFrame As Pointer, ui As Integer) As Pointer ' unsigned int id3_field_getnstrings(union id3_field const *) Private Extern id3_field_getnstrings(unid3_field As Pointer) As Integer ' id3_latin1_t *id3_ucs4_latin1duplicate(id3_ucs4_t const *) Private Extern id3_ucs4_latin1duplicate(id3_ucs4_t As Pointer) As Pointer ' int id3_file_close(struct id3_file *) Private Extern id3_file_close(id3_file As Pointer) As Integer Library "/tmp/libtag3" ' Richiama la libreria ad hoc da noi realizzata per la gestione sicura delle Strutture di id3tag Private Extern obt_frame_nfields(fr As Pointer) As Integer Private Extern obt_frame_type(fr As Pointer) As Integer Private Extern obt_frame_fields(fr As Pointer) As Pointer Public Sub Main() Dim id3_file, id3_tag As Pointer Dim anno As Pointer Dim artista, titolo, album As String Dim genus, tracce, nomeFl As String Dim dur As Integer ' Verifica se già è presente la libreria ad hoc per la gestione sicura delle "Strutture" utilizzate di "id3tag", altrimenti la va a creare: If Exist("/tmp/libtag3.so") = False Then creaId3() id3_file = id3_file_open("/percorso/del/file.mp3", ID3_FILE_MODE_READONLY) If id3_file == 0 Then Error.Raise("Impossibile aprire il file !") id3_tag = id3_file_tag(id3_file) If id3_tag == 0 Then Error.Raise("Impossibile ottenere i tag del file mp3 !") With aftag artista = obtArtista(id3_tag) Print "Artista = "; artista titolo = obtTitolo(id3_tag) Print "Titolo = "; titolo anno = obtAnno(id3_tag) Print "Anno = "; String@(anno) album = obtAlbum(id3_tag) Print "Album = "; album genus = obtGenere(id3_tag) If IsDigit(genus) Then genus = genre_table[Val(genus)] Print "Genere = "; genus tracce = obtTracce(id3_tag) Print "Tracce = "; tracce nomeFl = obtOrigFilename(id3_tag) Print "Nome file originale = "; nomeFl dur = obtLen(id3_tag) Print "Durata = "; Time(0, 0, 0, dur) End With id3_file_close(id3_file) End Private Function obtArtista(id3_tag As Pointer) As String Dim nomeArtistaP As Pointer nomeArtistaP = obtFrameText(id3_tag, "TPE1") If nomeartistaP == 0 Then nomeartistaP = obtFrameText(id3_tag, "TPE2") If nomeartistaP == 0 Then nomeartistaP = obtFrameText(id3_tag, "TPE3") If nomeartistaP == 0 Then nomeartistaP = obtFrameText(id3_tag, "TPE4") If nomeartistaP == 0 Then nomeartistaP = obtFrameText(id3_tag, "TCOM") Return String@(nomeArtistaP) End Private Function obtTitolo(id3_tag As Pointer) As String Dim titoloP As Pointer titoloP = obtFrameText(id3_tag, "TIT2") Return String@(titoloP) End Private Function obtAnno(id3_tag As Pointer) As String Dim annoP As Pointer annoP = obtFrameText(id3_tag, "TYER") If annoP == 0 Then annoP = obtFrameText(id3_tag, "TDRC") Return String@(annoP) End Private Function obtAlbum(id3_tag As Pointer) As String Dim albumP As Pointer albumP = obtFrameText(id3_tag, "TALB") Return String@(albumP) End Private Function obtGenere(id3_tag As Pointer) As String Dim gnreP As Pointer gnreP = obtFrameText(id3_tag, "TCON") Return String@(gnreP) End Private Function obtTracce(id3_tag As Pointer) As String Dim tracceP As Pointer tracceP = obtFrameText(id3_tag, "TRCK") Return String@(tracceP) End Private Function obtOrigFilename(id3_tag As Pointer) As String Dim nomP As Pointer nomP = obtFrameText(id3_tag, "TOFN") Return String@(nomP) End Private Function obtLen(id3_tag As Pointer) As Integer Dim durI As Integer durI = obtDurata(id3_tag, "TLEN") Return durI End Private Function obtFrameText(tag As Pointer, id As String) As Pointer Dim frame, field1 As Pointer Dim ucs4, utf8 As Pointer frame = id3_tag_findframe(tag, id, 0) If frame == 0 Then Return 0 If obt_frame_nfields(frame) <> 2 Then Return 0 If obt_frame_type(frame) <> ID3_FIELD_TYPE_STRINGLIST Then Return 0 field1 = obt_frame_fields(frame) ucs4 = id3_field_getstrings(field1, 0) If ucs4 == 0 Then Return Null utf8 = id3_ucs4_utf8duplicate(ucs4) Return utf8 End Private Function obtDurata(tag As Pointer, id As String) As Integer Dim frame, field, latin1 As Pointer Dim nstrings, tempI As Integer Dim tempu$ As String frame = id3_tag_findframe(tag, id, 0) If frame == 0 Then Return 0 field = id3_frame_field(frame, 1) nstrings = id3_field_getnstrings(field) If nstrings <= 0 Then Return -1 latin1 = id3_ucs4_latin1duplicate(id3_field_getstrings(field, 0)) If latin1 == 0 Then Return -1 ' Il frame 'lengh' contiene la durata dei dati audio espressa in millisecondi e rappresentata in una stringa numerica: tempu$ = String@(latin1) tempI = Val(tempu$) If tempI > 0 Then Return tempI Else Return -1 Endif End ' Crea l'apposita libreria per la gestione sicura delle Strutture di "id3tag": Private Procedure creaId3() File.Save("/tmp/libtag3.c", "#include <id3tag.h>" & "\n\n" & "/* Legge nei campi delle Strutture utilizzate: */\n" & "int obt_frame_nfields(struct id3_frame *p) {\n" & " return p->nfields;\n}" & "\n\n" & "int obt_frame_type(struct id3_frame *p) {\n" & " return p->fields[1].type;\n}" & "\n\n" & "union id3_field * obt_frame_fields(struct id3_frame *p) {\n" & " return &p->fields[1];\n}") Shell "gcc -o /tmp/libtag3.so /tmp/libtag3.c -shared -fPIC" Wait End
