La gestione mediante le funzioni esterne dell'API di Lame
Da Gambas-it.org - Wikipedia.
Versione del 26 dic 2015 alle 19:10 di Vuott (Discussione | contributi)
LAME (LAME Ain't an Mp3 Encoder) è un codificatore MPEG Audio Layer III (mp3) di alta qualità rilasciato sotto licenza LGPL.
Convertire un file .wav in file mp3
Con le risorse dell'API di LAME è possibile realizzare facilmente un semplice applicativo capace di convertire un file audio .wav in un file audio mp3.
Per poter fruire delle risorse di LAME in Gambas, è necessario avere installata e richiamare la libreria dinamica condivisa: "libmp3lame.so.0.0.0"
Mostriamo un esempio per la conversione di un file wav a 44100 hertz, 16bit, 2 canali, nel quale si utilizzerà anche la libreria libc.so.6:
Private Const PCM_SIZE As Short = 8192 Private Const MP3_SIZE As Short = 8192 Private Const vbr_default As Byte = 4 Library "libmp3lame:0.0.0" ' lame_global_flags lame_init() ' Initialize the encoder. sets default for all encoder parameters Private Extern lame_init() As Pointer ' int lame_set_in_samplerate(lame_global_flags flags, int rate) ' Input sample rate in Hz Private Extern lame_set_in_samplerate(lame As Pointer, rate As Integer) As Integer ' int lame_set_brate(lame_global_flags flags, int brate) ' Set one of bit-rate compression ratio. Private Extern lame_set_brate(lame As Pointer, brate As Integer) As Integer ' int lame_set_VBR(lame_global_flags flags, int vbr_mode) ' Types of VBR. Private Extern lame_set_VBR(lame As Pointer, vbr As Integer) As Integer ' int lame_init_params(lame_global_flags flags) ' Sets more internal configuration based On data provided above.returns - 1 If something failed. Private Extern lame_init_params(lame As Pointer) As Integer ' int lame_encode_buffer_interleaved(lame_global_flags gfp, byte[] pcm, int num_samples, byte[] mp3buf, int mp3buf_size) ' This is a convenience method using byte[] array instead of short[], the byte[] buffer used must be 2x the length of the analogous short[] version. ' Input has L & R channel data interleaved. NOTE: num_samples = number of samples in the L (or R) channel, not the total number of samples in pcm[] Private Extern lame_encode_buffer_interleaved(lame As Pointer, pcm As Pointer, num_samples As Integer, mp3buf As Pointer, mp3buf_size As Integer) As Integer ' int lame_encode_flush(lame_global_flags gfp, unsigned char* mp3buf, Int size) ' lame_encode_flush will flush the intenal PCM buffers. ' "mp3buf" should be at least 7200 bytes long to hold all possible emitted data. Private Extern lame_encode_flush(lame As Pointer, mp3buf As Pointer, size As Integer) As Integer ' int lame_close(lame_global_flags flags) ' Final call to fFree all remaining buffers. Private Extern lame_close(lame As Pointer) As Integer Library "libc:6" ' FILE *fopen (const char *__restrict __filename, const char *__restrict __modes) ' Open a file and create a new stream for it. Private Extern fopen(filename As String, modes As String) As Pointer ' size_t fread (void *__restrict __ptr, size_t __size, size_t __n, FILE *__restrict __stream) ' Read chunks of generic data from STREAM. Private Extern fread(ptr As Pointer, size As Long, n As Long, sFl As Pointer) As Long ' size_t fwrite (const void *__restrict __ptr, size_t __size, size_t __n, FILE *__restrict __s) ' Write chunks of generic data to STREAM. Private Extern fwrite(ptr As Pointer, size As Long, n As Long, sFl As Pointer) As Long ' int fclose (FILE *__stream) ' Close STREAM. Private Extern fclose(sFl As Pointer) As Integer Public Sub Main() Dim letto, scritto As Long Dim pcm, mp3, handle, pcm_buffer, mp3_buffer As Pointer pcm_buffer = Alloc(PCM_SIZE * 4) mp3_buffer = Alloc(MP3_SIZE) pcm = fopen("percorso_del_file.wav", "rb") mp3 = fopen("percorso_del_file.mp3", "wb") ' La libreria va innanzitutto inizializzata: handle = lame_init() ' L'inizializzazione imposta i parametri con valori predefiniti. ' E' possibile modificare tali valori con apposite funzioni del tipo "lame_set_*()": lame_set_in_samplerate(handle, 44100) lame_set_brate(handle, 128) lame_set_VBR(handle, vbr_default) ' Dopo aver impostato i parametri, si controlla che tutto sia a posto mediante la funzione: lame_init_params(handle) Do ' Si legge dal file .wav: letto = fread(pcm_buffer, 2 * SizeOf(gb.Short), PCM_SIZE, pcm) If letto = 0 Then scritto = lame_encode_flush(handle, mp3_buffer, MP3_SIZE) Else scritto = lame_encode_buffer_interleaved(handle, pcm_buffer, letto, mp3_buffer, MP3_SIZE) ' Si scrivono i dati codificati in mpeg nel file di destinazione: fwrite(mp3_buffer, scritto, 1, mp3) Endif Loop While letto <> 0 ' Libera le due aree allocate; chiude l'handle della libreria e i due file: Free(pcm_buffer) Free(mp3_buffer) lame_close(handle) fclose(mp3) fclose(pcm) End
Nello stesso esempio potremo ridurre le funzioni a quelle sole strettamente appartenenti all'API di LAME:
Private Const vbr_default As Byte = 4 Library "libmp3lame:0.0.0" ' lame_global_flags lame_init() Private Extern lame_init() As Pointer ' int lame_set_in_samplerate(lame_global_flags flags, int rate) Private Extern lame_set_in_samplerate(lame As Pointer, rate As Integer) As Integer ' int lame_set_brate(lame_global_flags flags, int brate) Private Extern lame_set_brate(lame As Pointer, brate As Integer) As Integer ' int lame_set_VBR(lame_global_flags flags, int vbr_mode) Private Extern lame_set_VBR(lame As Pointer, vbr As Integer) As Integer ' int lame_init_params(lame_global_flags flags) Private Extern lame_init_params(lame As Pointer) As Integer ' int lame_encode_buffer_interleaved(lame_global_flags gfp, byte[] pcm, int num_samples, byte[] mp3buf, int mp3buf_size) Private Extern lame_encode_buffer_interleaved(lame As Pointer, pcm As Byte[], num_samples As Integer, mp3buf As Byte[], mp3buf_size As Integer) As Integer ' int lame_encode_flush(lame_global_flags gfp, unsigned char* mp3buf, Int size) Private Extern lame_encode_flush(lame As Pointer, mp3buf As Byte[], size As Integer) As Integer ' int lame_close(lame_global_flags flags) Private Extern lame_close(lame As Pointer) As Integer Public Sub Main() Dim handle As Pointer Dim pcm, mp3 As File Dim percorsoFile As String = "/percorso/del/file.wav" Dim scritto, campioni, dimensione As Integer Dim pcm_buffer, mp3_buffer As Byte[] pcm = Open percorsoFile For Read mp3 = Open "/percorso/del/nuovo/file.mp3" For Create dimensione = CInt(Stat(percorsoFile).Size) mp3_buffer = New Byte[dimensione] campioni = dimensione \ 4 ' Il decodificatore necessita di essere inizializzato: handle = lame_init() ' L'inizializzazione imposta i parametri con valori predefiniti. ' E' possibile modificare tali valori con apposite funzioni del tipo "lame_set_*()": lame_set_in_samplerate(handle, 44100) lame_set_brate(handle, 128) lame_set_VBR(handle, vbr_default) ' Dopo aver impostato i parametri, si controlla che tutto sia a posto mediante la funzione: lame_init_params(handle) With pcm_buffer = New Byte[](Lof(pcm)) .Read(pcm, 0, Lof(pcm)) End With scritto = lame_encode_buffer_interleaved(handle, pcm_buffer, campioni, mp3_buffer, dimensione) mp3_buffer.Write(mp3, 0, scritto) scritto = lame_encode_flush(handle, mp3_buffer, dimensione) ' Chiude l'handle della libreria e i due file: lame_close(handle) mp3.Close pcm.Close End
Riferimenti
- Il sito dell'API di LAME