Convertire un file WAV in formato OggVorbis con le funzioni esterne del API di libvorbisfile, libvorbisenc e libogg

Per convertire un file WAV in formato VorbisOgg, è possibile utilizzare le risorse delle funzioni esterne contenute nelle librerie libvorbisfile, libvorbisenc e libogg.

Per poter fuire in Gambas di tali librerie esterne, è necessario avere installate le seguenti librerie dinamiche condivise: "libvorbisfile.so.3.3.4", "libvorbisenc.so.2.0.8" e "libogg.so.0.8.1" .

Nel semplice esempio appresso mostrato, saremo costretti a creare, inoltre, un nostra apposita libreria dinamica condivisa esterna, nella quale porre una buona parte del codice necessario per la conversione, atteso che in Gambas attualmente non è dichiarabile un tipo di valore corrispondente al "signed char", come richiesto appunto dalla parte di codice C.
Il file WAV da convertire dovrà avere le seguenti caratteristiche fondamentali: 44100 hertz, 16 bit, 2 canali.

Public Struct ogg_stream_state
  body_data As Pointer
  body_storage As Long
  body_fill As Long
  body_returned As Long
  lacing_vals As Pointer
  granule_vals As Pointer
  lacing_storage As Long
  lacing_fill As Long
  lacing_packet As Long
  lacing_returned As Long
  header[282] As Byte
  header_fill As Integer
  e_o_s As Integer
  b_o_s As Integer
  serialno As Long
  pageno As Long
  packetno As Long
  granulepos As Long
End Struct

Public Struct ogg_page
  header As Pointer
  header_len As Long
  body As Pointer
  body_len As Long
End Struct

Public Struct ogg_packet
  packet As Pointer
  bytes As Long
  b_o_s As Long
  e_o_s As Long
  granulepos As Long
  packetno As Long
End Struct

Public Struct vorbis_info
  version As Integer
  channels As Integer
  rate As Long
  bitrate_upper As Long
  bitrate_nominal As Long
  bitrate_lower As Long
  bitrate_window As Long
  codec_setup As Pointer
End Struct

Public Struct vorbis_comment
  user_comments As Pointer
  comment_lengths As Pointer
  comments As Integer
  vendor As Pointer
End Struct

Public Struct vorbis_dsp_state
  analysisp As Integer
  vi As Pointer
  pcm As Pointer
  pcmret As Pointer
  pcm_storage As Integer
  pcm_current As Integer
  pcm_returned As Integer
  preextrapolate As Integer
  eofflag As Integer
  lW As Long
  W As Long
  nW As Long
  centerW As Long
  granulepos As Long
  sequence As Long
  glue_bits As Long
  time_bits As Long
  floor_bits As Long
  res_bits As Long
End Struct

Public Struct oggpack_buffer
  endbyte As Long
  endbit As Integer
  buffer As Pointer
  ptr As Pointer
  storage As Long
End Struct

Public Struct vorbis_block
  pcm As Pointer
  opb As Struct Oggpack_buffer
  lW As Long
  W As Long
  nW As Long
  pcmend As Integer
  mode As Integer
  eofflag As Integer
  granulepos As Long
  sequence As Long
  vd As Pointer
  localstore As Pointer
  localtop As Long
  localalloc As Long
  totaluse As Long
  reap As Pointer
  glue_bits As Long
  time_bits As Long
  floor_bits As Long
  res_bits As Long
  internal As Pointer
End Struct


Library "libvorbisfile:3.3.4"
 
' void vorbis_info_init(vorbis_info *vi)
' Initializes a vorbis_info structure and allocates its internal storage.
Private Extern vorbis_info_init(vo_inf As Vorbis_info)

' void vorbis_comment_init(vorbis_comment *vc)
' Initializes a vorbis_comment structure for use.
Private Extern vorbis_comment_init(vc As Vorbis_comment)

' void vorbis_comment_add_tag(vorbis_comment *vc, const char *tag, const char *contents)
' Adds a tag-comment pair to a vorbis_comment structure.
Private Extern vorbis_comment_add_tag(vc As Vorbis_comment, tag As String, contents As String)

' int vorbis_analysis_init(vorbis_dsp_state *v,vorbis_info *vi)
' Allocates and initializes the encoder's analysis state inside a is vorbis_dsp_state.
Private Extern vorbis_analysis_init(v As Vorbis_dsp_state, vi As Vorbis_info) As Integer

' int vorbis_block_init(vorbis_dsp_state *v, vorbis_block *vb)
' Initializes a vorbis_block structure and allocates its internal storage.
Private Extern vorbis_block_init(v As Vorbis_dsp_state, vb As Vorbis_block) As Integer

' int vorbis_analysis_headerout(vorbis_dsp_state *v, vorbis_comment *vc, ogg_packet *op, ogg_packet *op_comm, ogg_packet *op_code)
' Creates and returns the three header packets needed to configure a decoder to accept compressed data.
Private Extern vorbis_analysis_headerout(v As Vorbis_dsp_state, vc As Vorbis_comment, op As Ogg_packet, op_comm As Ogg_packet, op_code As Ogg_packet) As Integer

' int vorbis_block_clear(vorbis_block *vb)
' Frees the internal storage for a vorbis_block structure.
Private Extern vorbis_block_clear(vb As Vorbis_block)

' void vorbis_dsp_clear(vorbis_dsp_state *v)
' Frees the internal storage for a vorbis_dsp_state structure.
Private Extern vorbis_dsp_clear(vd As Vorbis_dsp_state)

' void vorbis_comment_clear(vorbis_comment *vc)
' Frees the internal storage associated with a vorbis_comment structure.
Private Extern vorbis_comment_clear(vc As Vorbis_comment)

' vorbis_info_clear(vorbis_info *vi)
' Frees the internal storage for a vorbis_info structure.
Private Extern vorbis_info_clear(vi As Vorbis_info)


Library "libvorbisenc:2.0.8"

' int vorbis_encode_init_vbr(vorbis_info *vi, long channels, long rate, float base_quality)
' For setting up variable bitrate ("quality" based) modes.
Private Extern vorbis_encode_init_vbr(vi As Vorbis_info, channels As Long, rate As Long, base_quality As Single) As Integer


Library "libogg:0.8.1"

' int ogg_stream_init(ogg_stream_state *os,int serialno)
' Initialize an ogg_stream_state struct and allocates appropriate memory in preparation for encoding or decoding.
Private Extern ogg_stream_init(os As Ogg_stream_state, serialno As Integer) As Integer

' int ogg_stream_packetin(ogg_stream_state *os, ogg_packet *op)
' Submits a packet to the bitstream for page encapsulation.
Private Extern ogg_stream_packetin(os As Ogg_stream_state, op As Ogg_packet) As Integer

' int ogg_stream_flush(ogg_stream_state *os, ogg_page *og)
' checks for remaining packets inside the stream and forces remaining packets into a page, regardless of the size of the page.
Private Extern ogg_stream_flush(os As Ogg_stream_state, og As Ogg_page) As Integer

' '
' Clears and frees the internal memory used by the ogg_stream_state struct, but does not free the structure itself.
Private Extern ogg_stream_clear(os As Ogg_stream_state)

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