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<HTML>
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<HEAD>
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<TITLE>
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The libsndfile API
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</TITLE>
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<META NAME="Author" CONTENT="Erik de Castro Lopo (erikd AT mega-nerd DOT com)">
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<META NAME="Description" CONTENT="The libsndfile API.">
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<META NAME="Keywords" CONTENT="WAV AIFF AU libsndfile sound audio dsp Linux">
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<LINK REL="stylesheet" HREF="libsndfile.css" TYPE="text/css" MEDIA="all">
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<LINK REL="stylesheet" HREF="print.css" TYPE="text/css" MEDIA="print">
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</HEAD>
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<BODY>
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libsndfile
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Libsndfile is a library designed to allow the reading and writing of many
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different sampled sound file formats (such as MS Windows WAV and the Apple/SGI
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AIFF format) through one standard library interface.
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During read and write operations, formats are seamlessly converted between the
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format the application program has requested or supplied and the file's data
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format. The application programmer can remain blissfully unaware of issues
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such as file endian-ness and data format. See Note 1 and
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Note 2.
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Every effort is made to keep these documents up-to-date, error free and
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unambiguous.
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However, since maintaining the documentation is the least fun part of working
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on libsndfile, these docs can and do fall behind the behaviour of the library.
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If any errors, omissions or ambiguities are found, please notify me (erikd)
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at mega-nerd dot com.
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To supplement this reference documentation, there are simple example programs
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included in the source code tarball.
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The test suite which is also part of the source code tarball is also a good
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place to look for the correct usage of the library functions.
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Finally, if you think there is some feature missing from libsndfile, check that
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it isn't already implemented (and documented)
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here.
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Synopsis
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The functions of libsndfile are defined as follows:
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#include <stdio.h>
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#include <sndfile.h>
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SNDFILE* sf_open (const char *path, int mode, SF_INFO *sfinfo) ;
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SNDFILE* sf_wchar_open (LPCWSTR wpath, int mode, SF_INFO *sfinfo) ;
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SNDFILE* sf_open_fd (int fd, int mode, SF_INFO *sfinfo, int close_desc) ;
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SNDFILE* sf_open_virtual (SF_VIRTUAL_IO *sfvirtual, int mode, SF_INFO *sfinfo, void *user_data) ;
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int sf_format_check (const SF_INFO *info) ;
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sf_count_t sf_seek (SNDFILE *sndfile, sf_count_t frames, int whence) ;
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int sf_command (SNDFILE *sndfile, int cmd, void *data, int datasize) ;
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int sf_error (SNDFILE *sndfile) ;
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const char* sf_strerror (SNDFILE *sndfile) ;
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const char* sf_error_number (int errnum) ;
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int sf_perror (SNDFILE *sndfile) ;
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int sf_error_str (SNDFILE *sndfile, char* str, size_t len) ;
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int sf_close (SNDFILE *sndfile) ;
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void sf_write_sync (SNDFILE *sndfile) ;
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sf_count_t sf_read_short (SNDFILE *sndfile, short *ptr, sf_count_t items) ;
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sf_count_t sf_read_int (SNDFILE *sndfile, int *ptr, sf_count_t items) ;
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sf_count_t sf_read_float (SNDFILE *sndfile, float *ptr, sf_count_t items) ;
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sf_count_t sf_read_double (SNDFILE *sndfile, double *ptr, sf_count_t items) ;
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sf_count_t sf_readf_short (SNDFILE *sndfile, short *ptr, sf_count_t frames) ;
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sf_count_t sf_readf_int (SNDFILE *sndfile, int *ptr, sf_count_t frames) ;
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sf_count_t sf_readf_float (SNDFILE *sndfile, float *ptr, sf_count_t frames) ;
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sf_count_t sf_readf_double (SNDFILE *sndfile, double *ptr, sf_count_t frames) ;
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sf_count_t sf_write_short (SNDFILE *sndfile, short *ptr, sf_count_t items) ;
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sf_count_t sf_write_int (SNDFILE *sndfile, int *ptr, sf_count_t items) ;
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sf_count_t sf_write_float (SNDFILE *sndfile, float *ptr, sf_count_t items) ;
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sf_count_t sf_write_double (SNDFILE *sndfile, double *ptr, sf_count_t items) ;
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sf_count_t sf_writef_short (SNDFILE *sndfile, short *ptr, sf_count_t frames) ;
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sf_count_t sf_writef_int (SNDFILE *sndfile, int *ptr, sf_count_t frames) ;
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sf_count_t sf_writef_float (SNDFILE *sndfile, float *ptr, sf_count_t frames) ;
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sf_count_t sf_writef_double (SNDFILE *sndfile, double *ptr, sf_count_t frames) ;
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sf_count_t sf_read_raw (SNDFILE *sndfile, void *ptr, sf_count_t bytes) ;
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sf_count_t sf_write_raw (SNDFILE *sndfile, void *ptr, sf_count_t bytes) ;
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const char* sf_get_string (SNDFILE *sndfile, int str_type) ;
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int sf_set_string (SNDFILE *sndfile, int str_type, const char* str) ;
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SNDFILE* is an anonymous pointer to data which is private to the library.
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File Open Function
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SNDFILE* sf_open (const char *path, int mode, SF_INFO *sfinfo) ;
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The sf_open() function opens the sound file at the specified path.
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The filename is byte encoded, but may be utf-8 on Linux, while on Mac OS X it
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will use the filesystem character set.
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On Windows, there is also a Windows specific sf_wchar_open() that takes a
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UTF16_BE encoded filename.
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SNDFILE* sf_wchar_open (LPCWSTR wpath, int mode, SF_INFO *sfinfo) ;
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The SF_INFO structure is for passing data between the calling function and the library
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when opening a file for reading or writing. It is defined in sndfile.h as follows:
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typedef struct
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{ sf_count_t frames ; /* Used to be called samples. */
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int samplerate ;
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int channels ;
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int format ;
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int sections ;
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int seekable ;
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} SF_INFO ;
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The mode parameter for this function can be any one of the following three values:
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SFM_READ - read only mode
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SFM_WRITE - write only mode
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SFM_RDWR - read/write mode
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When opening a file for read, the format field should be set to zero before
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calling sf_open().
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The only exception to this is the case of RAW files where the caller has to set
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the samplerate, channels and format fields to valid values.
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All other fields of the structure are filled in by the library.
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When opening a file for write, the caller must fill in structure members samplerate,
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channels, and format.
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The format field in the above SF_INFO structure is made up of the bit-wise OR of a
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major format type (values between 0x10000 and 0x08000000), a minor format type
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(with values less than 0x10000) and an optional endian-ness value.
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The currently understood formats are listed in sndfile.h as follows and also include
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bitmasks for separating major and minor file types.
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Not all combinations of endian-ness and major and minor file types are valid.
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enum
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{ /* Major formats. */
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SF_FORMAT_WAV = 0x010000, /* Microsoft WAV format (little endian). */
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SF_FORMAT_AIFF = 0x020000, /* Apple/SGI AIFF format (big endian). */
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SF_FORMAT_AU = 0x030000, /* Sun/NeXT AU format (big endian). */
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SF_FORMAT_RAW = 0x040000, /* RAW PCM data. */
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SF_FORMAT_PAF = 0x050000, /* Ensoniq PARIS file format. */
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SF_FORMAT_SVX = 0x060000, /* Amiga IFF / SVX8 / SV16 format. */
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SF_FORMAT_NIST = 0x070000, /* Sphere NIST format. */
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SF_FORMAT_VOC = 0x080000, /* VOC files. */
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SF_FORMAT_IRCAM = 0x0A0000, /* Berkeley/IRCAM/CARL */
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SF_FORMAT_W64 = 0x0B0000, /* Sonic Foundry's 64 bit RIFF/WAV */
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SF_FORMAT_MAT4 = 0x0C0000, /* Matlab (tm) V4.2 / GNU Octave 2.0 */
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SF_FORMAT_MAT5 = 0x0D0000, /* Matlab (tm) V5.0 / GNU Octave 2.1 */
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SF_FORMAT_PVF = 0x0E0000, /* Portable Voice Format */
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SF_FORMAT_XI = 0x0F0000, /* Fasttracker 2 Extended Instrument */
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SF_FORMAT_HTK = 0x100000, /* HMM Tool Kit format */
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SF_FORMAT_SDS = 0x110000, /* Midi Sample Dump Standard */
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SF_FORMAT_AVR = 0x120000, /* Audio Visual Research */
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SF_FORMAT_WAVEX = 0x130000, /* MS WAVE with WAVEFORMATEX */
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SF_FORMAT_SD2 = 0x160000, /* Sound Designer 2 */
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SF_FORMAT_FLAC = 0x170000, /* FLAC lossless file format */
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SF_FORMAT_CAF = 0x180000, /* Core Audio File format */
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SF_FORMAT_WVE = 0x190000, /* Psion WVE format */
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SF_FORMAT_OGG = 0x200000, /* Xiph OGG container */
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SF_FORMAT_MPC2K = 0x210000, /* Akai MPC 2000 sampler */
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SF_FORMAT_RF64 = 0x220000, /* RF64 WAV file */
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/* Subtypes from here on. */
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SF_FORMAT_PCM_S8 = 0x0001, /* Signed 8 bit data */
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SF_FORMAT_PCM_16 = 0x0002, /* Signed 16 bit data */
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SF_FORMAT_PCM_24 = 0x0003, /* Signed 24 bit data */
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SF_FORMAT_PCM_32 = 0x0004, /* Signed 32 bit data */
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SF_FORMAT_PCM_U8 = 0x0005, /* Unsigned 8 bit data (WAV and RAW only) */
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SF_FORMAT_FLOAT = 0x0006, /* 32 bit float data */
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SF_FORMAT_DOUBLE = 0x0007, /* 64 bit float data */
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SF_FORMAT_ULAW = 0x0010, /* U-Law encoded. */
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SF_FORMAT_ALAW = 0x0011, /* A-Law encoded. */
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SF_FORMAT_IMA_ADPCM = 0x0012, /* IMA ADPCM. */
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SF_FORMAT_MS_ADPCM = 0x0013, /* Microsoft ADPCM. */
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SF_FORMAT_GSM610 = 0x0020, /* GSM 6.10 encoding. */
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SF_FORMAT_VOX_ADPCM = 0x0021, /* Oki Dialogic ADPCM encoding. */
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SF_FORMAT_G721_32 = 0x0030, /* 32kbs G721 ADPCM encoding. */
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SF_FORMAT_G723_24 = 0x0031, /* 24kbs G723 ADPCM encoding. */
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SF_FORMAT_G723_40 = 0x0032, /* 40kbs G723 ADPCM encoding. */
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SF_FORMAT_DWVW_12 = 0x0040, /* 12 bit Delta Width Variable Word encoding. */
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SF_FORMAT_DWVW_16 = 0x0041, /* 16 bit Delta Width Variable Word encoding. */
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SF_FORMAT_DWVW_24 = 0x0042, /* 24 bit Delta Width Variable Word encoding. */
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SF_FORMAT_DWVW_N = 0x0043, /* N bit Delta Width Variable Word encoding. */
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SF_FORMAT_DPCM_8 = 0x0050, /* 8 bit differential PCM (XI only) */
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SF_FORMAT_DPCM_16 = 0x0051, /* 16 bit differential PCM (XI only) */
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SF_FORMAT_VORBIS = 0x0060, /* Xiph Vorbis encoding. */
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/* Endian-ness options. */
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SF_ENDIAN_FILE = 0x00000000, /* Default file endian-ness. */
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SF_ENDIAN_LITTLE = 0x10000000, /* Force little endian-ness. */
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SF_ENDIAN_BIG = 0x20000000, /* Force big endian-ness. */
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SF_ENDIAN_CPU = 0x30000000, /* Force CPU endian-ness. */
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SF_FORMAT_SUBMASK = 0x0000FFFF,
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SF_FORMAT_TYPEMASK = 0x0FFF0000,
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SF_FORMAT_ENDMASK = 0x30000000
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} ;
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Every call to sf_open() should be matched with a call to sf_close() to free up
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memory allocated during the call to sf_open().
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On success, the sf_open function returns a non-NULL pointer which should be
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passed as the first parameter to all subsequent libsndfile calls dealing with
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that audio file.
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On fail, the sf_open function returns a NULL pointer.
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An explanation of the error can obtained by passing NULL to
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sf_strerror.
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File Descriptor Open
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SNDFILE* sf_open_fd (int fd, int mode, SF_INFO *sfinfo, int close_desc) ;
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Note: On Microsoft Windows, this function does not work if the
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application and the libsndfile DLL are linked to different versions of the
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Microsoft C runtime DLL.
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The second open function takes a file descriptor of a file that has already been
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opened.
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Care should be taken to ensure that the mode of the file represented by the
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descriptor matches the mode argument.
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This function is useful in the following circumstances:
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Opening temporary files securely (ie use the tmpfile() to return a
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FILE* pointer and then using fileno() to retrieve the file descriptor
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which is then passed to libsndfile).
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Opening files with file names using OS specific character encodings
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and then passing the file descriptor to sf_open_fd().
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Opening sound files embedded within larger files.
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More info.
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Every call to sf_open_fd() should be matched with a call to sf_close() to free up
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memory allocated during the call to sf_open().
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When sf_close() is called, the file descriptor is only closed if the close_desc
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parameter was TRUE when the sf_open_fd() function was called.
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On success, the sf_open_fd function returns a non-NULL pointer which should be
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passed as the first parameter to all subsequent libsndfile calls dealing with
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that audio file.
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On fail, the sf_open_fd function returns a NULL pointer.
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Virtual File Open Function
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SNDFILE* sf_open_virtual (SF_VIRTUAL_IO *sfvirtual, int mode, SF_INFO *sfinfo, void *user_data) ;
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Opens a soundfile from a virtual file I/O context which is provided
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by the caller. This is usually used to interface libsndfile to a stream or buffer
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based system. Apart from the sfvirtual and the user_data parameters this function behaves
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like sf_open.
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typedef struct
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{ sf_vio_get_filelen get_filelen ;
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sf_vio_seek seek ;
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sf_vio_read read ;
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sf_vio_write write ;
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sf_vio_tell tell ;
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} SF_VIRTUAL_IO ;
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Libsndfile calls the callbacks provided by the SF_VIRTUAL_IO structure when opening, reading
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and writing to the virtual file context. The user_data pointer is a user defined context which
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will be available in the callbacks.
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typedef sf_count_t (*sf_vio_get_filelen) (void *user_data) ;
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typedef sf_count_t (*sf_vio_seek) (sf_count_t offset, int whence, void *user_data) ;
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typedef sf_count_t (*sf_vio_read) (void *ptr, sf_count_t count, void *user_data) ;
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typedef sf_count_t (*sf_vio_write) (const void *ptr, sf_count_t count, void *user_data) ;
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typedef sf_count_t (*sf_vio_tell) (void *user_data) ;
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sf_vio_get_filelen
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typedef sf_count_t (*sf_vio_get_filelen) (void *user_data) ;
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The virtual file contex must return the length of the virtual file in bytes.
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sf_vio_seek
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typedef sf_count_t (*sf_vio_seek) (sf_count_t offset, int whence, void *user_data) ;
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The virtual file context must seek to offset using the seek mode provided by whence which is one of
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SEEK_CUR
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SEEK_SET
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SEEK_END
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The return value must contain the new offset in the file.
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sf_vio_read
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typedef sf_count_t (*sf_vio_read) (void *ptr, sf_count_t count, void *user_data) ;
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The virtual file context must copy ("read") "count" bytes into the
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buffer provided by ptr and return the count of actually copied bytes.
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sf_vio_write
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typedef sf_count_t (*sf_vio_write) (const void *ptr, sf_count_t count, void *user_data) ;
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The virtual file context must process "count" bytes stored in the
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buffer passed with ptr and return the count of actually processed bytes.
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sf_vio_tell
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typedef sf_count_t (*sf_vio_tell) (void *user_data) ;
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Return the current position of the virtual file context.
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Format Check Function
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int sf_format_check (const SF_INFO *info) ;
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This function allows the caller to check if a set of parameters in the SF_INFO struct
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is valid before calling sf_open (SFM_WRITE).
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sf_format_check returns TRUE if the parameters are valid and FALSE otherwise.
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File Seek Functions
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sf_count_t sf_seek (SNDFILE *sndfile, sf_count_t frames, int whence) ;
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The file seek functions work much like lseek in unistd.h with the exception that
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|
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the non-audio data is ignored and the seek only moves within the audio data section of
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|
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the file.
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|
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In addition, seeks are defined in number of (multichannel) frames.
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|
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Therefore, a seek in a stereo file from the current position forward with an offset
|
|
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of 1 would skip forward by one sample of both channels.
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like lseek(), the whence parameter can be any one of the following three values:
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SEEK_SET - The offset is set to the start of the audio data plus offset (multichannel) frames.
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SEEK_CUR - The offset is set to its current location plus offset (multichannel) frames.
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SEEK_END - The offset is set to the end of the data plus offset (multichannel) frames.
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Internally, libsndfile keeps track of the read and write locations using separate
|
|
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read and write pointers.
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|
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If a file has been opened with a mode of SFM_RDWR, bitwise OR-ing the standard whence
|
|
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values above with either SFM_READ or SFM_WRITE allows the read and write pointers to
|
|
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be modified separately.
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|
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If the SEEK_* values are used on their own, the read and write pointers are
|
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both modified.
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Note that the frames offset can be negative and in fact should be when SEEK_END is used for the
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whence parameter.
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|
|
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sf_seek will return the offset in (multichannel) frames from the start of the audio data
|
|
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or -1 if an error occured (ie an attempt is made to seek beyond the start or end of the file).
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Error Reporting Functions
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|
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int sf_error (SNDFILE *sndfile) ;
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|
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|
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|
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This function returns the current error number for the given SNDFILE.
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|
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The error number may be one of the following:
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|
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|
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|
|
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enum
|
|
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{ SF_ERR_NO_ERROR = 0,
|
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SF_ERR_UNRECOGNISED_FORMAT = 1,
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|
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SF_ERR_SYSTEM = 2,
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SF_ERR_MALFORMED_FILE = 3,
|
|
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SF_ERR_UNSUPPORTED_ENCODING = 4
|
|
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} ;
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|
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or any one of many other internal error values.
|
|
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Applications should only test the return value against error values defined in
|
|
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<sndfile.h> as the internal error values are subject to change at any
|
|
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time.
|
|
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For errors not in the above list, the function sf_error_number() can be used to
|
|
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convert it to an error string.
|
|
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|
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|
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|
|
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const char* sf_strerror (SNDFILE *sndfile) ;
|
|
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const char* sf_error_number (int errnum) ;
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|
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|
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The error functions sf_strerror() and sf_error_number() convert the library's internal
|
|
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error enumerations into text strings.
|
|
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|
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|
|
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int sf_perror (SNDFILE *sndfile) ;
|
|
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int sf_error_str (SNDFILE *sndfile, char* str, size_t len) ;
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|
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|
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The functions sf_perror() and sf_error_str() are deprecated and will be dropped
|
|
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from the library at some later date.
|
|
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File Close Function
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|
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|
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|
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int sf_close (SNDFILE *sndfile) ;
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The close function closes the file, deallocates its internal buffers and returns
|
|
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0 on success or an error value otherwise.
|
|
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Write Sync Function
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|
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|
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|
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void sf_write_sync (SNDFILE *sndfile) ;
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|
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If the file is opened SFM_WRITE or SFM_RDWR, call the operating system's function
|
|
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to force the writing of all file cache buffers to disk. If the file is opened
|
|
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SFM_READ no action is taken.
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File Read Functions
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|
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|
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sf_count_t sf_read_short (SNDFILE *sndfile, short *ptr, sf_count_t items) ;
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|
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sf_count_t sf_read_int (SNDFILE *sndfile, int *ptr, sf_count_t items) ;
|
|
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sf_count_t sf_read_float (SNDFILE *sndfile, float *ptr, sf_count_t items) ;
|
|
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sf_count_t sf_read_double (SNDFILE *sndfile, double *ptr, sf_count_t items) ;
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|
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sf_count_t sf_readf_short (SNDFILE *sndfile, short *ptr, sf_count_t frames) ;
|
|
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sf_count_t sf_readf_int (SNDFILE *sndfile, int *ptr, sf_count_t frames) ;
|
|
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sf_count_t sf_readf_float (SNDFILE *sndfile, float *ptr, sf_count_t frames) ;
|
|
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sf_count_t sf_readf_double (SNDFILE *sndfile, double *ptr, sf_count_t frames) ;
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|
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|
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The file read functions fill the array pointed to by ptr with the
|
|
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requested number of items or frames.
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|
|
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For the frames-count functions, the frames parameter specifies the number
|
|
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of frames. A frame is just a block of samples, one for each
|
|
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channel. Care must be taken to ensure that there is enough space
|
|
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4aff17 |
in the array pointed to by ptr, to take (frames * channels) number of
|
|
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items (shorts, ints, floats or doubles).
|
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|
|
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For the items-count functions, the items parameter must be an integer product
|
|
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4aff17 |
of the number of channels or an error will occur. Here, an item is just a
|
|
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sample.
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|
|
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Note: The only difference between the "items" and "frames" versions of
|
|
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each read function is the units in which the object count is specified
|
|
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- calling sf_readf_short with a count argument of N, on a SNDFILE with
|
|
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4aff17 |
C channels, is the same as calling sf_read_short with a count argument
|
|
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4aff17 |
of N*C. The buffer pointed to by "ptr" should be the same number of
|
|
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bytes in each case.
|
|
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|
|
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Note: The data type used by the calling program and the data format of
|
|
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the file do not need to be the same. For instance, it is possible to
|
|
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4aff17 |
open a 16 bit PCM encoded WAV file and read the data using
|
|
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4aff17 |
sf_read_float(). The library seamlessly converts between the two
|
|
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formats on-the-fly. See
|
|
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Note 1.
|
|
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|
|
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|
|
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|
|
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The sf_read_XXXX and sf_readf_XXXX functions return the number of
|
|
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4aff17 |
items or frames read, respectively. Unless the end of the file was
|
|
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reached during the read, the return value should equal the number of
|
|
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4aff17 |
objects requested. Attempts to read beyond the end of the file will
|
|
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not result in an error but will cause the read functions to return
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less than the number of objects requested or 0 if already at the end
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of the file.
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File Write Functions
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sf_count_t sf_write_short (SNDFILE *sndfile, short *ptr, sf_count_t items) ;
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sf_count_t sf_write_int (SNDFILE *sndfile, int *ptr, sf_count_t items) ;
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sf_count_t sf_write_float (SNDFILE *sndfile, float *ptr, sf_count_t items) ;
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sf_count_t sf_write_double (SNDFILE *sndfile, double *ptr, sf_count_t items) ;
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sf_count_t sf_writef_short (SNDFILE *sndfile, short *ptr, sf_count_t frames) ;
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sf_count_t sf_writef_int (SNDFILE *sndfile, int *ptr, sf_count_t frames) ;
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sf_count_t sf_writef_float (SNDFILE *sndfile, float *ptr, sf_count_t frames) ;
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sf_count_t sf_writef_double (SNDFILE *sndfile, double *ptr, sf_count_t frames) ;
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The file write functions write the data in the array pointed to by ptr to the file.
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For items-count functions, the items parameter specifies the size of
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the array and must be an integer product of the number of channels or
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an error will occur.
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For the frames-count functions, the array is expected to be large enough
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to hold a number of items equal to the product of frames and the
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number of channels.
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As with the read functions above, the only
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difference in the items and frames version of each write function is
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the units in which the buffer size is specified. Again, the data type
|
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used by the calling program and the data format of the file do not
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need to be the same (Note 1).
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The sf_write_XXXX and sf_writef_XXXX functions respectively return the
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number of items or frames written (which should be the same as the
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items or frames parameter).
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Raw File Read and Write Functions
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sf_count_t sf_read_raw (SNDFILE *sndfile, void *ptr, sf_count_t bytes) ;
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sf_count_t sf_write_raw (SNDFILE *sndfile, void *ptr, sf_count_t bytes) ;
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|
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Note: Unless you are writing an external decoder/encode that uses
|
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libsndfile to handle the file headers, you should not be using these
|
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functions.
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|
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The raw read and write functions read raw audio data from the audio file (not to be
|
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confused with reading RAW header-less PCM files). The number of bytes read or written
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must always be an integer multiple of the number of channels multiplied by the number
|
|
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of bytes required to represent one sample from one channel.
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The raw read and write functions return the number of bytes read or written (which
|
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should be the same as the bytes parameter).
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|
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|
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Note : The result of using of both regular reads/writes and raw reads/writes on
|
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compressed file formats other than SF_FORMAT_ALAW and SF_FORMAT_ULAW is undefined.
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|
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See also : SFC_RAW_NEEDS_ENDSWAP
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|
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|
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|
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Functions for Reading and Writing String Data
|
|
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|
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|
|
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|
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const char* sf_get_string (SNDFILE *sndfile, int str_type) ;
|
|
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int sf_set_string (SNDFILE *sndfile, int str_type, const char* str) ;
|
|
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|
|
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|
|
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|
|
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These functions allow strings to be set on files opened for write and to be
|
|
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retrieved from files opened for read where supported by the given file type.
|
|
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The str_type parameter can be any one of the following string types:
|
|
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|
|
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|
|
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|
|
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enum
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{ SF_STR_TITLE,
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SF_STR_COPYRIGHT,
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|
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SF_STR_SOFTWARE,
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|
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SF_STR_ARTIST,
|
|
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SF_STR_COMMENT,
|
|
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SF_STR_DATE,
|
|
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SF_STR_ALBUM,
|
|
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SF_STR_LICENSE,
|
|
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SF_STR_TRACKNUMBER,
|
|
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SF_STR_GENRE
|
|
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} ;
|
|
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|
|
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|
|
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|
|
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The sf_get_string() function returns the specified string if it exists and a
|
|
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NULL pointer otherwise.
|
|
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In addition to the string ids above, SF_STR_FIRST (== SF_STR_TITLE) and
|
|
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SF_STR_LAST (always the same as the highest numbers string id) are also
|
|
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available to allow iteration over all the available string ids.
|
|
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|
|
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|
|
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|
|
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The sf_set_string() function sets the string data.
|
|
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It returns zero on success and non-zero on error.
|
|
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The error code can be converted to a string using sf_error_number().
|
|
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|
|
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|
|
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|
|
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Strings passed to and retrieved from these two functions are assumed to be
|
|
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utf-8.
|
|
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However, while formats like Ogg/Vorbis and FLAC fully support utf-8, others
|
|
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like WAV and AIFF officially only support ASCII.
|
|
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Writing utf-8 strings to WAV and AIF files with libsndfile will work when read
|
|
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back with libsndfile, but may not work with other programs.
|
|
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|
|
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|
|
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|
|
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The suggested method of dealing with tags retrived using sf_get_string() is to
|
|
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assume they are utf-8.
|
|
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Similarly if you have a string in some exotic format like utf-16, it should be
|
|
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encoded to utf-8 before being written using libsndfile.
|
|
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|
|
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|
|
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|
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|
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Note 1
|
|
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|
|
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|
|
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When converting between integer PCM formats of differing size
|
|
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(e.g. using sf_read_int() to read a 16 bit PCM encoded WAV file)
|
|
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libsndfile obeys one simple rule:
|
|
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|
|
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|
|
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|
|
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Whenever integer data is moved from one sized container to another sized container,
|
|
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the most significant bit in the source container will become the most significant bit
|
|
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in the destination container.
|
|
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|
|
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|
|
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|
|
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When converting between integer data and floating point data, different rules apply.
|
|
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The default behaviour when reading floating point data (sf_read_float() or
|
|
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sf_read_double ()) from a file with integer data is normalisation. Regardless of
|
|
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whether data in the file is 8, 16, 24 or 32 bit wide, the data will be read as
|
|
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floating point data in the range [-1.0, 1.0]. Similarly, data in the range [-1.0, 1.0]
|
|
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will be written to an integer PCM file so that a data value of 1.0 will be the largest
|
|
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allowable integer for the given bit width. This normalisation can be turned on or off
|
|
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using the sf_command interface.
|
|
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|
|
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|
|
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|
|
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Note 2
|
|
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|
|
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|
|
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Reading a file containg floating point data (allowable with WAV, AIFF, AU and other
|
|
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file formats) using integer read methods (sf_read_short() or sf_read_int()) can
|
|
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produce unexpected results.
|
|
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For instance the data in the file may have a maximum absolute value < 1.0 which
|
|
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would mean that all sample values read from the file will be zero.
|
|
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In order to read these files correctly using integer read methods, it is recommended
|
|
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that you use the
|
|
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sf_command
|
|
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interface, a command of
|
|
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SFC_SET_SCALE_FLOAT_INT_READ
|
|
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and a parameter of SF_TRUE to force correct scaling.
|
|
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|
|
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|
|
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|
|
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|
|
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|
|
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The libsndfile home page is
|
|
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here.
|
|
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|
|
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|
|
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Version : 1.0.28
|
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</BODY>
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</HTML>
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