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704 lines
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704 lines
26 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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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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</HEAD>
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<BODY>
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<BR>
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<H1><B>libsndfile</B></H1>
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<P>
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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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</P>
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<!-- pepper -->
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<P>
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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 <A HREF="#note1">Note 1</A> and
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<A HREF="#note2">Note 2</A>.
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</P>
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<!-- pepper -->
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<P>
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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 library.
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If any errors omissions or ambiguities are found, please notify
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<A HREF="mailto:erikd@zip.com.au">
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Erik de Castro Lopo</a>.
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</P>
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<!-- pepper -->
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<P>
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<B> 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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<A HREF="command.html">here</A>.
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</B>
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</P>
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<H2><B>SYNOPSIS</B></H2>
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<P>
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The functions of libsndfile are defined as follows:
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</P>
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<!-- pepper -->
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<PRE>
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#include <stdio.h>
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#include <sndfile.h>
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SNDFILE* <A HREF="#open">sf_open</A> (const char *path, int mode, SF_INFO *sfinfo) ;
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SNDFILE* <A HREF="#open_fd">sf_open_fd</A> (int fd, int mode, SF_INFO *sfinfo, int close_desc) ;
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int <A HREF="#check">sf_format_check</A> (const SF_INFO *info) ;
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sf_count_t <A HREF="#seek">sf_seek</A> (SNDFILE *sndfile, sf_count_t frames, int whence) ;
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int <A HREF="#command">sf_command</A> (SNDFILE *sndfile, int cmd, void *data, int datasize) ;
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int <A HREF="#error">sf_error</A> (SNDFILE *sndfile) ;
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const char* <A HREF="#error">sf_strerror</A> (SNDFILE *sndfile) ;
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const char* <A HREF="#error">sf_error_number</A> (int errnum) ;
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int <A HREF="#error">sf_perror</A> (SNDFILE *sndfile) ;
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int <A HREF="#error">sf_error_str</A> (SNDFILE *sndfile, char* str, size_t len) ;
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int <A HREF="#close">sf_close</A> (SNDFILE *sndfile) ;
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void <A HREF="#write_sync">sf_write_sync</A> (SNDFILE *sndfile) ;
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sf_count_t <A HREF="#read">sf_read_short</A> (SNDFILE *sndfile, short *ptr, sf_count_t items) ;
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sf_count_t <A HREF="#read">sf_read_int</A> (SNDFILE *sndfile, int *ptr, sf_count_t items) ;
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sf_count_t <A HREF="#read">sf_read_float</A> (SNDFILE *sndfile, float *ptr, sf_count_t items) ;
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sf_count_t <A HREF="#read">sf_read_double</A> (SNDFILE *sndfile, double *ptr, sf_count_t items) ;
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sf_count_t <A HREF="#readf">sf_readf_short</A> (SNDFILE *sndfile, short *ptr, sf_count_t frames) ;
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sf_count_t <A HREF="#readf">sf_readf_int</A> (SNDFILE *sndfile, int *ptr, sf_count_t frames) ;
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sf_count_t <A HREF="#readf">sf_readf_float</A> (SNDFILE *sndfile, float *ptr, sf_count_t frames) ;
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sf_count_t <A HREF="#readf">sf_readf_double</A> (SNDFILE *sndfile, double *ptr, sf_count_t frames) ;
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sf_count_t <A HREF="#write">sf_write_short</A> (SNDFILE *sndfile, short *ptr, sf_count_t items) ;
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sf_count_t <A HREF="#write">sf_write_int</A> (SNDFILE *sndfile, int *ptr, sf_count_t items) ;
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sf_count_t <A HREF="#write">sf_write_float</A> (SNDFILE *sndfile, float *ptr, sf_count_t items) ;
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sf_count_t <A HREF="#write">sf_write_double</A> (SNDFILE *sndfile, double *ptr, sf_count_t items) ;
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sf_count_t <A HREF="#writef">sf_writef_short</A> (SNDFILE *sndfile, short *ptr, sf_count_t frames) ;
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sf_count_t <A HREF="#writef">sf_writef_int</A> (SNDFILE *sndfile, int *ptr, sf_count_t frames) ;
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sf_count_t <A HREF="#writef">sf_writef_float</A> (SNDFILE *sndfile, float *ptr, sf_count_t frames) ;
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sf_count_t <A HREF="#writef">sf_writef_double</A> (SNDFILE *sndfile, double *ptr, sf_count_t frames) ;
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sf_count_t <A HREF="#raw">sf_read_raw</A> (SNDFILE *sndfile, void *ptr, sf_count_t bytes) ;
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sf_count_t <A HREF="#raw">sf_write_raw</A> (SNDFILE *sndfile, void *ptr, sf_count_t bytes) ;
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const char* <A HREF="#string">sf_get_string</A> (SNDFILE *sndfile, int str_type) ;
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int <A HREF="#string">sf_set_string</A> (SNDFILE *sndfile, int str_type, const char* str) ;
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</PRE>
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<!-- pepper -->
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<P>
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SNDFILE* is an anonymous pointer to data which is private to the library.
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</P>
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<A NAME="open"></A>
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<H2><B>File Open Function</B></H2>
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<PRE>
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SNDFILE* sf_open (const char *path, int mode, SF_INFO *sfinfo) ;
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</PRE>
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<P>
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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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</P>
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<!-- pepper -->
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<PRE>
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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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</PRE>
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<P>
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The mode parameter for this function can be any one of the following three values:
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</P>
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<!-- pepper -->
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<PRE>
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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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</PRE>
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<P>
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When opening a file for read, the <b>format</B> 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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</P>
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<!-- pepper -->
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<P>
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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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</P>
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<!-- pepper -->
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<P>
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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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</P>
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<!-- pepper -->
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<PRE>
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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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/* 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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/* 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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</PRE>
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<!-- pepper -->
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<P>
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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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</P>
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<!-- pepper -->
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<P>
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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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</P>
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<A NAME="open_fd"></A>
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<H3><B>File Descriptor Open</B></H3>
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<PRE>
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SNDFILE* sf_open_fd (int fd, int mode, SF_INFO *sfinfo, int close_desc) ;
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</PRE>
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<P>
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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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</P>
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<UL>
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<LI>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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<LI>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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<LI>Opening sound files embedded within larger files.
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<A HREF="embedded_files.html">More info</A>.
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</UL>
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<P>
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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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</P>
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<P>
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When sf_close() is called, the file descriptor is only closed if the <B>close_desc</B>
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parameter was TRUE when the sf_open_fd() function was called.
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</P>
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<P>
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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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</P>
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<A NAME="check"></A>
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<BR><H2><B>Format Check Function</B></H2>
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<PRE>
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int sf_format_check (const SF_INFO *info) ;
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</PRE>
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<!-- pepper -->
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<P>
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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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</P>
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<P>
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sf_format_check returns TRUE if the parameters are valid and FALSE otherwise.
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</P>
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<A NAME="seek"></A>
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<BR><H2><B>File Seek Functions</B></H2>
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<PRE>
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sf_count_t sf_seek (SNDFILE *sndfile, sf_count_t frames, int whence) ;
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</PRE>
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<P>
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The file seek functions work much like lseek in unistd.h with the exception that
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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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the file.
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In addition, seeks are defined in number of (multichannel) frames.
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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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</P>
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<P>
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like lseek(), the whence parameter can be any one of the following three values:
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</P>
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<PRE>
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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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</PRE>
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<!-- pepper -->
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<P>
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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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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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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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</P>
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<P>
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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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</P>
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<P>
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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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</P>
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<A NAME="command"></A>
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<H2><BR><B>Command Interface</B></H2>
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<PRE>
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int sf_command (SNDFILE *sndfile, int cmd, void *data, int datasize) ;
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</PRE>
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<P>
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This function allows the caller to retrieve information from or change aspects of the
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library behaviour on a per file basis. Examples include reading or writing text descriptions
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to a file or changing the scaling applied to sample data during read and write.
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</P>
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<!-- pepper -->
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<P>
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The cmd parameter is a short null terminated string which specifies which command
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to execute. Data is passed to and returned from the library by use of a void
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pointer. The library will not read or write more than datasize bytes from the void
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pointer. For some calls no data is required in which case data should be NULL and
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datasize may be used for some other purpose.
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</P>
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<P>
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The return value of sf_command () depends on the value of the cmd parameter, but it is
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usually non-zero for success and zero on error.
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</P>
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<P>
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This function is explained more fully <A HREF="command.html">here</A>.
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</P>
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<A NAME="error"></A>
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<H2><BR><B>Error Reporting Functions</B></H2>
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<PRE>
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int sf_error (SNDFILE *sndfile) ;
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</PRE>
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<P>
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This function returns the current error number for the given SNDFILE.
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The error number may be one of the following:
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</P>
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<PRE>
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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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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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</PRE>
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<!-- pepper -->
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<P>
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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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</P>
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<PRE>
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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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</PRE>
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<P>
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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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</P>
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<PRE>
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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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</PRE>
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<P>
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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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</P>
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<A NAME="close"></A>
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<H2><BR><B>File Close Function</B></H2>
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<PRE>
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int sf_close (SNDFILE *sndfile) ;
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</PRE>
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<!-- pepper -->
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<P>
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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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</P>
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<BR>
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<A NAME="write_sync"></A>
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<H2><BR><B>Write Sync Function</B></H2>
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<PRE>
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void sf_write_sync (SNDFILE *sndfile) ;
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</PRE>
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<P>
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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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</P>
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<BR>
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<A NAME="read"></A>
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<H2><BR><B>File Read Functions (Items)</B></H2>
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<PRE>
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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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</PRE>
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<P>
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The file read items functions fill the array pointed to by ptr with the requested
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number of items. The items parameter must be an integer product of the number
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of channels or an error will occur.
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</P>
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<!-- pepper -->
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<P>
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It is important to note that the data type used by the calling program and the data
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format of the file do not need to be the same. For instance, it is possible to open
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a 16 bit PCM encoded WAV file and read the data using sf_read_float(). The library
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seamlessly converts between the two formats on-the-fly. See
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<A HREF="#note1">Note 1</A>.
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</P>
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<!-- pepper -->
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<P>
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The sf_read_XXXX functions return the number of items read.
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Unless the end of the file was reached during the read, the return value should
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equal the number of items requested.
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Attempts to read beyond the end of the file will not result in an error but will
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cause the sf_read_XXXX functions to return less than the number of items requested
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or 0 if already at the end of the file.
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</P>
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<A NAME="readf"></A>
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<H2><BR><B>File Read Functions (Frames)</B></H2>
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<PRE>
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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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</PRE>
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<!-- pepper -->
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<P>
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The file read frames functions fill the array pointed to by ptr with the requested
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number of frames of data. The array must be large enough to hold the product of
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frames and the number of channels.
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</P>
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<P><B>
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Care must be taken to ensure that there is enough space in the array pointed to by
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ptr, to take (frames * channels) number of items (shorts, ints, floats or doubles).
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</B></P>
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<P>
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The sf_readf_XXXX functions return the number of frames read.
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Unless the end of the file was reached during the read, the return value should equal
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the number of frames requested.
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Attempts to read beyond the end of the file will not result in an error but will cause
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the sf_readf_XXXX functions to return less than the number of frames requested or 0 if
|
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already at the end of the file.
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</P>
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|
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<A NAME="write"></A>
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<H2><BR><B>File Write Functions (Items)</B></H2>
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|
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<PRE>
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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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</PRE>
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|
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<P>
|
|
The file write items functions write the data in the array pointed to by ptr to the file.
|
|
The items parameter must be an integer product of the number of channels or an error
|
|
will occur.
|
|
</P>
|
|
<!-- pepper -->
|
|
<P>
|
|
It is important to note that the data type used by the calling program and the data
|
|
format of the file do not need to be the same. For instance, it is possible to open
|
|
a 16 bit PCM encoded WAV file and write the data using sf_write_float(). The library
|
|
seamlessly converts between the two formats on-the-fly. See
|
|
<A HREF="#note1">Note 1</A>.
|
|
</P>
|
|
<P>
|
|
The sf_write_XXXX functions return the number of items written (which should be the
|
|
same as the items parameter).
|
|
</P>
|
|
|
|
<A NAME="writef"></A>
|
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<H2><BR><B>File Write Functions (Frames)</B></H2>
|
|
|
|
<PRE>
|
|
sf_count_t sf_writef_short (SNDFILE *sndfile, short *ptr, sf_count_t frames) ;
|
|
sf_count_t sf_writef_int (SNDFILE *sndfile, int *ptr, sf_count_t frames) ;
|
|
sf_count_t sf_writef_float (SNDFILE *sndfile, float *ptr, sf_count_t frames) ;
|
|
sf_count_t sf_writef_double (SNDFILE *sndfile, double *ptr, sf_count_t frames) ;
|
|
</PRE>
|
|
|
|
<P>
|
|
The file write frames functions write the data in the array pointed to by ptr to the file.
|
|
The array must be large enough to hold the product of frames and the number of channels.
|
|
</P>
|
|
<P>
|
|
The sf_writef_XXXX functions return the number of frames written (which should be the
|
|
same as the frames parameter).
|
|
</P>
|
|
|
|
<A NAME="raw"></A>
|
|
<H2><BR><B>Raw File Read and Write Functions</B></H2>
|
|
<!-- pepper -->
|
|
<PRE>
|
|
sf_count_t sf_read_raw (SNDFILE *sndfile, void *ptr, sf_count_t bytes) ;
|
|
sf_count_t sf_write_raw (SNDFILE *sndfile, void *ptr, sf_count_t bytes) ;
|
|
</PRE>
|
|
|
|
<P>
|
|
The raw read and write functions read raw audio data from the audio file (not to be
|
|
confused with reading RAW header-less PCM files). The number of bytes read or written
|
|
must always be an integer multiple of the number of channels multiplied by the number
|
|
of bytes required to represent one sample from one channel.
|
|
</P>
|
|
<!-- pepper -->
|
|
<P>
|
|
The raw read and write functions return the number of bytes read or written (which
|
|
should be the same as the bytes parameter).
|
|
</P>
|
|
|
|
<P>
|
|
<B>
|
|
Note : The result of using of both regular reads/writes and raw reads/writes on
|
|
compressed file formats other than SF_FORMAT_ALAW and SF_FORMAT_ULAW is undefined.
|
|
</B>
|
|
</P>
|
|
|
|
<A NAME="string"></A>
|
|
<H2><BR><B>Functions for Reading and Writing String Data</B></H2>
|
|
|
|
|
|
<PRE>
|
|
const char* sf_get_string (SNDFILE *sndfile, int str_type) ;
|
|
int sf_set_string (SNDFILE *sndfile, int str_type, const char* str) ;
|
|
</PRE>
|
|
|
|
<P>
|
|
These functions allow strings to be set on files opened for write and to be
|
|
retrieved from files opened for read where supported by the given file type.
|
|
The <B>str_type</B> parameter can be any one of the following string types:
|
|
</P>
|
|
|
|
<PRE>
|
|
enum
|
|
{ SF_STR_TITLE,
|
|
SF_STR_COPYRIGHT,
|
|
SF_STR_SOFTWARE,
|
|
SF_STR_ARTIST,
|
|
SF_STR_COMMENT,
|
|
SF_STR_DATE
|
|
} ;
|
|
</PRE>
|
|
|
|
<P>
|
|
The sf_get_string() function returns the specificed string if it exists and a
|
|
NULL pointer otherwise.
|
|
In addition to the string ids above, SF_STR_FIRST (== SF_STR_TITLE) and
|
|
SF_STR_LAST (always the same as the highest numbers string id) are also
|
|
available to allow iteration over all the available string ids.
|
|
</P>
|
|
|
|
<P>
|
|
The sf_set_string() function sets the string data.
|
|
It returns zero on success and non-zero on error.
|
|
The error code can be converted to a string using sf_error_number().
|
|
</P>
|
|
|
|
|
|
<P>
|
|
|
|
</P>
|
|
|
|
<HR>
|
|
|
|
<A NAME="note1"></A>
|
|
<H2><BR><B>Note 1</B></H2>
|
|
<!-- pepper -->
|
|
<P>
|
|
When converting between integer PCM formats of differing size (ie using sf_read_int()
|
|
to read a 16 bit PCM encoded WAV file) libsndfile obeys one simple rule:
|
|
</P>
|
|
|
|
<P CLASS=indent_block>
|
|
Whenever integer data is moved from one sized container to another sized container,
|
|
the most significant bit in the source container will become the most significant bit
|
|
in the destination container.
|
|
</P>
|
|
|
|
<P>
|
|
When converting between integer data and floating point data, different rules apply.
|
|
The default behaviour when reading floating point data (sf_read_float() or
|
|
sf_read_double ()) from a file with integer data is normalisation. Regardless of
|
|
whether data in the file is 8, 16, 24 or 32 bit wide, the data will be read as
|
|
floating point data in the range [-1.0, 1.0]. Similarly, data in the range [-1.0, 1.0]
|
|
will be written to an integer PCM file so that a data value of 1.0 will be the largest
|
|
allowable integer for the given bit width. This normalisation can be turned on or off
|
|
using the <A HREF="command.html">sf_command</A> interface.
|
|
</P>
|
|
|
|
<A NAME="note2"></A>
|
|
<H2><BR><B>Note 2</B></H2>
|
|
|
|
<P>
|
|
Reading a file containg floating point data (allowable with WAV, AIFF, AU and other
|
|
file formats) using integer read methods (sf_read_short() or sf_read_int()) can
|
|
produce unexpected results.
|
|
For instance the data in the file may have a maximum absolute value < 1.0 which
|
|
would mean that all sample values read from the file will be zero.
|
|
In order to read these files correctly using integer read methods, it is recommended
|
|
that you use the
|
|
<A HREF="command.html">sf_command</A>
|
|
interface a command of
|
|
<A HREF="command.html#SFC_SET_SCALE_FLOAT_INT_READ">SFC_SET_SCALE_FLOAT_INT_READ</A>
|
|
and a parameter of SF_TRUE to force correct scaling.
|
|
</P>
|
|
<!-- pepper -->
|
|
<HR>
|
|
<!-- pepper -->
|
|
<P>
|
|
The libsndfile home page is
|
|
<A HREF="http://www.mega-nerd.com/libsndfile/">here</A>.
|
|
</P>
|
|
<P>
|
|
Version : 1.0.17
|
|
</P>
|
|
<!-- pepper -->
|
|
<!-- pepper -->
|
|
<!-- pepper -->
|
|
<!-- pepper -->
|
|
|
|
</BODY>
|
|
</HTML>
|
|
|
|
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|
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|
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|
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