Mercurial > hg > sv-dependency-builds
diff src/libsndfile-1.0.27/doc/api.html @ 40:1df64224f5ac
Current libsndfile source
| author | Chris Cannam |
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| date | Tue, 18 Oct 2016 13:22:47 +0100 |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/src/libsndfile-1.0.27/doc/api.html Tue Oct 18 13:22:47 2016 +0100 @@ -0,0 +1,810 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> +<HTML> + +<HEAD> + <TITLE> + The libsndfile API + </TITLE> + <META NAME="Author" CONTENT="Erik de Castro Lopo (erikd AT mega-nerd DOT com)"> + <META NAME="Description" CONTENT="The libsndfile API."> + <META NAME="Keywords" CONTENT="WAV AIFF AU libsndfile sound audio dsp Linux"> + <LINK REL="stylesheet" HREF="libsndfile.css" TYPE="text/css" MEDIA="all"> + <LINK REL="stylesheet" HREF="print.css" TYPE="text/css" MEDIA="print"> +</HEAD> + +<BODY> + +<BR> +<H1><B>libsndfile</B></H1> +<P> + Libsndfile is a library designed to allow the reading and writing of many + different sampled sound file formats (such as MS Windows WAV and the Apple/SGI + AIFF format) through one standard library interface. +</P> +<!-- pepper --> +<P> + During read and write operations, formats are seamlessly converted between the + format the application program has requested or supplied and the file's data + format. The application programmer can remain blissfully unaware of issues + such as file endian-ness and data format. See <A HREF="#note1">Note 1</A> and + <A HREF="#note2">Note 2</A>. +</P> +<!-- pepper --> +<P> + Every effort is made to keep these documents up-to-date, error free and + unambiguous. + However, since maintaining the documentation is the least fun part of working + on libsndfile, these docs can and do fall behind the behaviour of the library. + If any errors, omissions or ambiguities are found, please notify me (erikd) + at mega-nerd dot com. +</P> +<!-- pepper --> +<P> + To supplement this reference documentation, there are simple example programs + included in the source code tarball. + The test suite which is also part of the source code tarball is also a good + place to look for the correct usage of the library functions. +</P> +<!-- pepper --> +<P> + <B> Finally, if you think there is some feature missing from libsndfile, check that + it isn't already implemented (and documented) + <A HREF="command.html">here</A>. + </B> +</P> + +<H2><B>Synopsis</B></H2> +<P> +The functions of libsndfile are defined as follows: +</P> +<!-- pepper --> +<PRE> + #include <stdio.h> + #include <sndfile.h> + + SNDFILE* <A HREF="#open">sf_open</A> (const char *path, int mode, SF_INFO *sfinfo) ; + SNDFILE* <A HREF="#open">sf_wchar_open</A> (LPCWSTR wpath, int mode, SF_INFO *sfinfo) ; + SNDFILE* <A HREF="#open_fd">sf_open_fd</A> (int fd, int mode, SF_INFO *sfinfo, int close_desc) ; + SNDFILE* <A HREF="#open_virtual">sf_open_virtual</A> (SF_VIRTUAL_IO *sfvirtual, int mode, SF_INFO *sfinfo, void *user_data) ; + int <A HREF="#check">sf_format_check</A> (const SF_INFO *info) ; + + sf_count_t <A HREF="#seek">sf_seek</A> (SNDFILE *sndfile, sf_count_t frames, int whence) ; + + int <A HREF="command.html">sf_command</A> (SNDFILE *sndfile, int cmd, void *data, int datasize) ; + + int <A HREF="#error">sf_error</A> (SNDFILE *sndfile) ; + const char* <A HREF="#error">sf_strerror</A> (SNDFILE *sndfile) ; + const char* <A HREF="#error">sf_error_number</A> (int errnum) ; + + int <A HREF="#error">sf_perror</A> (SNDFILE *sndfile) ; + int <A HREF="#error">sf_error_str</A> (SNDFILE *sndfile, char* str, size_t len) ; + + int <A HREF="#close">sf_close</A> (SNDFILE *sndfile) ; + void <A HREF="#write_sync">sf_write_sync</A> (SNDFILE *sndfile) ; + + sf_count_t <A HREF="#read">sf_read_short</A> (SNDFILE *sndfile, short *ptr, sf_count_t items) ; + sf_count_t <A HREF="#read">sf_read_int</A> (SNDFILE *sndfile, int *ptr, sf_count_t items) ; + sf_count_t <A HREF="#read">sf_read_float</A> (SNDFILE *sndfile, float *ptr, sf_count_t items) ; + sf_count_t <A HREF="#read">sf_read_double</A> (SNDFILE *sndfile, double *ptr, sf_count_t items) ; + + sf_count_t <A HREF="#readf">sf_readf_short</A> (SNDFILE *sndfile, short *ptr, sf_count_t frames) ; + sf_count_t <A HREF="#readf">sf_readf_int</A> (SNDFILE *sndfile, int *ptr, sf_count_t frames) ; + sf_count_t <A HREF="#readf">sf_readf_float</A> (SNDFILE *sndfile, float *ptr, sf_count_t frames) ; + sf_count_t <A HREF="#readf">sf_readf_double</A> (SNDFILE *sndfile, double *ptr, sf_count_t frames) ; + + sf_count_t <A HREF="#write">sf_write_short</A> (SNDFILE *sndfile, short *ptr, sf_count_t items) ; + sf_count_t <A HREF="#write">sf_write_int</A> (SNDFILE *sndfile, int *ptr, sf_count_t items) ; + sf_count_t <A HREF="#write">sf_write_float</A> (SNDFILE *sndfile, float *ptr, sf_count_t items) ; + sf_count_t <A HREF="#write">sf_write_double</A> (SNDFILE *sndfile, double *ptr, sf_count_t items) ; + + sf_count_t <A HREF="#writef">sf_writef_short</A> (SNDFILE *sndfile, short *ptr, sf_count_t frames) ; + sf_count_t <A HREF="#writef">sf_writef_int</A> (SNDFILE *sndfile, int *ptr, sf_count_t frames) ; + sf_count_t <A HREF="#writef">sf_writef_float</A> (SNDFILE *sndfile, float *ptr, sf_count_t frames) ; + sf_count_t <A HREF="#writef">sf_writef_double</A> (SNDFILE *sndfile, double *ptr, sf_count_t frames) ; + + sf_count_t <A HREF="#raw">sf_read_raw</A> (SNDFILE *sndfile, void *ptr, sf_count_t bytes) ; + sf_count_t <A HREF="#raw">sf_write_raw</A> (SNDFILE *sndfile, void *ptr, sf_count_t bytes) ; + + const char* <A HREF="#string">sf_get_string</A> (SNDFILE *sndfile, int str_type) ; + int <A HREF="#string">sf_set_string</A> (SNDFILE *sndfile, int str_type, const char* str) ; + +</PRE> +<!-- pepper --> +<P> +SNDFILE* is an anonymous pointer to data which is private to the library. +</P> + + +<A NAME="open"></A> +<H2><B>File Open Function</B></H2> + +<PRE> + SNDFILE* sf_open (const char *path, int mode, SF_INFO *sfinfo) ; +</PRE> + +<P> +The sf_open() function opens the sound file at the specified path. +The filename is byte encoded, but may be utf-8 on Linux, while on Mac OS X it +will use the filesystem character set. +On Windows, there is also a Windows specific sf_wchar_open() that takes a +UTF16_BE encoded filename. +</P> + +<PRE> + SNDFILE* sf_wchar_open (LPCWSTR wpath, int mode, SF_INFO *sfinfo) ; +</PRE> + +<P> +The SF_INFO structure is for passing data between the calling function and the library +when opening a file for reading or writing. It is defined in sndfile.h as follows: +</P> +<!-- pepper --> +<PRE> + typedef struct + { sf_count_t frames ; /* Used to be called samples. */ + int samplerate ; + int channels ; + int format ; + int sections ; + int seekable ; + } SF_INFO ; +</PRE> + +<P> +The mode parameter for this function can be any one of the following three values: +</P> +<!-- pepper --> +<PRE> + SFM_READ - read only mode + SFM_WRITE - write only mode + SFM_RDWR - read/write mode +</PRE> + +<P> +When opening a file for read, the <b>format</B> field should be set to zero before +calling sf_open(). +The only exception to this is the case of RAW files where the caller has to set +the samplerate, channels and format fields to valid values. +All other fields of the structure are filled in by the library. +</P> +<!-- pepper --> +<P> +When opening a file for write, the caller must fill in structure members samplerate, +channels, and format. +</P> +<!-- pepper --> +<P> +The format field in the above SF_INFO structure is made up of the bit-wise OR of a +major format type (values between 0x10000 and 0x08000000), a minor format type +(with values less than 0x10000) and an optional endian-ness value. +The currently understood formats are listed in sndfile.h as follows and also include +bitmasks for separating major and minor file types. +Not all combinations of endian-ness and major and minor file types are valid. +</P> +<!-- pepper --> +<PRE> + enum + { /* Major formats. */ + SF_FORMAT_WAV = 0x010000, /* Microsoft WAV format (little endian). */ + SF_FORMAT_AIFF = 0x020000, /* Apple/SGI AIFF format (big endian). */ + SF_FORMAT_AU = 0x030000, /* Sun/NeXT AU format (big endian). */ + SF_FORMAT_RAW = 0x040000, /* RAW PCM data. */ + SF_FORMAT_PAF = 0x050000, /* Ensoniq PARIS file format. */ + SF_FORMAT_SVX = 0x060000, /* Amiga IFF / SVX8 / SV16 format. */ + SF_FORMAT_NIST = 0x070000, /* Sphere NIST format. */ + SF_FORMAT_VOC = 0x080000, /* VOC files. */ + SF_FORMAT_IRCAM = 0x0A0000, /* Berkeley/IRCAM/CARL */ + SF_FORMAT_W64 = 0x0B0000, /* Sonic Foundry's 64 bit RIFF/WAV */ + SF_FORMAT_MAT4 = 0x0C0000, /* Matlab (tm) V4.2 / GNU Octave 2.0 */ + SF_FORMAT_MAT5 = 0x0D0000, /* Matlab (tm) V5.0 / GNU Octave 2.1 */ + SF_FORMAT_PVF = 0x0E0000, /* Portable Voice Format */ + SF_FORMAT_XI = 0x0F0000, /* Fasttracker 2 Extended Instrument */ + SF_FORMAT_HTK = 0x100000, /* HMM Tool Kit format */ + SF_FORMAT_SDS = 0x110000, /* Midi Sample Dump Standard */ + SF_FORMAT_AVR = 0x120000, /* Audio Visual Research */ + SF_FORMAT_WAVEX = 0x130000, /* MS WAVE with WAVEFORMATEX */ + SF_FORMAT_SD2 = 0x160000, /* Sound Designer 2 */ + SF_FORMAT_FLAC = 0x170000, /* FLAC lossless file format */ + SF_FORMAT_CAF = 0x180000, /* Core Audio File format */ + SF_FORMAT_WVE = 0x190000, /* Psion WVE format */ + SF_FORMAT_OGG = 0x200000, /* Xiph OGG container */ + SF_FORMAT_MPC2K = 0x210000, /* Akai MPC 2000 sampler */ + SF_FORMAT_RF64 = 0x220000, /* RF64 WAV file */ + + /* Subtypes from here on. */ + + SF_FORMAT_PCM_S8 = 0x0001, /* Signed 8 bit data */ + SF_FORMAT_PCM_16 = 0x0002, /* Signed 16 bit data */ + SF_FORMAT_PCM_24 = 0x0003, /* Signed 24 bit data */ + SF_FORMAT_PCM_32 = 0x0004, /* Signed 32 bit data */ + + SF_FORMAT_PCM_U8 = 0x0005, /* Unsigned 8 bit data (WAV and RAW only) */ + + SF_FORMAT_FLOAT = 0x0006, /* 32 bit float data */ + SF_FORMAT_DOUBLE = 0x0007, /* 64 bit float data */ + + SF_FORMAT_ULAW = 0x0010, /* U-Law encoded. */ + SF_FORMAT_ALAW = 0x0011, /* A-Law encoded. */ + SF_FORMAT_IMA_ADPCM = 0x0012, /* IMA ADPCM. */ + SF_FORMAT_MS_ADPCM = 0x0013, /* Microsoft ADPCM. */ + + SF_FORMAT_GSM610 = 0x0020, /* GSM 6.10 encoding. */ + SF_FORMAT_VOX_ADPCM = 0x0021, /* Oki Dialogic ADPCM encoding. */ + + SF_FORMAT_G721_32 = 0x0030, /* 32kbs G721 ADPCM encoding. */ + SF_FORMAT_G723_24 = 0x0031, /* 24kbs G723 ADPCM encoding. */ + SF_FORMAT_G723_40 = 0x0032, /* 40kbs G723 ADPCM encoding. */ + + SF_FORMAT_DWVW_12 = 0x0040, /* 12 bit Delta Width Variable Word encoding. */ + SF_FORMAT_DWVW_16 = 0x0041, /* 16 bit Delta Width Variable Word encoding. */ + SF_FORMAT_DWVW_24 = 0x0042, /* 24 bit Delta Width Variable Word encoding. */ + SF_FORMAT_DWVW_N = 0x0043, /* N bit Delta Width Variable Word encoding. */ + + SF_FORMAT_DPCM_8 = 0x0050, /* 8 bit differential PCM (XI only) */ + SF_FORMAT_DPCM_16 = 0x0051, /* 16 bit differential PCM (XI only) */ + + SF_FORMAT_VORBIS = 0x0060, /* Xiph Vorbis encoding. */ + + /* Endian-ness options. */ + + SF_ENDIAN_FILE = 0x00000000, /* Default file endian-ness. */ + SF_ENDIAN_LITTLE = 0x10000000, /* Force little endian-ness. */ + SF_ENDIAN_BIG = 0x20000000, /* Force big endian-ness. */ + SF_ENDIAN_CPU = 0x30000000, /* Force CPU endian-ness. */ + + SF_FORMAT_SUBMASK = 0x0000FFFF, + SF_FORMAT_TYPEMASK = 0x0FFF0000, + SF_FORMAT_ENDMASK = 0x30000000 + } ; +</PRE> +<!-- pepper --> +<P> +Every call to sf_open() should be matched with a call to sf_close() to free up +memory allocated during the call to sf_open(). +</P> +<!-- pepper --> +<P> +On success, the sf_open function returns a non-NULL pointer which should be +passed as the first parameter to all subsequent libsndfile calls dealing with +that audio file. +On fail, the sf_open function returns a NULL pointer. +An explanation of the error can obtained by passing NULL to + <A HREF="#error">sf_strerror</A>. +</P> + +<A NAME="open_fd"></A> +<H3><B>File Descriptor Open</B></H3> + +<PRE> + SNDFILE* sf_open_fd (int fd, int mode, SF_INFO *sfinfo, int close_desc) ; +</PRE> + +<P> +<b>Note:</b> On Microsoft Windows, this function does not work if the +application and the libsndfile DLL are linked to different versions of the +Microsoft C runtime DLL. +</P> +<P> +The second open function takes a file descriptor of a file that has already been +opened. +Care should be taken to ensure that the mode of the file represented by the +descriptor matches the mode argument. +This function is useful in the following circumstances: +</P> + +<UL> + <LI>Opening temporary files securely (ie use the tmpfile() to return a + FILE* pointer and then using fileno() to retrieve the file descriptor + which is then passed to libsndfile). + <LI>Opening files with file names using OS specific character encodings + and then passing the file descriptor to sf_open_fd(). + <LI>Opening sound files embedded within larger files. + <A HREF="embedded_files.html">More info</A>. +</UL> + +<P> +Every call to sf_open_fd() should be matched with a call to sf_close() to free up +memory allocated during the call to sf_open(). +</P> + +<P> +When sf_close() is called, the file descriptor is only closed if the <B>close_desc</B> +parameter was TRUE when the sf_open_fd() function was called. +</P> + +<P> +On success, the sf_open_fd function returns a non-NULL pointer which should be +passed as the first parameter to all subsequent libsndfile calls dealing with +that audio file. +On fail, the sf_open_fd function returns a NULL pointer. +</P> + +<A NAME="open_virtual"></A> +<h3><b>Virtual File Open Function</b></h3> +<pre> + SNDFILE* sf_open_virtual (SF_VIRTUAL_IO *sfvirtual, int mode, SF_INFO *sfinfo, void *user_data) ; +</pre> +<p> + Opens a soundfile from a virtual file I/O context which is provided + by the caller. This is usually used to interface libsndfile to a stream or buffer + based system. Apart from the sfvirtual and the user_data parameters this function behaves + like <a href="#open">sf_open</a>. +</p> + +<pre> + typedef struct + { sf_vio_get_filelen get_filelen ; + sf_vio_seek seek ; + sf_vio_read read ; + sf_vio_write write ; + sf_vio_tell tell ; + } SF_VIRTUAL_IO ; +</pre> +<p> +Libsndfile calls the callbacks provided by the SF_VIRTUAL_IO structure when opening, reading +and writing to the virtual file context. The user_data pointer is a user defined context which +will be available in the callbacks. +</p> +<pre> + typedef sf_count_t (*sf_vio_get_filelen) (void *user_data) ; + typedef sf_count_t (*sf_vio_seek) (sf_count_t offset, int whence, void *user_data) ; + typedef sf_count_t (*sf_vio_read) (void *ptr, sf_count_t count, void *user_data) ; + typedef sf_count_t (*sf_vio_write) (const void *ptr, sf_count_t count, void *user_data) ; + typedef sf_count_t (*sf_vio_tell) (void *user_data) ; +</pre> +<h4>sf_vio_get_filelen</h4> +<pre> + typedef sf_count_t (*sf_vio_get_filelen) (void *user_data) ; +</pre> +<p> +The virtual file contex must return the length of the virtual file in bytes.<br> +</p> +<h4>sf_vio_seek</h4> +<pre> + typedef sf_count_t (*sf_vio_seek) (sf_count_t offset, int whence, void *user_data) ; +</pre> +<p> +The virtual file context must seek to offset using the seek mode provided by whence which is one of<br> +</p> +<pre> + SEEK_CUR + SEEK_SET + SEEK_END +</pre> +<p> +The return value must contain the new offset in the file. +</p> +<h4>sf_vio_read</h4> +<pre> + typedef sf_count_t (*sf_vio_read) (void *ptr, sf_count_t count, void *user_data) ; +</pre> +<p> +The virtual file context must copy ("read") "count" bytes into the +buffer provided by ptr and return the count of actually copied bytes. +</p> +<h4>sf_vio_write</h4> +<pre> + typedef sf_count_t (*sf_vio_write) (const void *ptr, sf_count_t count, void *user_data) ; +</pre> +<p> +The virtual file context must process "count" bytes stored in the +buffer passed with ptr and return the count of actually processed bytes.<br> +</p> +<h4>sf_vio_tell</h4> +<pre> + typedef sf_count_t (*sf_vio_tell) (void *user_data) ; +</pre> +<p> +Return the current position of the virtual file context.<br> +</p> + + +<A NAME="check"></A> +<BR><H2><B>Format Check Function</B></H2> + +<PRE> + int sf_format_check (const SF_INFO *info) ; +</PRE> +<!-- pepper --> +<P> +This function allows the caller to check if a set of parameters in the SF_INFO struct +is valid before calling sf_open (SFM_WRITE). +</P> +<P> +sf_format_check returns TRUE if the parameters are valid and FALSE otherwise. +</P> + +<A NAME="seek"></A> +<BR><H2><B>File Seek Functions</B></H2> + +<PRE> + sf_count_t sf_seek (SNDFILE *sndfile, sf_count_t frames, int whence) ; +</PRE> + +<P> +The file seek functions work much like lseek in unistd.h with the exception that +the non-audio data is ignored and the seek only moves within the audio data section of +the file. +In addition, seeks are defined in number of (multichannel) frames. +Therefore, a seek in a stereo file from the current position forward with an offset +of 1 would skip forward by one sample of both channels. +</P> + +<P> +like lseek(), the whence parameter can be any one of the following three values: +</P> + +<PRE> + SEEK_SET - The offset is set to the start of the audio data plus offset (multichannel) frames. + SEEK_CUR - The offset is set to its current location plus offset (multichannel) frames. + SEEK_END - The offset is set to the end of the data plus offset (multichannel) frames. +</PRE> +<!-- pepper --> +<P> +Internally, libsndfile keeps track of the read and write locations using separate +read and write pointers. +If a file has been opened with a mode of SFM_RDWR, bitwise OR-ing the standard whence +values above with either SFM_READ or SFM_WRITE allows the read and write pointers to +be modified separately. +If the SEEK_* values are used on their own, the read and write pointers are +both modified. +</P> + +<P> +Note that the frames offset can be negative and in fact should be when SEEK_END is used for the +whence parameter. +</P> +<P> +sf_seek will return the offset in (multichannel) frames from the start of the audio data +or -1 if an error occured (ie an attempt is made to seek beyond the start or end of the file). +</P> + +<A NAME="error"></A> +<H2><BR><B>Error Reporting Functions</B></H2> + + +<PRE> + int sf_error (SNDFILE *sndfile) ; +</PRE> +<P> +This function returns the current error number for the given SNDFILE. +The error number may be one of the following: +</P> +<PRE> + enum + { SF_ERR_NO_ERROR = 0, + SF_ERR_UNRECOGNISED_FORMAT = 1, + SF_ERR_SYSTEM = 2, + SF_ERR_MALFORMED_FILE = 3, + SF_ERR_UNSUPPORTED_ENCODING = 4 + } ; +</PRE> +<!-- pepper --> +<P> +or any one of many other internal error values. +Applications should only test the return value against error values defined in +<sndfile.h> as the internal error values are subject to change at any +time. +For errors not in the above list, the function sf_error_number() can be used to +convert it to an error string. +</P> + +<PRE> + const char* sf_strerror (SNDFILE *sndfile) ; + const char* sf_error_number (int errnum) ; +</PRE> + +<P> +The error functions sf_strerror() and sf_error_number() convert the library's internal +error enumerations into text strings. +</P> +<PRE> + int sf_perror (SNDFILE *sndfile) ; + int sf_error_str (SNDFILE *sndfile, char* str, size_t len) ; +</PRE> + +<P> +The functions sf_perror() and sf_error_str() are deprecated and will be dropped +from the library at some later date. +</P> + +<A NAME="close"></A> +<H2><BR><B>File Close Function</B></H2> + +<PRE> + int sf_close (SNDFILE *sndfile) ; +</PRE> +<!-- pepper --> +<P> +The close function closes the file, deallocates its internal buffers and returns +0 on success or an error value otherwise. +</P> +<BR> + +<A NAME="write_sync"></A> +<H2><BR><B>Write Sync Function</B></H2> + +<PRE> + void sf_write_sync (SNDFILE *sndfile) ; +</PRE> +<!-- pepper --> +<P> +If the file is opened SFM_WRITE or SFM_RDWR, call the operating system's function +to force the writing of all file cache buffers to disk. If the file is opened +SFM_READ no action is taken. +</P> +<BR> + + +<A NAME="read"></A> +<H2><BR><B>File Read Functions</B></H2> + +<PRE> + sf_count_t sf_read_short (SNDFILE *sndfile, short *ptr, sf_count_t items) ; + sf_count_t sf_read_int (SNDFILE *sndfile, int *ptr, sf_count_t items) ; + sf_count_t sf_read_float (SNDFILE *sndfile, float *ptr, sf_count_t items) ; + sf_count_t sf_read_double (SNDFILE *sndfile, double *ptr, sf_count_t items) ; +</PRE> + +<A NAME="readf"></A> +<PRE> + sf_count_t sf_readf_short (SNDFILE *sndfile, short *ptr, sf_count_t frames) ; + sf_count_t sf_readf_int (SNDFILE *sndfile, int *ptr, sf_count_t frames) ; + sf_count_t sf_readf_float (SNDFILE *sndfile, float *ptr, sf_count_t frames) ; + sf_count_t sf_readf_double (SNDFILE *sndfile, double *ptr, sf_count_t frames) ; +</PRE> +<!-- pepper --> +<P> +The file read functions fill the array pointed to by ptr with the +requested number of items or frames. +</P> + +<P> +For the frames-count functions, the frames parameter specifies the number +of frames. A frame is just a block of samples, one for each +channel. <B>Care must be taken to ensure that there is enough space +in the array pointed to by ptr, to take (frames * channels) number of +items (shorts, ints, floats or doubles). +</B></P> + +<P> +For the items-count functions, the items parameter must be an integer product +of the number of channels or an error will occur. Here, an item is just a +sample. +</P> + +<P> +Note: The only difference between the "items" and "frames" versions of +each read function is the units in which the object count is specified +- calling sf_readf_short with a count argument of N, on a SNDFILE with +C channels, is the same as calling sf_read_short with a count argument +of N*C. The buffer pointed to by "ptr" should be the same number of +bytes in each case. +</P> + +<!-- pepper --> +<P> +Note: 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 read the data using +sf_read_float(). The library seamlessly converts between the two +formats on-the-fly. See +<A HREF="#note1">Note 1</A>. +</P> +<!-- pepper --> +<P> +The sf_read_XXXX and sf_readf_XXXX functions return the number of +items or frames read, respectively. Unless the end of the file was +reached during the read, the return value should equal the number of +objects requested. Attempts to read beyond the end of the file will +not result in an error but will cause the read functions to return +less than the number of objects requested or 0 if already at the end +of the file. +</P> + +<A NAME="write"></A> +<H2><BR><B>File Write Functions</B></H2> + +<PRE> + sf_count_t sf_write_short (SNDFILE *sndfile, short *ptr, sf_count_t items) ; + sf_count_t sf_write_int (SNDFILE *sndfile, int *ptr, sf_count_t items) ; + sf_count_t sf_write_float (SNDFILE *sndfile, float *ptr, sf_count_t items) ; + sf_count_t sf_write_double (SNDFILE *sndfile, double *ptr, sf_count_t items) ; +</PRE> + +<A NAME="writef"></A> +<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 functions write the data in the array pointed to by ptr to the file. +</P> + +<P> +For items-count functions, the items parameter specifies the size of +the array and must be an integer product of the number of channels or +an error will occur. +</P> + +<P> +For the frames-count functions, the array is expected to be large enough +to hold a number of items equal to the product of frames and the +number of channels. +</P> + +<P>As with the read functions <A HREF="#read">above</A>, the only +difference in the items and frames version of each write function is +the units in which the buffer size is specified. Again, the data type +used by the calling program and the data format of the file do not +need to be the same (<A HREF="#note1">Note 1</A>). +</P> + +<P> +The sf_write_XXXX and sf_writef_XXXX functions respectively return the +number of items or frames written (which should be the same as the +items or 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> +<b>Note:</b> Unless you are writing an external decoder/encode that uses +libsndfile to handle the file headers, you should not be using these +functions. +</P> + +<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> + +<p> +See also : <a href="command.html#SFC_RAW_NEEDS_ENDSWAP">SFC_RAW_NEEDS_ENDSWAP</a> +</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, + SF_STR_ALBUM, + SF_STR_LICENSE, + SF_STR_TRACKNUMBER, + SF_STR_GENRE + } ; +</PRE> + +<P> +The sf_get_string() function returns the specified 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> +Strings passed to and retrieved from these two functions are assumed to be +utf-8. +However, while formats like Ogg/Vorbis and FLAC fully support utf-8, others +like WAV and AIFF officially only support ASCII. +Writing utf-8 strings to WAV and AIF files with libsndfile will work when read +back with libsndfile, but may not work with other programs. +</P> + +<P> +The suggested method of dealing with tags retrived using sf_get_string() is to +assume they are utf-8. +Similarly if you have a string in some exotic format like utf-16, it should be +encoded to utf-8 before being written using libsndfile. +</P> + +<HR> + +<A NAME="note1"></A> +<H2><BR><B>Note 1</B></H2> +<!-- pepper --> +<P> +When converting between integer PCM formats of differing size +(e.g. 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 : 1.0.27 +</P> +<!-- pepper --> +<!-- pepper --> +<!-- pepper --> +<!-- pepper --> + +</BODY> +</HTML>