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| The libsndfile API |
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| <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"> |
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| <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 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_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_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 (Items)</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> |
| |
| <P> |
| The file read items functions fill the array pointed to by ptr with the requested |
| number of items. 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 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 functions return the number of items read. |
| Unless the end of the file was reached during the read, the return value should |
| equal the number of items requested. |
| Attempts to read beyond the end of the file will not result in an error but will |
| cause the sf_read_XXXX functions to return less than the number of items requested |
| or 0 if already at the end of the file. |
| </P> |
| |
| <A NAME="readf"></A> |
| <H2><BR><B>File Read Functions (Frames)</B></H2> |
| |
| <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 frames functions fill the array pointed to by ptr with the requested |
| number of frames of data. The array must be large enough to hold the product of |
| frames and the number of channels. |
| </P> |
| |
| <P><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> |
| The sf_readf_XXXX functions return the number of frames read. |
| Unless the end of the file was reached during the read, the return value should equal |
| the number of frames requested. |
| Attempts to read beyond the end of the file will not result in an error but will cause |
| the sf_readf_XXXX functions to return less than the number of frames requested or 0 if |
| already at the end of the file. |
| </P> |
| |
| <A NAME="write"></A> |
| <H2><BR><B>File Write Functions (Items)</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> |
| |
| <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> |
| <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> |
| <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> |
| |
| </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 : 1.0.25 |
| </P> |
| <!-- pepper --> |
| <!-- pepper --> |
| <!-- pepper --> |
| <!-- pepper --> |
| |
| </BODY> |
| </HTML> |