sf_command
int    sf_command (SNDFILE *sndfile, int cmd, void *data, int datasize) ;
This function allows the caller to retrieve information from or change aspects of the
library behaviour.
Examples include retrieving a string containing the library version or changing the
scaling applied to floating point sample data during read and write.
Most of these operations are performed on a per-file basis.
The cmd parameter is a integer identifier which is defined in <sndfile.h>.
All of the valid command identifiers have names begining with "SFC_".
Data is passed to and returned from the library by use of a void pointer.
The library will not read or write more than datasize bytes from the void pointer.
For some calls no data is required in which case data should be NULL and datasize
may be used for some other purpose.
The available commands are as follows:
#SFC_GET_LIB_VERSION
SFC_GET_LIB_VERSION
Retrieve the version of the library.
#SFC_GET_LOG_INFO
SFC_GET_LOG_INFO
Retrieve the internal per-file operation log.
#SFC_CALC_SIGNAL_MAX
SFC_CALC_SIGNAL_MAX
Retrieve the measured maximum signal value.
#SFC_CALC_NORM_SIGNAL_MAX
SFC_CALC_NORM_SIGNAL_MAX
Retrieve the measured normalised maximum signal value.
#SFC_CALC_MAX_ALL_CHANNELS
SFC_CALC_MAX_ALL_CHANNELS
Calculate peaks for all channels.
#SFC_CALC_NORM_MAX_ALL_CHANNELS
SFC_CALC_NORM_MAX_ALL_CHANNELS
Calculate normalised peaks for all channels.
#SFC_SET_NORM_FLOAT
SFC_SET_NORM_FLOAT
Modify the normalisation behaviour of the floating point reading and writing functions.
#SFC_SET_NORM_DOUBLE
SFC_SET_NORM_DOUBLE
Modify the normalisation behaviour of the double precision floating point reading and writing functions.
#SFC_GET_NORM_FLOAT
SFC_GET_NORM_FLOAT
Retrieve the current normalisation behaviour of the floating point reading and writing functions.
#SFC_GET_NORM_DOUBLE
SFC_GET_NORM_DOUBLE
Retrieve the current normalisation behaviour of the double precision floating point reading and writing functions.
#SFC_GET_SIMPLE_FORMAT_COUNT
SFC_GET_SIMPLE_FORMAT_COUNT
Retrieve the number of simple formats supported by libsndfile.
#SFC_GET_SIMPLE_FORMAT
SFC_GET_SIMPLE_FORMAT
Retrieve information about a simple format.
#SFC_GET_FORMAT_INFO
SFC_GET_FORMAT_INFO
Retrieve information about a major or subtype format.
#SFC_GET_FORMAT_MAJOR_COUNT
SFC_GET_FORMAT_MAJOR_COUNT
Retrieve the number of major formats.
#SFC_GET_FORMAT_MAJOR
SFC_GET_FORMAT_MAJOR
Retrieve information about a major format type.
#SFC_GET_FORMAT_SUBTYPE_COUNT
SFC_GET_FORMAT_SUBTYPE_COUNT
Retrieve the number of subformats.
#SFC_GET_FORMAT_SUBTYPE
SFC_GET_FORMAT_SUBTYPE
Retrieve information about a subformat.
#SFC_SET_ADD_PEAK_CHUNK
SFC_SET_ADD_PEAK_CHUNK
Switch the code for adding the PEAK chunk to WAV and AIFF files on or off.
#SFC_UPDATE_HEADER_NOW
SFC_UPDATE_HEADER_NOW
Used when a file is open for write, this command will update the file
header to reflect the data written so far.
#SFC_SET_UPDATE_HEADER_AUTO
SFC_SET_UPDATE_HEADER_AUTO
Used when a file is open for write, this command will cause the file header
to be updated after each write to the file.
#SFC_FILE_TRUNCATE
SFC_FILE_TRUNCATE
Truncate a file open for write or for read/write.
#SFC_SET_RAW_START_OFFSET
SFC_SET_RAW_START_OFFSET
Change the data start offset for files opened up as SF_FORMAT_RAW.
SFC_GET_LIB_VERSION
Retrieve the version of the library as a string.
Parameters:
sndfile  : Not used
cmd      : SFC_GET_LIB_VERSION
data     : A pointer to a char buffer
datasize : The size of the the buffer
Example:
char  buffer [128] ;
sf_command (NULL, SFC_GET_LIB_VERSION, buffer, sizeof (buffer)) ;
Return value:
This call will return the length of the retrieved version string.
Notes:
The string returned in the buffer passed to this function will not overflow
the buffer and will always be null terminated .
SFC_GET_LOG_INFO
Retrieve the log buffer generated when opening a file as a string. This log
buffer can often contain a good reason for why libsndfile failed to open a
particular file.
Parameters:
sndfile  : A valid SNDFILE* pointer
cmd      : SFC_GET_LOG_INFO
data     : A pointer to a char buffer
datasize : The size of the the buffer
Example:
char  buffer [2048] ;
sf_command (sndfile, SFC_GET_LOG_INFO, buffer, sizeof (buffer)) ;
Return value:
This call will return the length of the retrieved version string.
Notes:
The string returned in the buffer passed to this function will not overflow
the buffer and will always be null terminated .
SFC_CALC_SIGNAL_MAX
Retrieve the measured maximum signal value. This involves reading through
the whole file which can be slow on large files.
Parameters:
sndfile  : A valid SNDFILE* pointer
cmd      : SFC_CALC_SIGNAL_MAX
data     : A pointer to a double
datasize : sizeof (double)
Example:
double   max_val ;
sf_command (sndfile, SFC_CALC_SIGNAL_MAX, &max_val, sizeof (max_val)) ;
Return value:
Zero on success, non-zero otherwise.
SFC_CALC_NORM_SIGNAL_MAX
Retrieve the measured normailised maximum signal value. This involves reading
through the whole file which can be slow on large files.
Parameters:
sndfile  : A valid SNDFILE* pointer
cmd      : SFC_CALC_NORM_SIGNAL_MAX
data     : A pointer to a double
datasize : sizeof (double)
Example:
double   max_val ;
sf_command (sndfile, SFC_CALC_NORM_SIGNAL_MAX, &max_val, sizeof (max_val)) ;
Return value:
Zero on success, non-zero otherwise.
SFC_CALC_MAX_ALL_CHANNELS
Calculate peaks for all channels. This involves reading through
the whole file which can be slow on large files.
Parameters:
sndfile  : A valid SNDFILE* pointer
cmd      : SFC_CALC_MAX_ALL_CHANNELS
data     : A pointer to a double
datasize : sizeof (double) * number_of_channels
Example:
double   peaks [number_of_channels] ;
sf_command (sndfile, SFC_CALC_MAX_ALL_CHANNELS, peaks, sizeof (peaks)) ;
Return value:
Zero if peaks have been calculated successfully and non-zero otherwise.
SFC_CALC_NORM_MAX_ALL_CHANNELS
Calculate normalised peaks for all channels. This involves reading through
the whole file which can be slow on large files.
Parameters:
sndfile  : A valid SNDFILE* pointer
cmd      : SFC_CALC_NORM_MAX_ALL_CHANNELS
data     : A pointer to a double
datasize : sizeof (double) * number_of_channels
Example:
double   peaks [number_of_channels] ;
sf_command (sndfile, SFC_CALC_NORM_MAX_ALL_CHANNELS, peaks, sizeof (peaks)) ;
Return value:
Zero if peaks have been calculated successfully and non-zero otherwise.
SFC_SET_NORM_FLOAT
This command only affects data read from or written to using the floating point functions:
size_t
api.html#read
sf_read_float
(SNDFILE *sndfile, float *ptr, size_t items) ;
size_t
api.html#readf
sf_readf_float
(SNDFILE *sndfile, float *ptr, size_t frames) ;
size_t
api.html#write
sf_write_float
(SNDFILE *sndfile, float *ptr, size_t items) ;
size_t
api.html#writef
sf_writef_float
(SNDFILE *sndfile, float *ptr, size_t frames) ;
Parameters:
sndfile  : A valid SNDFILE* pointer
cmd      : SFC_SET_NORM_FLOAT
data     : NULL
datasize : SF_TRUE or SF_FALSE
For read operations setting normalisation to SF_TRUE means that the data from all
subsequent reads will be be normalised to the range [-1.0, 1.0].
For write operations, setting normalisation to SF_TRUE means than all data supplied
to the float write functions should be in the range [-1.0, 1.0] and will be scaled
for the file format as necessary.
For both cases, setting normalisation to SF_FALSE means that no scaling will take place.
Example:
sf_command (sndfile, SFC_SET_NORM_FLOAT, NULL, SF_TRUE) ;
sf_command (sndfile, SFC_SET_NORM_FLOAT, NULL, SF_FALSE) ;
Return value:
Returns 1 on success or 0 for failure.
SFC_SET_NORM_DOUBLE
This command only affects data read from or written to using the double precision
floating point functions:
size_t
api.html#read
sf_read_double
(SNDFILE *sndfile, double *ptr, size_t items) ;
size_t
api.html#readf
sf_readf_double
(SNDFILE *sndfile, double *ptr, size_t frames) ;
size_t
api.html#write
sf_write_double
(SNDFILE *sndfile, double *ptr, size_t items) ;
size_t
api.html#writef
sf_writef_double
(SNDFILE *sndfile, double *ptr, size_t frames) ;
Parameters:
sndfile  : A valid SNDFILE* pointer
cmd      : SFC_SET_NORM_DOUBLE
data     : NULL
datasize : SF_TRUE or SF_FALSE
For read operations setting normalisation to SF_TRUE means that the data
from all subsequent reads will be be normalised to the range [-1.0, 1.0].
For write operations, setting normalisation to SF_TRUE means than all data supplied
to the double write functions should be in the range [-1.0, 1.0] and will be scaled
for the file format as necessary.
For both cases, setting normalisation to SF_FALSE means that no scaling will take place.
Example:
sf_command (sndfile, SFC_SET_NORM_DOUBLE, NULL, SF_TRUE) ;
sf_command (sndfile, SFC_SET_NORM_DOUBLE, NULL, SF_FALSE) ;
Return value:
Returns 1 on success or 0 for failure.
SFC_GET_NORM_FLOAT
Retrieve the current float normalisation mode.
Parameters:
sndfile  : A valid SNDFILE* pointer
cmd      : SFC_GET_NORM_FLOAT
data     : NULL
datasize : anything
Example:
normalisation = sf_command (sndfile, SFC_GET_NORM_FLOAT, NULL, 0) ;
Return value:
Returns TRUE if normaisation is on and FALSE otherwise.
SFC_GET_NORM_DOUBLE
Retrieve the current float normalisation mode.
Parameters:
sndfile  : A valid SNDFILE* pointer
cmd      : SFC_GET_NORM_DOUBLE
data     : NULL
datasize : anything
Example:
normalisation = sf_command (sndfile, SFC_GET_NORM_DOUBLE, NULL, 0) ;
Return value:
Returns TRUE if normalisation is on and FALSE otherwise.
SFC_GET_SIMPLE_FORMAT_COUNT
Retrieve the number of simple formats supported by libsndfile.
Parameters:
sndfile  : Not used.
cmd      : SFC_GET_SIMPLE_FORMAT_COUNT
data     : a pointer to an int
datasize : sizeof (int)
Example:
int  count ;
sf_command (sndfile, SFC_GET_SIMPLE_FORMAT_COUNT, &count, sizeof (int)) ;
Return value:
0
SFC_GET_SIMPLE_FORMAT
Retrieve information about a simple format.
Parameters:
sndfile  : Not used.
cmd      : SFC_GET_SIMPLE_FORMAT
data     : a pointer to an  SF_FORMAT_INFO struct
datasize : sizeof (SF_FORMAT_INFO)
The SF_FORMAT_INFO struct is defined in <sndfile.h> as:
typedef struct
{   int         format ;
const char  *name ;
const char  *extension ;
} SF_FORMAT_INFO ;
When sf_command() is called with SF_GET_SIMPLE_FORMAT, the value of the format
field should be the format number (ie 0
Example:
SF_FORMAT_INFO	format_info ;
int             k, count ;
sf_command (sndfile, SFC_GET_SIMPLE_FORMAT_COUNT, &count, sizeof (int)) ;
for (k = 0 ; k
Return value:
0 on success and non-zero otherwise.
The value of the format field of the SF_FORMAT_INFO struct will be an value which
can be placed in the format field of an SF_INFO struct when a file is to be opened
for write.
The name field will contain a char* pointer to the name of the string ie "WAV (Microsoft 16 bit PCM)".
The extention field will contain the most commonly used file extension for that file type.
SFC_GET_FORMAT_INFO
Retrieve information about a major or subtype format.
Parameters:
sndfile  : Not used.
cmd      : SFC_GET_FORMAT_INFO
data     : a pointer to an SF_FORMAT_INFO struct
datasize : sizeof (SF_FORMAT_INFO)
The SF_FORMAT_INFO struct is defined in <sndfile.h> as:
typedef struct
{   int         format ;
const char  *name ;
const char  *extension ;
} SF_FORMAT_INFO ;
When sf_command() is called with SF_GET_FORMAT_INFO, the format field is
examined and if (format & SF_FORMAT_TYPEMASK) is a valid format then the struct
is filled in with information about the given major type.
If (format & SF_FORMAT_TYPEMASK) is FALSE and (format & SF_FORMAT_SUBMASK) is a
valid subtype format then the struct is filled in with information about the given
subtype.
Example:
SF_FORMAT_INFO	format_info ;
format_info.format = SF_FORMAT_WAV ;
sf_command (sndfile, SFC_GET_FORMAT_INFO, &format_info, sizeof (format_info)) ;
printf ("%08x  %s %s\n", format_info.format, format_info.name, format_info.extension) ;
format_info.format = SF_FORMAT_ULAW ;
sf_command (sndfile, SFC_GET_FORMAT_INFO, &format_info, sizeof (format_info)) ;
printf ("%08x  %s\n", format_info.format, format_info.name) ;
Return value:
0 on success and non-zero otherwise.
SFC_GET_FORMAT_MAJOR_COUNT
Retrieve the number of major formats.
Parameters:
sndfile  : Not used.
cmd      : SFC_GET_FORMAT_MAJOR_COUNT
data     : a pointer to an int
datasize : sizeof (int)
Example:
int  count ;
sf_command (sndfile, SFC_GET_FORMAT_MAJOR_COUNT, &count, sizeof (int)) ;
Return value:
0
SFC_GET_FORMAT_MAJOR
Retrieve information about a major format type.
Parameters:
sndfile  : Not used.
cmd      : SFC_GET_FORMAT_MAJOR
data     : a pointer to an  SF_FORMAT_INFO struct
datasize : sizeof (SF_FORMAT_INFO)
Example:
SF_FORMAT_INFO	format_info ;
int             k, count ;
sf_command (sndfile, SFC_GET_FORMAT_MAJOR_COUNT, &count, sizeof (int)) ;
for (k = 0 ; k
For a more comprehensive example, see the program list_formats.c in the examples/
directory of the libsndfile source code distribution.
Return value:
0 on success and non-zero otherwise.
The value of the format field will one of the major format identifiers suc as SF_FORMAT_WAV
SF_FORMAT_AIFF.
The name field will contain a char* pointer to the name of the string ie "WAV (Microsoft)".
The extention field will contain the most commonly used file extension for that file type.
SFC_GET_FORMAT_SUBTYPE_COUNT
Retrieve the number of subformats.
Parameters:
sndfile  : Not used.
cmd      : SFC_GET_FORMAT_SUBTYPE_COUNT
data     : a pointer to an int
datasize : sizeof (int)
Example:
int   count ;
sf_command (sndfile, SFC_GET_FORMAT_SUBTYPE_COUNT, &count, sizeof (int)) ;
Return value:
0
SFC_GET_FORMAT_SUBTYPE
Retrieve information about a subformat.
Parameters:
sndfile  : Not used.
cmd      : SFC_GET_FORMAT_SUBTYPE
data     : a pointer to an SF_FORMAT_INFO struct
datasize : sizeof (SF_FORMAT_INFO)
Example:
SF_FORMAT_INFO	format_info ;
int             k, count ;
sf_command (sndfile, SFC_GET_FORMAT_SUBTYPE_COUNT, &count, sizeof (int)) ;
/* Retrieve all the subtypes supported by the WAV format. */
for (k = 0 ; k
For a more comprehensive example, see the program list_formats.c in the examples/
directory of the libsndfile source code distribution.
Return value:
0 on success and non-zero otherwise.
The value of the format field will one of the major format identifiers such as SF_FORMAT_WAV
SF_FORMAT_AIFF.
The name field will contain a char* pointer to the name of the string; for instance
"WAV (Microsoft)" or "AIFF (Apple/SGI)".
The extention field will be a NULL pointer.
SFC_SET_ADD_PEAK_CHUNK
By default, WAV and AIFF files which contain floating point data (subtype SF_FORMAT_FLOAT
or SF_FORMAT_DOUBLE) have a PEAK chunk.
By using this command, the addition of a PEAK chunk can be turned on or off.
Note : This call must be made before any data is written to the file.
Parameters:
sndfile  : A valid SNDFILE* pointer
cmd      : SFC_SET_ADD_PEAK_CHUNK
data     : Not used (should be NULL)
datasize : TRUE or FALSE.
Example:
/* Turn on the PEAK chunk. */
sf_command (sndfile, SFC_SET_ADD_PEAK_CHUNK, NULL, SF_TRUE) ;
/* Turn off the PEAK chunk. */
sf_command (sndfile, SFC_SET_ADD_PEAK_CHUNK, NULL, SF_FALSE) ;
Return value:
Returns SF_TRUE if the peak chunk will be written after this call.
Returns SF_FALSE if the peak chunk will not be written after this call.
SFC_UPDATE_HEADER_NOW
The header of an audio file is normally written by libsndfile when the file is
closed using
sf_close()
.
There are however situations where large files are being generated and it would
be nice to have valid data in the header before the file is complete.
Using this command will update the file header to reflect the amount of data written
to the file so far.
Other programs opening the file for read (before any more data is written) will
then read a valid sound file header.
Parameters:
sndfile  : A valid SNDFILE* pointer
cmd      : SFC_UPDATE_HEADER_NOW
data     : Not used (should be NULL)
datasize : Not used.
Example:
/* Update the header now. */
sf_command (sndfile, SFC_UPDATE_HEADER_NOW, NULL, 0) ;
Return value:
0
SFC_SET_UPDATE_HEADER_AUTO
Similar to SFC_UPDATE_HEADER_NOW but updates the header at the end of every call
to the
sf_write*
functions.
Parameters:
sndfile  : A valid SNDFILE* pointer
cmd      : SFC_UPDATE_HEADER_NOW
data     : Not used (should be NULL)
datasize : SF_TRUE or SF_FALSE
Example:
/* Turn on auto header update. */
sf_command (sndfile, SFC_SET_UPDATE_HEADER_AUTO, NULL, SF_TRUE) ;
/* Turn off auto header update. */
sf_command (sndfile, SFC_SET_UPDATE_HEADER_AUTO, NULL, SF_FALSE) ;
Return value:
TRUE if auto update header is now on; FALSE otherwise.
SFC_FILE_TRUNCATE
Truncate a file open for write or for read/write.
Parameters:
sndfile  : A valid SNDFILE* pointer
cmd      : SFC_FILE_TRUNCATE
data     : A pointer to an sf_count_t.
datasize : sizeof (sf_count_t)
Truncate the file to the number of frames specified by the sf_count_t pointed
to by data.
After this command, both the read and the write pointer will be
at the new end of the file.
This command will fail (returning non-zero) if the requested truncate position
is beyond the end of the file.
Example:
/* Truncate the file to a length of 20 frames. */
sf_count_t  frames = 20 ;
sf_command (sndfile, SFC_FILE_TRUNCATE, &frames, sizeof (frames)) ;
Return value:
Zero on sucess, non-zero otherwise.
SFC_SET_RAW_START_OFFSET
Change the data start offset for files opened up as SF_FORMAT_RAW.
Parameters:
sndfile  : A valid SNDFILE* pointer
cmd      : SFC_SET_RAW_START_OFFSET
data     : A pointer to an sf_count_t.
datasize : sizeof (sf_count_t)
For a file opened as format SF_FORMAT_RAW, set the data offset to the value
given by data.
Example:
/* Reset the data offset to 5 bytes from the start of the file. */
sf_count_t  offset = 5 ;
sf_command (sndfile, SFC_SET_RAW_START_OFFSET, &offset, sizeof (offset)) ;
Return value:
Zero on sucess, non-zero otherwise.
The libsndfile home page is here :
http://www.mega-nerd.com/libsndfile/
http://www.mega-nerd.com/libsndfile/
.
Version : 1.0.11
