- - 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 | -Retrieve the version of the library. | -
| SFC_GET_LOG_INFO | -Retrieve the internal per-file operation log. | -
| SFC_CALC_SIGNAL_MAX | -Retrieve the measured maximum signal value. | -
| SFC_CALC_NORM_SIGNAL_MAX | -Retrieve the measured normalised maximum signal value. | -
| SFC_CALC_MAX_ALL_CHANNELS | -Calculate peaks for all channels. | -
| SFC_CALC_NORM_MAX_ALL_CHANNELS | -Calculate normalised peaks for all channels. | -
| SFC_SET_NORM_FLOAT | -Modify the normalisation behaviour of the floating point reading and writing functions. | -
| SFC_SET_NORM_DOUBLE | -Modify the normalisation behaviour of the double precision floating point reading and writing functions. | -
| SFC_GET_NORM_FLOAT | -Retrieve the current normalisation behaviour of the floating point reading and writing functions. | -
| SFC_GET_NORM_DOUBLE | -Retrieve the current normalisation behaviour of the double precision floating point reading and writing functions. | -
| SFC_GET_SIMPLE_FORMAT_COUNT | -Retrieve the number of simple formats supported by libsndfile. | -
| SFC_GET_SIMPLE_FORMAT | -Retrieve information about a simple format. | -
| SFC_GET_FORMAT_INFO | -Retrieve information about a major or subtype format. | -
| SFC_GET_FORMAT_MAJOR_COUNT | -Retrieve the number of major formats. | -
| SFC_GET_FORMAT_MAJOR | -Retrieve information about a major format type. | -
| SFC_GET_FORMAT_SUBTYPE_COUNT | -Retrieve the number of subformats. | -
| SFC_GET_FORMAT_SUBTYPE | -Retrieve information about a subformat. | -
| 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 | -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 | -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 | -Truncate a file open for write or for read/write. | -
| SFC_SET_RAW_START_OFFSET | -Change the data start offset for files opened up as SF_FORMAT_RAW. | -
-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)) ; -- -
-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)) ; -- -
-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)) ; -- -
-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)) ; -- -
-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)) ; --
-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)) ; --
-This command only affects data read from or written to using the floating point functions: -
-- size_t sf_read_float (SNDFILE *sndfile, float *ptr, size_t items) ; - size_t sf_readf_float (SNDFILE *sndfile, float *ptr, size_t frames) ; - - size_t sf_write_float (SNDFILE *sndfile, float *ptr, size_t items) ; - size_t 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) ; --
-This command only affects data read from or written to using the double precision -floating point functions: -
-- size_t sf_read_double (SNDFILE *sndfile, double *ptr, size_t items) ; - size_t sf_readf_double (SNDFILE *sndfile, double *ptr, size_t frames) ; - - size_t sf_write_double (SNDFILE *sndfile, double *ptr, size_t items) ; - size_t 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) ; --
-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) ; --
-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) ; --
-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)) ; --
-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 <= format <= count value obtained using -SF_GET_SIMPLE_FORMAT_COUNT). -
--Example: -
-
- SF_FORMAT_INFO format_info ;
- int k, count ;
-
- sf_command (sndfile, SFC_GET_SIMPLE_FORMAT_COUNT, &count, sizeof (int)) ;
-
- for (k = 0 ; k < count ; k++)
- { format_info.format = k ;
- sf_command (sndfile, SFC_GET_SIMPLE_FORMAT, &format_info, sizeof (format_info)) ;
- printf ("%08x %s %s\n", format_info.format, format_info.name, format_info.extension) ;
- } ;
-
--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) ;
-
--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)) ; --
-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 < count ; k++)
- { format_info.format = k ;
- sf_command (sndfile, SFC_GET_FORMAT_MAJOR, &format_info, sizeof (format_info)) ;
- printf ("%08x %s %s\n", format_info.format, format_info.name, format_info.extension) ;
- } ;
-
--For a more comprehensive example, see the program list_formats.c in the examples/ -directory of the libsndfile source code distribution. -
--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)) ; --
-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 < count ; k++)
- { format_info.format = k ;
- sf_command (sndfile, SFC_GET_FORMAT_SUBTYPE, &format_info, sizeof (format_info)) ;
- if (! sf_format_check (format.info | SF_FORMAT_WAV))
- continue ;
- printf ("%08x %s\n", format_info.format, format_info.name) ;
- } ;
-
--For a more comprehensive example, see the program list_formats.c in the examples/ -directory of the libsndfile source code distribution. -
--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) ; --
-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) ; --
-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) ; --
-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)) ; --
-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)) ; --
- The libsndfile home page is here :
-
- http://www.mega-nerd.com/libsndfile/.
-
-Version : 1.0.25
-