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freeswitch


			
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	<TITLE>
	libsndfile : the sf_command function.
	</TITLE>
	<META NAME="Author"      CONTENT="Erik de Castro Lopo (erikd AT mega-nerd DOT com)">
	<!-- Another version at the bottom of the page.  -->
	<META NAME="Description" CONTENT="The libsndfile API.">
	<META NAME="Keywords"    CONTENT="WAV AIFF AU libsndfile sound audio dsp Linux">
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<BODY>

<H1><B>sf_command</B></H1>
<PRE>

        int    sf_command (SNDFILE *sndfile, int cmd, void *data, int datasize) ;
</PRE>
<P>
	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.
</P>
<P>
	The cmd parameter is a integer identifier which is defined in &lt;sndfile.h&gt;.
	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.
</P>
<P>
	The available commands are as follows:
</P>

<CENTER>
<TABLE BORDER="0" WIDTH="90%" CELLPADDING="4">
<TR>
	<TD><A HREF="#SFC_GET_LIB_VERSION">SFC_GET_LIB_VERSION</A></TD>
	<TD>Retrieve the version of the library.</TD>
</TR>
<TR>
	<TD><A HREF="#SFC_GET_LOG_INFO">SFC_GET_LOG_INFO</A></TD>
	<TD>Retrieve the internal per-file operation log.</TD>
</TR>
<TR>
	<TD><A HREF="#SFC_CALC_SIGNAL_MAX">SFC_CALC_SIGNAL_MAX</A></TD>
	<TD>Retrieve the measured maximum signal value.</TD>
</TR>
<TR>
	<TD><A HREF="#SFC_CALC_NORM_SIGNAL_MAX">SFC_CALC_NORM_SIGNAL_MAX</A></TD>
	<TD>Retrieve the measured normalised maximum signal value.</TD>
</TR>
<TR>
	<TD><A HREF="#SFC_CALC_MAX_ALL_CHANNELS">SFC_CALC_MAX_ALL_CHANNELS</A></TD>
	<TD>Calculate peaks for all channels.</TD>
</TR>
<TR>
	<TD><A HREF="#SFC_CALC_NORM_MAX_ALL_CHANNELS">SFC_CALC_NORM_MAX_ALL_CHANNELS</A></TD>
	<TD>Calculate normalised peaks for all channels.</TD>
</TR>

<TR>
	<TD><A HREF="#SFC_SET_NORM_FLOAT">SFC_SET_NORM_FLOAT</A></TD>
	<TD>Modify the normalisation behaviour of the floating point reading and writing functions.</TD>
</TR>
<TR>	
	<TD><A HREF="#SFC_SET_NORM_DOUBLE">SFC_SET_NORM_DOUBLE</A></TD>
	<TD>Modify the normalisation behaviour of the double precision floating point reading and writing functions.</TD>
</TR>
<TR>
	<TD><A HREF="#SFC_GET_NORM_FLOAT">SFC_GET_NORM_FLOAT</A></TD>
	<TD>Retrieve the current normalisation behaviour of the floating point reading and writing functions.</TD>
</TR>
<TR>	
	<TD><A HREF="#SFC_GET_NORM_DOUBLE">SFC_GET_NORM_DOUBLE</A></TD>
	<TD>Retrieve the current normalisation behaviour of the double precision floating point reading and writing functions.</TD>
</TR>
<TR>
	<TD><A HREF="#SFC_GET_SIMPLE_FORMAT_COUNT">SFC_GET_SIMPLE_FORMAT_COUNT</A></TD>
	<TD>Retrieve the number of simple formats supported by libsndfile.</TD>
</TR>
<TR>
	<TD><A HREF="#SFC_GET_SIMPLE_FORMAT">SFC_GET_SIMPLE_FORMAT</A></TD>
	<TD>Retrieve information about a simple format.</TD>
</TR>

<TR>
	<TD><A HREF="#SFC_GET_FORMAT_INFO">SFC_GET_FORMAT_INFO</A></TD>
	<TD>Retrieve information about a major or subtype format.</TD>
</TR>

<TR>
	<TD><A HREF="#SFC_GET_FORMAT_MAJOR_COUNT">SFC_GET_FORMAT_MAJOR_COUNT</A></TD>
	<TD>Retrieve the number of major formats.</TD>
</TR>
<TR>
	<TD><A HREF="#SFC_GET_FORMAT_MAJOR">SFC_GET_FORMAT_MAJOR</A></TD>
	<TD>Retrieve information about a major format type.</TD>
</TR>
<TR>
	<TD><A HREF="#SFC_GET_FORMAT_SUBTYPE_COUNT">SFC_GET_FORMAT_SUBTYPE_COUNT</A></TD>
	<TD>Retrieve the number of subformats.</TD>
</TR>
<TR>
	<TD><A HREF="#SFC_GET_FORMAT_SUBTYPE">SFC_GET_FORMAT_SUBTYPE</A></TD>
	<TD>Retrieve information about a subformat.</TD>
</TR>

<TR>
	<TD><A HREF="#SFC_SET_ADD_PEAK_CHUNK">SFC_SET_ADD_PEAK_CHUNK</A></TD>
	<TD>Switch the code for adding the PEAK chunk to WAV and AIFF files on or off.</TD>
</TR>

<TR>
	<TD><A HREF="#SFC_UPDATE_HEADER_NOW">SFC_UPDATE_HEADER_NOW</A></TD>
	<TD>Used when a file is open for write, this command will update the file
		header to reflect the data written so far.</TD>
</TR>
<TR>
	<TD><A HREF="#SFC_SET_UPDATE_HEADER_AUTO">SFC_SET_UPDATE_HEADER_AUTO</A></TD>
	<TD>Used when a file is open for write, this command will cause the file header
		to be updated after each write to the file.</TD>
</TR>

<TR>
	<TD><A HREF="#SFC_FILE_TRUNCATE">SFC_FILE_TRUNCATE</A></TD>
	<TD>Truncate a file open for write or for read/write.</TD>
</TR>

<TR>
	<TD><A HREF="#SFC_SET_RAW_START_OFFSET">SFC_SET_RAW_START_OFFSET</A></TD>
	<TD>Change the data start offset for files opened up as SF_FORMAT_RAW.</TD>
</TR>


<!--
<TR>
	<TD><A HREF="#add-dither">add dither</A></TD>
	<TD>Add dither to output on write.</TD>
</TR>
-->
</TABLE>	
</CENTER>

<BR><BR>

<HR>

<!-- ========================================================================= -->
<A NAME="SFC_GET_LIB_VERSION"></A>
<H2><BR><B>SFC_GET_LIB_VERSION</B></H2>
<P>
Retrieve the version of the library as a string.
</P>
<P>
Parameters:
<PRE>
        sndfile  : Not used
        cmd      : SFC_GET_LIB_VERSION
        data     : A pointer to a char buffer
        datasize : The size of the the buffer
</PRE>
<P>
Example:
</P>
<PRE>
        char  buffer [128] ;
        sf_command (NULL, SFC_GET_LIB_VERSION, buffer, sizeof (buffer)) ;
</PRE>

<DL>
<DT>Return value:</DT>
	<DD><DD>This call will return the length of the retrieved version string.
</DL>
<DL>
<DT>Notes:</DT>
<DD>
The string returned in the buffer passed to this function will not overflow
the buffer and will always be null terminated .
</DL>

<!-- ========================================================================= -->
<A NAME="SFC_GET_LOG_INFO"></A>
<H2><BR><B>SFC_GET_LOG_INFO</B></H2>
<P>
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.
</P>
<P>
Parameters:
<PRE>
        sndfile  : A valid SNDFILE* pointer
        cmd      : SFC_GET_LOG_INFO
        data     : A pointer to a char buffer
        datasize : The size of the the buffer
</PRE>
<P>
Example:
</P>
<PRE>
        char  buffer [2048] ;
        sf_command (sndfile, SFC_GET_LOG_INFO, buffer, sizeof (buffer)) ;
</PRE>

<DL>
<DT>Return value:</DT>
	<DD><DD>This call will return the length of the retrieved version string.
</DL>
<DL>
<DT>Notes:</DT>
<DD>
The string returned in the buffer passed to this function will not overflow
the buffer and will always be null terminated .
</DL>

<!-- ========================================================================= -->
<A NAME="SFC_CALC_SIGNAL_MAX"></A>
<H2><BR><B>SFC_CALC_SIGNAL_MAX</B></H2>
<P>
Retrieve the measured maximum signal value. This involves reading through
the whole file which can be slow on large files.
</P>
<P>
Parameters:
<PRE>
        sndfile  : A valid SNDFILE* pointer
        cmd      : SFC_CALC_SIGNAL_MAX
        data     : A pointer to a double
        datasize : sizeof (double)
</PRE>
<P>
Example:
</P>
<PRE>
        double   max_val ;
        sf_command (sndfile, SFC_CALC_SIGNAL_MAX, &amp;max_val, sizeof (max_val)) ;
</PRE>

<DL>
<DT>Return value:</DT>
	<DD><DD>Zero on success, non-zero otherwise.
</DL>

<!-- ========================================================================= -->
<A NAME="SFC_CALC_NORM_SIGNAL_MAX"></A>
<H2><BR><B>SFC_CALC_NORM_SIGNAL_MAX</B></H2>
<P>
Retrieve the measured normailised maximum signal value. This involves reading 
through the whole file which can be slow on large files.
</P>
<P>
Parameters:
<PRE>
        sndfile  : A valid SNDFILE* pointer
        cmd      : SFC_CALC_NORM_SIGNAL_MAX
        data     : A pointer to a double
        datasize : sizeof (double)
</PRE>
<P>
Example:
</P>
<PRE>
        double   max_val ;
        sf_command (sndfile, SFC_CALC_NORM_SIGNAL_MAX, &amp;max_val, sizeof (max_val)) ;
</PRE>

<DL>
<DT>Return value:</DT>
	<DD><DD>Zero on success, non-zero otherwise.
</DL>

<!-- ========================================================================= -->
<A NAME="SFC_CALC_MAX_ALL_CHANNELS"></A>
<H2><BR><B>SFC_CALC_MAX_ALL_CHANNELS</B></H2>
<P>
Calculate peaks for all channels. This involves reading through
the whole file which can be slow on large files.
</P>
<P>
Parameters:
<PRE>
        sndfile  : A valid SNDFILE* pointer
        cmd      : SFC_CALC_MAX_ALL_CHANNELS
        data     : A pointer to a double
        datasize : sizeof (double) * number_of_channels
</PRE>
<P>
Example:
</P>
<PRE>
        double   peaks [number_of_channels] ;
        sf_command (sndfile, SFC_CALC_MAX_ALL_CHANNELS, peaks, sizeof (peaks)) ;
</PRE>
<DL>
<DT>Return value:</DT>
	<DD>Zero if peaks have been calculated successfully and non-zero otherwise.
</DL>


<!-- ========================================================================= -->
<A NAME="SFC_CALC_NORM_MAX_ALL_CHANNELS"></A>
<H2><BR><B>SFC_CALC_NORM_MAX_ALL_CHANNELS</B></H2>
<P>
Calculate normalised peaks for all channels. This involves reading through
the whole file which can be slow on large files.
</P>
<P>
Parameters:
<PRE>
        sndfile  : A valid SNDFILE* pointer
        cmd      : SFC_CALC_NORM_MAX_ALL_CHANNELS
        data     : A pointer to a double
        datasize : sizeof (double) * number_of_channels
</PRE>
<P>
Example:
</P>
<PRE>
        double   peaks [number_of_channels] ;
        sf_command (sndfile, SFC_CALC_NORM_MAX_ALL_CHANNELS, peaks, sizeof (peaks)) ;
</PRE>
<DL>
<DT>Return value:</DT>
	<DD>Zero if peaks have been calculated successfully and non-zero otherwise.
</DL>


<!-- ========================================================================= -->
<!--
<A NAME="read-text"></A>
<H2><BR><B>Read text</B></H2>
<P>
Many sound file formats contain allow the inclusion of a text string describing the nature
of the file. If a file contains such a string, this functions will return it to the caller.
</P>
<P>
It should be noted that the way the string is added to the file is file format dependant
but that any string added with <A HREF="#write-text">write text</A> will be returned by 
<A HREF="#read-text">read text</A>.
</P>
<P>
<P>
Parameters:
</P>
<PRE>
        sndfile  : A valid SNDFILE* pointer
        cmd      : The text string "read text".
        data     : A pointer to a char buffer.
        datasize : The size of the the buffer.
</PRE>
<P>
Example:
</P>
<PRE>
	char  buffer [128] ;
        sf_command (sndfile, "read text", buffer, sizeof (buffer)) ;
</PRE>
<DL>
<DT>Return value:</DT>
<DD>If a text string is found, this call will return the length of the retrieved text 
	string.
	<DD>If no text string is found, zero will be returned and the first element in the 
	buffer will be set to the null character.
<DT>Notes:</DT>
<DD>The string returned in the buffer passed to this function will not overflow
	the buffer and will be correctly null terminated .
</DL>

<A NAME="write-text"></A>
<H2><BR><B>Write text</B></H2>
<P>
Add a text string to a file. The text string added can be retrieved when the file is
read using <A HREF="#read-text">read text</A>. 
</P>
<P>
Parameters:
</P>
<PRE>
        sndfile  : A valid SNDFILE* pointer
        cmd      : The text string "write text".
        data     : A pointer to the string to be added.
        datasize : Not used.
</PRE>
<P>
Example:
</P>
<PRE>
	char  text = "The sound of one hand clapping." ;
        sf_command (sndfile, "write text", text, strlen (text)) ;
</PRE>
<DL>
<DT>Return value: </DT>
	<DD>If the current file format allows the addition of text strings, the string will 
		be added and the length of the string will be returned. 
	<DD>If the file format does not allow the addition of text strings zero will be returned.
	<DD>If this function is called after the file is openned but before 
</DL>
-->


<!-- ========================================================================= -->
<A NAME="SFC_SET_NORM_FLOAT"></A>
<H2><BR><B>SFC_SET_NORM_FLOAT</B></H2>
<P>
This command only affects data read from or written to using the floating point functions:
</P>
<PRE>
	size_t    <A HREF="api.html#read">sf_read_float</A>    (SNDFILE *sndfile, float *ptr, size_t items) ;
	size_t    <A HREF="api.html#readf">sf_readf_float</A>   (SNDFILE *sndfile, float *ptr, size_t frames) ;

	size_t    <A HREF="api.html#write">sf_write_float</A>   (SNDFILE *sndfile, float *ptr, size_t items) ;
	size_t    <A HREF="api.html#writef">sf_writef_float</A>  (SNDFILE *sndfile, float *ptr, size_t frames) ;
</PRE>
<P>
Parameters:
</P>
<PRE>
        sndfile  : A valid SNDFILE* pointer
        cmd      : SFC_SET_NORM_FLOAT
        data     : NULL
        datasize : SF_TRUE or SF_FALSE
</PRE>
<P>
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].
</P>
<P>
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.
</P>
<P>
For both cases, setting normalisation to SF_FALSE means that no scaling will take place.
</P>
<P>
Example:
</P>
<PRE>
        sf_command (sndfile, SFC_SET_NORM_FLOAT, NULL, SF_TRUE) ;

        sf_command (sndfile, SFC_SET_NORM_FLOAT, NULL, SF_FALSE) ;
</PRE>
<DL>
<DT>Return value: </DT>
	<DD>Returns 1 on success or 0 for failure.
</DL>

<!-- ========================================================================= -->
<A NAME="SFC_SET_NORM_DOUBLE"></A>
<H2><BR><B>SFC_SET_NORM_DOUBLE</B></H2>
<P>
This command only affects data read from or written to using the double precision 
floating point functions:
</P>
<PRE>
	size_t    <A HREF="api.html#read">sf_read_double</A>    (SNDFILE *sndfile, double *ptr, size_t items) ;
	size_t    <A HREF="api.html#readf">sf_readf_double</A>   (SNDFILE *sndfile, double *ptr, size_t frames) ;

	size_t    <A HREF="api.html#write">sf_write_double</A>   (SNDFILE *sndfile, double *ptr, size_t items) ;
	size_t    <A HREF="api.html#writef">sf_writef_double</A>  (SNDFILE *sndfile, double *ptr, size_t frames) ;
</PRE>
<P>
Parameters:
</P>
<PRE>
        sndfile  : A valid SNDFILE* pointer
        cmd      : SFC_SET_NORM_DOUBLE
        data     : NULL
        datasize : SF_TRUE or SF_FALSE
</PRE>
<P>
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].
</P>
<P>
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.
</P>
<P>
For both cases, setting normalisation to SF_FALSE means that no scaling will take place.
</P>
<P>
Example:
</P>
<PRE>
        sf_command (sndfile, SFC_SET_NORM_DOUBLE, NULL, SF_TRUE) ;

        sf_command (sndfile, SFC_SET_NORM_DOUBLE, NULL, SF_FALSE) ;
</PRE>
<DL>
<DT>Return value: </DT>
	<DD>Returns 1 on success or 0 for failure.
</DL>

<!-- ========================================================================= -->
<A NAME="SFC_GET_NORM_FLOAT"></A>
<H2><BR><B>SFC_GET_NORM_FLOAT</B></H2>
<P>
Retrieve the current float normalisation mode.
</P>
<P>
Parameters:
</P>
<PRE>
        sndfile  : A valid SNDFILE* pointer
        cmd      : SFC_GET_NORM_FLOAT
        data     : NULL
        datasize : anything
</PRE>
<P>
Example:
</P>
<PRE>
        normalisation = sf_command (sndfile, SFC_GET_NORM_FLOAT, NULL, 0) ;
</PRE>
<DL>
<DT>Return value: </DT>
	<DD>Returns TRUE if normaisation is on and FALSE otherwise.
</DL>

<!-- ========================================================================= -->
<A NAME="SFC_GET_NORM_DOUBLE"></A>
<H2><BR><B>SFC_GET_NORM_DOUBLE</B></H2>
<P>
Retrieve the current float normalisation mode.
</P>
<P>
Parameters:
</P>
<PRE>
        sndfile  : A valid SNDFILE* pointer
        cmd      : SFC_GET_NORM_DOUBLE
        data     : NULL
        datasize : anything
</PRE>
<P>
Example:
</P>
<PRE>
        normalisation = sf_command (sndfile, SFC_GET_NORM_DOUBLE, NULL, 0) ;
</PRE>
<DL>
<DT>Return value: </DT>
	<DD>Returns TRUE if normalisation is on and FALSE otherwise.
</DL>

<!-- ========================================================================= -->
<A NAME="SFC_GET_SIMPLE_FORMAT_COUNT"></A>
<H2><BR><B>SFC_GET_SIMPLE_FORMAT_COUNT</B></H2>
<P>
Retrieve the number of simple formats supported by libsndfile.
</P>
<P>
Parameters:
</P>
<PRE>
        sndfile  : Not used.
        cmd      : SFC_GET_SIMPLE_FORMAT_COUNT
        data     : a pointer to an int
        datasize : sizeof (int)
</PRE>
<P>
Example:
</P>
<PRE>
        int  count ;
        sf_command (sndfile, SFC_GET_SIMPLE_FORMAT_COUNT, &amp;count, sizeof (int)) ;
</PRE>
<DL>
<DT>Return value: </DT>
	<DD>0
</DL>

<!-- ========================================================================= -->
<A NAME="SFC_GET_SIMPLE_FORMAT"></A>
<H2><BR><B>SFC_GET_SIMPLE_FORMAT</B></H2>
<P>
Retrieve information about a simple format.
</P>
<P>
Parameters:
</P>
<PRE>
        sndfile  : Not used.
        cmd      : SFC_GET_SIMPLE_FORMAT
        data     : a pointer to an  SF_FORMAT_INFO struct
        datasize : sizeof (SF_FORMAT_INFO)
</PRE>
<P>
The SF_FORMAT_INFO struct is defined in &lt;sndfile.h&gt; as:
</P>
<PRE>
        typedef struct
        {   int         format ;
            const char  *name ;
            const char  *extension ;
        } SF_FORMAT_INFO ;
</PRE>
<P>
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).
</P>
<P>
Example:
</P>
<PRE>
        SF_FORMAT_INFO	format_info ;
        int             k, count ;

        sf_command (sndfile, SFC_GET_SIMPLE_FORMAT_COUNT, &amp;count, sizeof (int)) ;

        for (k = 0 ; k < count ; k++)
        {   format_info.format = k ;
            sf_command (sndfile, SFC_GET_SIMPLE_FORMAT, &amp;format_info, sizeof (format_info)) ;
            printf ("%08x  %s %s\n", format_info.format, format_info.name, format_info.extension) ;
            } ;
</PRE>
<DL>
<DT>Return value: </DT>
	<DD>0 on success and non-zero otherwise.
	<DD>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.
	<DD>The name field will contain a char* pointer to the name of the string ie "WAV (Microsoft 16 bit PCM)".
	<DD>The extention field will contain the most commonly used file extension for that file type.
</DL>

<!-- ========================================================================= -->
<A NAME="SFC_GET_FORMAT_INFO"></A>
<H2><BR><B>SFC_GET_FORMAT_INFO</B></H2>
<P>
Retrieve information about a major or subtype format.
</P>
<P>
Parameters:
</P>
<PRE>
        sndfile  : Not used.
        cmd      : SFC_GET_FORMAT_INFO
        data     : a pointer to an SF_FORMAT_INFO struct
        datasize : sizeof (SF_FORMAT_INFO)
</PRE>
<P>
The SF_FORMAT_INFO struct is defined in &lt;sndfile.h&gt; as:
</P>
<PRE>
        typedef struct
        {   int         format ;
            const char  *name ;
            const char  *extension ;
        } SF_FORMAT_INFO ;
</PRE>
<P>
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.
</P>
<P>
Example:
</P>
<PRE>
        SF_FORMAT_INFO	format_info ;

        format_info.format = SF_FORMAT_WAV ;
        sf_command (sndfile, SFC_GET_FORMAT_INFO, &amp;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, &amp;format_info, sizeof (format_info)) ;
        printf ("%08x  %s\n", format_info.format, format_info.name) ;
</PRE>
<DL>
<DT>Return value: </DT>
	<DD>0 on success and non-zero otherwise.
</DL>
<!-- ========================================================================= -->
<A NAME="SFC_GET_FORMAT_MAJOR_COUNT"></A>
<H2><BR><B>SFC_GET_FORMAT_MAJOR_COUNT</B></H2>
<P>
Retrieve the number of major formats.
</P>
<P>
Parameters:
</P>
<PRE>
        sndfile  : Not used.
        cmd      : SFC_GET_FORMAT_MAJOR_COUNT
        data     : a pointer to an int
        datasize : sizeof (int)
</PRE>
<P>
Example:
</P>
<PRE>
        int  count ;
        sf_command (sndfile, SFC_GET_FORMAT_MAJOR_COUNT, &amp;count, sizeof (int)) ;
</PRE>
<DL>
<DT>Return value: </DT>
	<DD>0
</DL>

<!-- ========================================================================= -->
<A NAME="SFC_GET_FORMAT_MAJOR"></A>
<H2><BR><B>SFC_GET_FORMAT_MAJOR</B></H2>
<P>
Retrieve information about a major format type.
</P>
<P>
Parameters:
</P>
<PRE>
        sndfile  : Not used.
        cmd      : SFC_GET_FORMAT_MAJOR
        data     : a pointer to an  SF_FORMAT_INFO struct
        datasize : sizeof (SF_FORMAT_INFO)
</PRE>
<P>
Example:
</P>
<PRE>
        SF_FORMAT_INFO	format_info ;
        int             k, count ;

        sf_command (sndfile, SFC_GET_FORMAT_MAJOR_COUNT, &amp;count, sizeof (int)) ;

        for (k = 0 ; k < count ; k++)
        {   format_info.format = k ;
            sf_command (sndfile, SFC_GET_FORMAT_MAJOR, &amp;format_info, sizeof (format_info)) ;
            printf ("%08x  %s %s\n", format_info.format, format_info.name, format_info.extension) ;
            } ;
</PRE>
<P>
For a more comprehensive example, see the program list_formats.c in the examples/
directory of the libsndfile source code distribution.
</P>
<DL>
<DT>Return value: </DT>
	<DD>0 on success and non-zero otherwise.
	<DD>The value of the format field will one of the major format identifiers suc as SF_FORMAT_WAV
		SF_FORMAT_AIFF.
	<DD>The name field will contain a char* pointer to the name of the string ie "WAV (Microsoft)".
	<DD>The extention field will contain the most commonly used file extension for that file type.
</DL>

<!-- ========================================================================= -->
<A NAME="SFC_GET_FORMAT_SUBTYPE_COUNT"></A>
<H2><BR><B>SFC_GET_FORMAT_SUBTYPE_COUNT</B></H2>
<P>
Retrieve the number of subformats.
</P>
<P>
Parameters:
</P>
<PRE>
        sndfile  : Not used.
        cmd      : SFC_GET_FORMAT_SUBTYPE_COUNT
        data     : a pointer to an int
        datasize : sizeof (int)
</PRE>
<P>
Example:
</P>
<PRE>
        int   count ;
        sf_command (sndfile, SFC_GET_FORMAT_SUBTYPE_COUNT, &amp;count, sizeof (int)) ;
</PRE>
<DL>
<DT>Return value: </DT>
	<DD>0
</DL>

<!-- ========================================================================= -->
<A NAME="SFC_GET_FORMAT_SUBTYPE"></A>
<H2><BR><B>SFC_GET_FORMAT_SUBTYPE</B></H2>
<P>
Retrieve information about a subformat.
</P>
<P>
Parameters:
</P>
<PRE>
        sndfile  : Not used.
        cmd      : SFC_GET_FORMAT_SUBTYPE
        data     : a pointer to an SF_FORMAT_INFO struct
        datasize : sizeof (SF_FORMAT_INFO)
</PRE>
<P>
Example:
</P>
<PRE>
        SF_FORMAT_INFO	format_info ;
        int             k, count ;

        sf_command (sndfile, SFC_GET_FORMAT_SUBTYPE_COUNT, &amp;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, &amp;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) ;
            } ;
</PRE>
<P>
For a more comprehensive example, see the program list_formats.c in the examples/
directory of the libsndfile source code distribution.
</P>
<DL>
<DT>Return value: </DT>
	<DD>0 on success and non-zero otherwise.
	<DD>The value of the format field will one of the major format identifiers such as SF_FORMAT_WAV
		SF_FORMAT_AIFF.
	<DD>The name field will contain a char* pointer to the name of the string; for instance 
		"WAV (Microsoft)" or "AIFF (Apple/SGI)".
	<DD>The extention field will be a NULL pointer.
</DL>

<!-- ========================================================================= -->
<A NAME="SFC_SET_ADD_PEAK_CHUNK"></A>
<H2><BR><B>SFC_SET_ADD_PEAK_CHUNK</B></H2>
<P>
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.
</P>
<P>
Note : This call must be made before any data is written to the file.
</P>
<P>
Parameters:
<PRE>
        sndfile  : A valid SNDFILE* pointer
        cmd      : SFC_SET_ADD_PEAK_CHUNK
        data     : Not used (should be NULL)
        datasize : TRUE or FALSE.
</PRE>
<P>
Example:
</P>
<PRE>
        /* 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) ;
</PRE>
<DL>
<DT>Return value:</DT>
<DD>Returns SF_TRUE if the peak chunk will be written after this call.
<DD>Returns SF_FALSE if the peak chunk will not be written after this call.
</DL>

<!-- ========================================================================= -->
<A NAME="SFC_UPDATE_HEADER_NOW"></A>
<H2><BR><B>SFC_UPDATE_HEADER_NOW</B></H2>
<P>
The header of an audio file is normally written by libsndfile when the file is
closed using <B>sf_close()</B>.
</P>
<P>
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.
</P>
<P>
Parameters:
<PRE>
        sndfile  : A valid SNDFILE* pointer
        cmd      : SFC_UPDATE_HEADER_NOW
        data     : Not used (should be NULL)
        datasize : Not used.
</PRE>
<P>
Example:
</P>
<PRE>
        /* Update the header now. */
        sf_command (sndfile, SFC_UPDATE_HEADER_NOW, NULL, 0) ;
</PRE>
<DL>
<DT>Return value:</DT>
<DD>0
</DL>

<!-- ========================================================================= -->
<A NAME="SFC_SET_UPDATE_HEADER_AUTO"></A>
<H2><BR><B>SFC_SET_UPDATE_HEADER_AUTO</B></H2>
<P>
Similar to SFC_UPDATE_HEADER_NOW but updates the header at the end of every call
to the <B>sf_write*</B> functions.
</P>
<P>
Parameters:
<PRE>
        sndfile  : A valid SNDFILE* pointer
        cmd      : SFC_UPDATE_HEADER_NOW
        data     : Not used (should be NULL)
        datasize : SF_TRUE or SF_FALSE
</PRE>
<P>
Example:
</P>
<PRE>
        /* 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) ;
</PRE>
<DL>
<DT>Return value:</DT>
<DD>TRUE if auto update header is now on; FALSE otherwise.
</DL>

<!-- ========================================================================= -->
<A NAME="SFC_FILE_TRUNCATE"></A>
<H2><BR><B>SFC_FILE_TRUNCATE</B></H2>
<P>
Truncate a file open for write or for read/write.
</P>
<P>
Parameters:
<PRE>
        sndfile  : A valid SNDFILE* pointer
        cmd      : SFC_FILE_TRUNCATE
        data     : A pointer to an sf_count_t.
        datasize : sizeof (sf_count_t)
</PRE>

<P>
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.
</P>
<P>
Example:
</P>
<PRE>
        /* Truncate the file to a length of 20 frames. */
        sf_count_t  frames = 20 ;
        sf_command (sndfile, SFC_FILE_TRUNCATE, &amp;frames, sizeof (frames)) ;
</PRE>
<DL>
<DT>Return value:</DT>
	<DD>Zero on sucess, non-zero otherwise.
</DL>

<!-- ========================================================================= -->
<A NAME="SFC_SET_RAW_START_OFFSET"></A>
<H2><BR><B>SFC_SET_RAW_START_OFFSET</B></H2>
<P>
Change the data start offset for files opened up as SF_FORMAT_RAW.
</P>
<P>
Parameters:
<PRE>
        sndfile  : A valid SNDFILE* pointer
        cmd      : SFC_SET_RAW_START_OFFSET
        data     : A pointer to an sf_count_t.
        datasize : sizeof (sf_count_t)
</PRE>

<P>
For a file opened as format SF_FORMAT_RAW, set the data offset to the value
given by data.
</P>
<P>
Example:
</P>
<PRE>
        /* 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, &amp;offset, sizeof (offset)) ;
</PRE>
<DL>
<DT>Return value:</DT>
	<DD>Zero on sucess, non-zero otherwise.
</DL>

<!-- ========================================================================= -->

<HR>
<P>
	The libsndfile home page is here : 
		<A HREF="http://www.mega-nerd.com/libsndfile/">
			http://www.mega-nerd.com/libsndfile/</A>.
<BR>
Version : 1.0.25
</P>

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