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freeswitch/libs/libsndfile/doc/command.html
Michael Jerris f210c27f43 add libsndifle 1.0.17 to in tree libs 
git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@3761 d0543943-73ff-0310-b7d9-9358b9ac24b2
2006-12-20 19:08:07 +00:00

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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
<HEAD>
<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">
<LINK REL=StyleSheet HREF="libsndfile.css" TYPE="text/css" MEDIA="all">
</HEAD>
<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 beginning 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>Calculate the measured maximum signal value.</TD>
</TR>
<TR>
<TD><A HREF="#SFC_CALC_NORM_SIGNAL_MAX">SFC_CALC_NORM_SIGNAL_MAX</A></TD>
<TD>Calculate 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 the peak value for each channel.</TD>
</TR>
<TR>
<TD><A HREF="#SFC_CALC_NORM_MAX_ALL_CHANNELS">SFC_CALC_NORM_MAX_ALL_CHANNELS</A></TD>
<TD>Calculate the normalised peak for each channel.</TD>
</TR>
<TR>
<TD><A HREF="#SFC_GET_SIGNAL_MAX">SFC_GET_SIGNAL_MAX</A></TD>
<TD>Retrieve the peak value for the file (as stored in the file header).</TD>
</TR>
<TR>
<TD><A HREF="#SFC_GET_MAX_ALL_CHANNELS">SFC_GET_MAX_ALL_CHANNELS</A></TD>
<TD>Retrieve the peak value for each channel (as stored in the file header).</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_SET_SCALE_FLOAT_INT_READ">SFC_SET_SCALE_FLOAT_INT_READ</A></TD>
<TD>Set/clear the scale factor when integer (short/int) data is read from a file
containing floating point data.</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="#SFC_SET_CLIPPING">SFC_SET_CLIPPING</A></TD>
<TD>Turn on/off automatic clipping when doing floating point to integer
conversion.</TD>
</TR>
<TR>
<TD><A HREF="#SFC_GET_CLIPPING">SFC_GET_CLIPPING</A></TD>
<TD>Retreive current clipping setting.</TD>
</TR>
<TR>
<TD><A HREF="#SFC_GET_EMBED_FILE_INFO">SFC_GET_EMBED_FILE_INFO</A></TD>
<TD>Retreive information about audio files embedded inside other files.</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 normalised 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 the peak value (ie a single number) for each channel.
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 the normalised peak for each channel.
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="SFC_GET_SIGNAL_MAX"></A>
<H2><BR><B>SFC_GET_SIGNAL_MAX</B></H2>
<P>
Retrieve the peak value for the file as stored in the file header.
</P>
<P>
Parameters:
<PRE>
sndfile : A valid SNDFILE* pointer
cmd : SFC_GET_SIGNAL_MAX
data : A pointer to a double
datasize : sizeof (double)
</PRE>
<P>
Example:
</P>
<PRE>
double max_peak ;
sf_command (sndfile, SFC_GET_SIGNAL_MAX, &amp;max_peak, sizeof (max_peak)) ;
</PRE>
<DL>
<DT>Return value:</DT>
<DD>SF_TRUE if the file header contained the peak value. SF_FALSE otherwise.
</DL>
<!-- ========================================================================= -->
<A NAME="SFC_GET_MAX_ALL_CHANNELS"></A>
<H2><BR><B>SFC_GET_MAX_ALL_CHANNELS</B></H2>
<P>
Retrieve the peak value for the file as stored in the file header.
</P>
<P>
Parameters:
<PRE>
sndfile : A valid SNDFILE* pointer
cmd : SFC_GET_SIGNAL_MAX
data : A pointer to an array of doubles
datasize : sizeof (double) * number_of_channels
</PRE>
<P>
Example:
</P>
<PRE>
double peaks [number_of_channels] ;
sf_command (sndfile, SFC_GET_MAX_ALL_CHANNELS, peaks, sizeof (peaks)) ;
</PRE>
<DL>
<DT>Return value:</DT>
<DD>SF_TRUE if the file header contains per channel peak values for the file.
SF_FALSE otherwise.
</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 the previous float normalisation mode.
</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 the previous double normalisation mode.
</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 normalisation 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_SET_SCALE_FLOAT_INT_READ"></A>
<H2><BR><B>SFC_SET_SCALE_FLOAT_INT_READ</B></H2>
<P>
Set/clear the scale factor when integer (short/int) data is read from a file
containing floating point data.
</P>
<P>
Parameters:
</P>
<PRE>
sndfile : A valid SNDFILE* pointer
cmd : SFC_SET_SCALE_FLOAT_INT_READ
data : NULL
datasize : TRUE or FALSE
</PRE>
<P>
Example:
</P>
<PRE>
sf_command (sndfile, SFC_SET_SCALE_FLOAT_INT_READ, NULL, SF_TRUE) ;
</PRE>
<DL>
<DT>Return value: </DT>
<DD>Returns the previous SFC_SET_SCALE_FLOAT_INT_READ setting for this file.
</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 &lt;= format &lt;= 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 &lt; 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 a 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, eg. "WAV (Microsoft 16 bit PCM)".
<DD>The extension 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 &amp; SF_FORMAT_TYPEMASK) is a valid format then the struct
is filled in with information about the given major type.
If (format &amp; SF_FORMAT_TYPEMASK) is FALSE and (format &amp; 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 &lt; 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 be one of the major format identifiers such as
SF_FORMAT_WAV or SF_FORMAT_AIFF.
<DD>The name field will contain a char* pointer to the name of the string, eg. "WAV (Microsoft)".
<DD>The extension 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>
Enumerate the subtypes (this function does not translate a sub type into
a string describing that subtype).
A typical use case might be retrieving a string description of all subtypes
so that a dialog box can be filled in.
</P>
<P>
</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 1: Retrieve all subytpes supported by the WAV format.
</P>
<PRE>
SF_FORMAT_INFO format_info ;
int k, count ;
sf_command (sndfile, SFC_GET_FORMAT_SUBTYPE_COUNT, &amp;count, sizeof (int)) ;
for (k = 0 ; k &lt; 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.format | SF_FORMAT_WAV))
continue ;
printf ("%08x %s\n", format_info.format, format_info.name) ;
} ;
</PRE>
<P>
Example 2: Print a string describing the SF_FORMAT_PCM_16 subtype.
</P>
<PRE>
SF_FORMAT_INFO format_info ;
int k, count ;
sf_command (sndfile, SFC_GET_FORMAT_SUBTYPE_COUNT, &amp;count, sizeof (int)) ;
for (k = 0 ; k &lt; count ; k++)
{ format_info.format = k ;
sf_command (sndfile, SFC_GET_FORMAT_SUBTYPE, &amp;format_info, sizeof (format_info)) ;
if (format_info.format == SF_FORMAT_PCM_16)
{ printf ("%08x %s\n", format_info.format, format_info.name) ;
break ;
} ;
} ;
</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 be one of the major format identifiers such as
SF_FORMAT_WAV or 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 extension 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 that was opened for write or 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>
<!-- ========================================================================= -->
<A NAME="SFC_SET_CLIPPING"></A>
<H2><BR><B>SFC_SET_CLIPPING</B></H2>
<P>
Turn on/off automatic clipping when doing floating point to integer conversion.
</P>
<P>
Parameters:
<PRE>
sndfile : A valid SNDFILE* pointer
cmd : SFC_SET_CLIPPING
data : NULL
datasize : SF_TRUE or SF_FALSE.
</PRE>
<P>
Turn on (datasize == SF_TRUE) or off (datasize == SF_FALSE) clipping.
</P>
<P>
Example:
</P>
<PRE>
sf_command (sndfile, SFC_SET_CLIPPING, NULL, SF_TRUE) ;
</PRE>
<DL>
<DT>Return value:</DT>
<DD>Clipping mode (SF_TRUE or SF_FALSE).
</DL>
<!-- ========================================================================= -->
<A NAME="SFC_GET_CLIPPING"></A>
<H2><BR><B>SFC_GET_CLIPPING</B></H2>
<P>
Turn on/off automatic clipping when doing floating point to integer conversion.
</P>
<P>
Parameters:
<PRE>
sndfile : A valid SNDFILE* pointer
cmd : SFC_GET_CLIPPING
data : NULL
datasize : 0
</PRE>
<P>
Retrieve the current cliiping setting.
</P>
<P>
Example:
</P>
<PRE>
sf_command (sndfile, SFC_GET_CLIPPING, NULL, 0) ;
</PRE>
<DL>
<DT>Return value:</DT>
<DD>Clipping mode (SF_TRUE or SF_FALSE).
</DL>
<!-- ========================================================================= -->
<A NAME="SFC_GET_EMBED_FILE_INFO"></A>
<H2><BR><B>SFC_GET_EMBED_FILE_INFO</B></H2>
<P>
Get the file offset and file length of a file enbedded within another
larger file.
</P>
<P>
Parameters:
<PRE>
sndfile : A valid SNDFILE* pointer
cmd : SFC_GET_CLIPPING
data : a pointer to an SF_EMBED_FILE_INFO struct
datasize : sizeof (SF_EMBED_FILE_INFO)
</PRE>
<P>
The SF_FORMAT_INFO struct is defined in &lt;sndfile.h&gt; as:
</P>
<PRE>
typedef struct
{ sf_count_t offset ;
sf_count_t length ;
} SF_EMBED_FILE_INFO ;
</PRE>
<DL>
<DT>Return value: </DT>
<DD>0 on success and non-zero otherwise.
<DD>The value of the offset field of the SF_EMBED_FILE_INFO struct will be
the offsets in bytes from the start of the outer file to the start of
the audio file.
<DD>The value of the offset field of the SF_EMBED_FILE_INFO struct will be
the length in bytes of the embedded file.
</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 : 1.0.17
</P>
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