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.de Sh
.br
.ne 5
.PP
\fB\\$1\fR
.PP
..
.de Sp
.if t .sp .5v
.if n .sp
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.TH ST 3 "September 26 2005"
.SH NAME
libst \- Sound Tools : sound sample file and effects libraries.
.SH SYNOPSIS
.B #include <st.h>
.P
.B ft_t st_open_input(const char *\fIpath\fB, const st_signalinfo_t *\fIinfo\fB, const char *\fIfiletype\fB);
.P
.B ft_t st_open_output(const char *\fIpath\fB, const st_signalinfo_t *\fIinfo\fB, const char *\fIfiletype\fB, const char *\fIcomment\fB);
.P
.B st_ssize_t st_read(ft_t \fIft\fB, st_sample_t *\fIbuf\fB, st_ssize_t \fIlen\fB);
.P
.B st_ssize_t st_write(ft_t \fIft\fB, st_sample_t *\fIbuf\fB, st_ssize_t \fIlen\fB);
.P
.B int st_close(ft_t \fIft\fB);
.P
.B int st_seek(ft_t \fIft\fB, st_size_t \fIoffset\fB, int \fIwhence\fB);
.P
.B cc \fIfile.c\fB -o \fIfile \fBlibst.a
.SH DESCRIPTION
.I Sound\ Tools
is a library of sound sample file format readers/writers and sound
effects processors. It is mainly developed for use by SoX but is
useful for any sound application.
.P
\fBst_open_input\fR function opens the file for reading whose name is
the string pointed to by \fIpath\fR and associates an ft_t with it. If
\fIinfo\fR is non-NULL then it will be used to specify the data format
of the input file. This is normally only needed for headerless audio
files since the information is not stored in the file. If
\fIfiletype\fR is non-NULL then it will be used to specify the file
type. If this is not specified then the file type is attempted to be
derived by looking at the file header and/or the filename extension. A
special name of "-" can be used to read data from stdin.
.P
\fBst_open_output\fR function opens the file for writing whose name is
the string pointed to by \fIpath\fR and associates an ft_t with it. If
\fIinfo\fR is non-NULL then it will be used to specify the data format
of the output file. Since most file formats can write data in
different data formats, this generally has to be specified. The info
structure from the input format handler can be specified to copy data
over in the same format. If \fIcomment\fR is non-NULL, it will be
written in the file header for formats that support comments. If
\fIfiletype\fR is non-NULL then it will be used to specify the file
type. If this is not specified then the file type is attempted to be
derived by looking at the filename extension. A special name of "-"
can be used to write data to stdout.
.P
The function \fBst_read\fR reads \fIlen\fR samples in to \fIbuf\fR
using the format handler specified by \fIft\fR. All data read is
converted to 32-bit signed samples before being placed in to
\fIbuf\fR. The value of \fIlen\fR is specified in total samples. If
its value is not evenly divisable by the number of channels, undefined
behavior will occur.
.P
The function \fBst_write\fR writes \fIlen\fR samples from \fIbuf\fR
using the format handler specified by \fIft\fR. Data in \fIbuf\fR must
be 32-bit signed samples and will be converted during the write
process. The value of \fIlen\fR is specified in total samples. If its
value is not evenly divisable by the number of channels, undefined
behavior will occur.
.P
The \fBst_close\fR function dissociates the named \fIft_t\fR from its
underlying file or set of functions. If the format handler was being
used for output, any buffered data is written first.
.P
SoX includes skeleton C files to assist you in writing new
formats (skelform.c) and effects (skeleff.c). sox.c itself is a good
starting point for new programs. Note that new formats can often just
deal with the header and then use raw.c's routines for reading and
writing.
.SH RETURN VALUE
Upon successful completion \fBst_open_input\fR and
\fBst_open_output\fR return a ft_t (which is a pointer). Otherwise,
NULL is returned. TODO: Need a what to return reason for failures.
Currently, relies on st_warn to print information.
.P
\fBst_read\fR and \fBst_write\fR return the number of samples
successfully read or written. If an error occurs, or the end-of-file
is reached, the return value is a short item count or ST_EOF. TODO:
\fBst_read\fR does not distiguish between end-of-ifle and error. Need
an feof() and ferror() concept to determine which occured.
.P
Upon successful completion \fBst_close\fR returns 0. Otherwise, ST_EOF
is returned. In either case, any further access (including another
call to \fBst_close\fR()) to the handler results in undefined
behavior. TODO: Need a way to return reason for failures. Currently,
relies on st_warn to print information.
.P
Upon successful completion \fBst_seek\fR returns 0. Otherwise, ST_EOF
is returned. TODO Need to set a global error and implement st_tell.
.SH ERRORS
TODO
.SH INTERNALS
SoX's formats and effects operate on an internal buffer format of
signed 32-bit longs. The data processing routines are called with
buffers of these samples, and buffer sizes which refer to the number
of samples processed, not the number of bytes. File readers translate
the input samples to signed 32-bit integers and return the number of
samples read. For example, data in linear signed byte format is
left-shifted 24 bits.
.P
This does cause problems in processing the data.  
For example:
.br
	*obuf++ = (*ibuf++ + *ibuf++)/2;
.br
would
.I not
mix down left and right channels into one monophonic channel,
because the resulting samples would overflow 32 bits.
Instead, the ``avg'' effects must use:
.br
	*obuf++ = *ibuf++/2 + *ibuf++/2;
.br
.P
Stereo data is stored with the left and right speaker data in
successive samples.
Quadraphonic data is stored in this order: 
left front, right front, left rear, right rear.
.SH FORMATS
A 
.I format 
is responsible for translating between sound sample files
and an internal buffer.  The internal buffer is store in signed longs
with a fixed sampling rate.  The 
.I format
operates from two data structures:
a format structure, and a private structure.
.P
The format structure contains a list of control parameters for
the sample: sampling rate, data size (8, 16, or 32 bits),
encoding (unsigned, signed, floating point, etc.), number of sound channels.
It also contains other state information: whether the sample file
needs to be byte-swapped, whether st_seek() will work, its suffix,
its file stream pointer, its 
.I format
pointer, and the 
.I private
structure for the 
.I format .
.P
The 
.I private 
area is just a preallocated data array for the 
.I format
to use however it wishes.  
It should have a defined data structure
and cast the array to that structure.  
See voc.c for the use of a private data area.  
Voc.c has to track the number of samples it 
writes and when finishing, seek back to the beginning of the file
and write it out.
The private area is not very large.
The ``echo'' effect has to malloc() a much larger area for its
delay line buffers.
.P
A 
.I format
has 6 routines:
.TP 20
startread
Set up the format parameters, or read in
a data header, or do what needs to be done.
.TP 20
read
Given a buffer and a length: 
read up to that many samples, 
transform them into signed long integers,
and copy them into the buffer.
Return the number of samples actually read.
.TP 20
stopread
Do what needs to be done.
.TP 20
startwrite
Set up the format parameters, or write out 
a data header, or do what needs to be done.
.TP 20
write
Given a buffer and a length: 
copy that many samples out of the buffer,
convert them from signed longs to the appropriate
data, and write them to the file.
If it can't write out all the samples,
fail.
.TP 20
stopwrite
Fix up any file header, or do what needs to be done.
.SH EFFECTS
An effects loop has one input and one output stream.
It has 5 routines.
.TP 20
getopts
is called with a character string argument list for the effect.
.TP 20
start
is called with the signal parameters for the input and output
streams.
.TP 20 
flow
is called with input and output data buffers,
and (by reference) the input and output data buffer sizes.
It processes the input buffer into the output buffer,
and sets the size variables to the numbers of samples
actually processed.
It is under no obligation to read from the input buffer or
write to the output buffer during the same call.  If the
call returns ST_EOF then this should be used as an indication
that this effect will no longer read any data and can be used
to switch to drain mode sooner.
.TP 20 
drain
is called after there are no more input data samples.
If the effect wishes to generate more data samples
it copies the generated data into a given buffer
and returns the number of samples generated.
If it fills the buffer, it will be called again, etc.
The echo effect uses this to fade away.
.TP 20
stop
is called when there are no more input samples to process.
.I stop
may generate output samples on its own.
See echo.c for how to do this, 
and see that what it does is absolutely bogus.
.SH BUGS
The program/library interface is pretty weak.
.SH SEE ALSO
.BR soxexam (7),
.BR soxlua (7),
.BR libst (3)
.SH AUTHORS
No idea.