SoX(3)                         Sound eXchange_ng                        SoX(3)



NAME
       libsox_ng, another audio file-format and effect library

SYNOPSIS
       #include <sox_ng.h>

       int sox_format_init(void);

       void sox_format_quit(void);

       sox_format_t *sox_open_read(const char *path, const sox_signalinfo_t *info, sox_encodinginfo_t const *encoding, const char *filetype);

       sox_format_t *sox_open_write(char const *filename, sox_signalinfo_t const *info, sox_encodinginfo_t const *encoding, char const *filetype, sox_oob_t const *oob, sox_bool (*overwrite_permitted)(char const *filename));

       sox_size_t sox_read(sox_format_t *ft, sox_sample_t *buf, sox_size_t len);

       sox_size_t sox_write(sox_format_t *ft, sox_sample_t const *buf, sox_size_t len);

       int sox_close(sox_format_t Ift);

       int sox_seek(sox_format_t *ft, sox_size_t offset, int whence);

       sox_effect_handler_t const *sox_find_effect(char const *name);

       sox_effect_t *sox_create_effect(sox_effect_handler_t const *eh);

       int sox_effect_options(sox_effect_t *effp, int argc, char * const argv[]);

       sox_effects_chain_t *sox_create_effects_chain(sox_encodinginfo_t const *in_enc, sox_encodinginfo_t const *out_enc);

       int sox_add_effect(sox_effects_chaint_t *chain, sox_effect_t*effp, sox_signalinfo_t *in, sox_signalinfo_t const *out);

       void sox_delete_effects_chain(sox_effects_chain_t *ecp);

       cc file.c -o file -lsox_ng

DESCRIPTION
       libsox_ng  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.

       This is not really a manual for the libsox_ng API; it is a quick intro-
       duction to the basic operations for reading and writing audio files and
       to use effect chains, followed by notes on how to write new format han-
       dlers and effects.  For an exhaustive description of the libsox_ng  API
       see http://martinwguy.net/test/soxygen/sox_8h.html

       sox_format_init()  performs  initialization required by all file format
       handlers.  If compiled with dynamic library support, this  will  detect
       and  initialize all external libraries.  It should be called before any
       file operations are performed.

       sox_format_quit() performs some required cleanup related  to  all  file
       format handlers.

       sox_open_read()  opens  a  file  for  reading  whose name is the string
       pointed to by path and associates a sox_format_t with  it.   A  special
       name  of  "-" reads data from stdin.  If info is not NULL, it specifies
       the data format of the input file and if encoding is not NULL it  gives
       information  already  known  about the sample encoding.  These are nor-
       mally only needed for headerless audio files where that information  is
       not stored in the file.  If filetype is non-NULL, it specifies the file
       type.  If it is NULL, the file type is determined  by  looking  at  the
       file header and/or the filename extension.  Upon successful completion,
       sox_open_read() returns a handle to the new session, which should even-
       tually be closed with sox_close(), or NULL otherwise.

       [3]  TODO: Need a way to return reason for failures.  Currently, it re-
       lies on sox_warn to print information.

       sox_open_write() opens a file for writing  whose  name  is  the  string
       pointed  to  by  path and associates a sox_format_t with it.  A special
       name of "-" writes data to stdout.  info specifies the data  format  of
       the  output  file.  The info structure from an input format handler can
       be used to copy data using the same format.  If encoding is  not  NULL,
       it  specifies the desired sample encoding.  Since most file formats can
       write data in different data formats, this usually has to be specified;
       if  NULL, a default is used.  If filetype is non-NULL, it specifies the
       file type.  If it is NULL, SoX derives the file type from the  filename
       extension.  If oob is not NULL, it specifies out-of-band data to add to
       the file such as comments, instrument information and  loop  points  if
       the  file type supports them.  sox_open_write() returns a handle to the
       new session, which must be closed with sox_close(), or NULL on failure.

       sox_read() reads len samples into buf using the format handler ft.  All
       data  is converted to 32-bit signed samples before being placed in buf.
       The value of len is in total samples and if its value is not  divisable
       by  the number of channels, anything might happen.  It returns the num-
       ber of samples read or zero at the end of the file or if an  error  oc-
       curred.  sox_read's return value does not distiguish between the end of
       a file and an error but you can inspect ft->sox_errno to tell the  dif-
       ference.   It  should be SOX_SUCCESS or SOX_EOF unless some other error
       has occurred previously; you can clear ft->sox_errno to 0 beforehand to
       be sure.

       sox_read()  and  sox_write()  return the number of samples successfully
       read or written. If an error occurs or the end of the file is  reached,
       the  return  value  is  a short item count or SOX_EOF, depending on the
       function.

       sox_write() writes len samples from buf using the  format  handler  ft.
       Data  in  buf  must be 32-bit signed samples which are converted during
       the writing process.  The value of len is specified  in  total  samples
       and  must  be divisable by the number of channels, otherwise unexpected
       things will occur.  It returns the actual number  of  samples  encoded,
       zero if an error occurred.

       sox_close() dissociates a sox_format_t from its underlying file and set
       of functions.  If the format handler was used for output, any  buffered
       data  is written first.  It returns SOX_SUCCESS if everything went well
       or the return value from the format's stopread or  stopwrite  (probably
       SOX_EOF)  otherwise  and  the  precise  reason for failure is passed to
       sox_warn() or sox_fail() to print the information.  In either case,  no
       further  use  should  be  made  to the handle, not even another call to
       sox_close().

       sox_find_effect() finds the effect called name, returning a pointer  to
       its sox_effect_handler_t if it exists, NULL otherwise.

       sox_create_effect()  instantiates  an  effect into a sox_effect_t given
       the address of a sox_effect_handler_t Any missing methods are automati-
       cally  set  to the appropriate nothing method.  It returns a pointer to
       the new effect or NULL if it was not found or had problems starting up.

       sox_effect_options() passes options into an effect to control  its  be-
       havior.   If  it  succeeds, effp->in_signal may[1] contain the rate and
       channel count at which it requires input data and effp->out_signal  may
       contain  the  rate  and  channel count it outputs.  When it is present,
       this information is used[2] to  ensure  that  appropriate  effects  are
       placed  in  the effects chain to handle any needed conversions.  It re-
       turns the number of arguments consumed or SOX_EOF if  any  invalid  op-
       tions were passed.

       [1] Does the effect have the option of setting these or can you option-
       ally set them?

       [2] Does it do this automatically or do you have to add the  right  ef-
       fects?

       Setting  options  is  only supported before the effect is started.  The
       behavior is undefined  if  its  called  when  the  effect  has  already
       started.

       sox_create_effects_chain()  creates  an  effects chain to which effects
       can be added.  in_enc and  out_enc  are  the  signal  encoding  of  the
       chain's  input  and  output.   The  pointers  to in_enc and out_enc are
       stored internally, so their memory should not be freed until the effect
       chain  has  been deleted.  Their values may change to reflect new input
       or output encodings when effects start up or are restarted.  It returns
       a pointer to the new chain or NULL if something went wrong.

       sox_add_effect  adds an effect to a chain.  in specifies the input sig-
       nal info for the effect, out is a suggestion as to what the output sig-
       nal should be but, depending on the effect options given and on in, the
       effect can choose to do differently.  Whatever output rate and channels
       the  effect  produces  are written back to in.  in should be stored and
       passed to each call to sox_add_effect so that changes propagate to each
       new effect.  It returns SOX_SUCCESS if it was successful.

       sox_delete_effects_chain() closes an effects chain and releases any re-
       sources  reserved  during  the  creation  of  the  chain.    It   calls
       sox_delete_effects() if any effects are still in the chain.

       SoX  includes  skeleton  C  files  to assist you in writing new formats
       (skelform.c) and effects (skeleff.c).  New formats can often just  deal
       with the header and then use raw.c's routines for reading and writing.

       example0.c and example1.c are a good starting point to see how to write
       applications using libsox_ng and sox_ng.c itself is also a good  refer-
       ence.

RETURN VALUE
       sox_seek returns 0 if it succeeds, SOX_EOF otherwise

       [6] TODO Need to set a global error and implement sox_tell.

ERRORS
       [7] TODO

INTERNALS
       SoX's  formats  and  effects  operate with an internal sample format of
       signed 32-bit integer.  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 in-
       put  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.

       Representing samples as integers can cause problems when processing au-
       dio.  For example, if an effect to mix down  left  and  right  channels
       into one monophonic channel were to use the line
          *obuf++ = (*ibuf++ + *ibuf++)/2;
       distortion  may  occur  since the intermediate addition can overflow 32
       bits.
          *obuf++ = *ibuf++/2 + *ibuf++/2;
       would get round the overflow but at the expense of the  least  signifi-
       cant bit.

       Stereo  data  is stored with the left and right speaker data in succes-
       sive samples and quadraphonic data is stored left front,  right  front,
       left rear, right rear.

FORMATS
       A  format is responsible for translating between sound sample files and
       an internal buffer.  The internal buffer is stored in signed longs with
       a fixed sampling rate.  The format operates from two data structures: a
       format structure and a private structure.

       The format structure contains a list of control parameters for the  au-
       dio:  sampling  rate, data size (8, 16 or 32 bits), encoding (unsigned,
       signed, floating point etc.), and the number  of  sound  channels.   It
       also contains other state information: whether the sample file needs to
       be byte-swapped, whether sox_seek() will work,  its  suffix,  its  file
       stream pointer, its format pointer and the format's private structure.

       The  private  area  is  a preallocated data array for the format to use
       however it wishes.  It should have a defined data  structure  and  cast
       the  array to that structure.  See voc.c for an example of 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 nto the header.  The private area is usually not very large and some
       effects,  such  as  echo, lsx_malloc() larger areas for delay lines and
       such.

       A format has 6 routines:

       startread           Set up the format parameters, read in a data header
                           or do anything else that needs to be done.

       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.  it returns the num-
                           ber of samples actually read.

       stopread            Do what needs to be done when it has finished read-
                           ing.

       startwrite          Set  up  the  format  parameters, maybe write out a
                           data header and any  any  other  preliminaries  for
                           writing the format.

       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, it will  re-
                           turn [7].

       [7] What? SOX_EOF or a short-or-0 number of samples?

       stopwrite           Typically,  fix up the file header or whatever else
                           needs to be done.

EFFECTS
       Each effect runs with one input and one output stream.  An effect's im-
       plementation  comprises  six  functions that may be called according to
       the following flow diagram:
       LOOP (invocations with different parameters)
         getopts
         LOOP (invocations with the same parameters)
           LOOP (channels)
             start
           LOOP (while there is input audio to process)
             LOOP (channels)
               flow
           LOOP (while there is output audio to generate)
             LOOP (channels)
               drain
           LOOP (channels)
             stop
         kill
       Functions that an effect does not need can be NULL.  An effect that  is
       marked  `MCHAN' does not use the LOOP (channels) lines and must perform
       multiple channel processing inside the  affected  functions.   Multiple
       effect instances may be processed in parallel.

       getopts             is called with a character string argument list for
                           the effect.

       start               is called with the signal parameters for the  input
                           and output streams.

       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 out-
                           put buffer, and sets the size variables to the num-
                           bers 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 SOX_EOF, this means  that  the  effect
                           will  not  read  any  more  data and can be used to
                           switch to drain mode sooner.

       drain               is called when there are no more  input  data  sam-
                           ples.   If  the effect wishes to generate more data
                           samples, it copies  the  generated  data  into  the
                           given buffer and returns the number of samples gen-
                           erated.  If it fills the buffer, it will be  called
                           again; The echo effect uses this to fade away.

       stop                is  called when there are no more input samples and
                           no more output samples to process.  It is typically
                           used  to close or free resources such as memory and
                           temporary files that were allocated  during  start.
                           See echo.c for an example.

       kill                is  called  to allow resources allocated by getopts
                           to be released.  See pad.c for an example.

LINKING
       How you link against libsox_ng depends on how SoX  was  built  on  your
       system.  For  a  static build, just link against the library. For a dy-
       namic build, use libtool to link with the correct linker flags. See the
       libtool manual for details; basically, you use it like this:
          libtool --mode=link gcc -o prog /path/to/libsox_ng.la

LICENSE
       Copyright  1991-2015  Lance Norskog, Chris Bagwell and sundry contribu-
       tors.

       This library is free software; you can redistribute it and/or modify it
       under  the  terms of the GNU General Public License version 2.1 as pub-
       lished by the Free Software Foundation.

       This library is distributed in the hope that it  will  be  useful,  but
       WITHOUT  ANY  WARRANTY;  without  even  the  implied  warranty  of MER-
       CHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU  General
       Public License for more details.

AUTHORS
       The many authors and contributors are listed in the README file that is
       distributed with the source code.

SEE ALSO
       sox_ng(1), soxformat_ng(7), example*.c in the SoX source distribution.



libsox_ng                      February 19, 2011                        SoX(3)
