roartut(7)						System Manager's Manual: RoarAuido						roartut(7)

NAME

       roartut - RoarAudio sound library developer tutorial

DESCRIPTION

       This  tutorial  descipes  some  basics with working with libroar. We will create a simple application that can play a file and one that can
       play some sines.  A lot of other examples can be found in RoarAudio's sources in the roarclients directory.

       This tutorial will cover some basics of the so called VS API.  The VS API is a abstract layer ontop of the normal API. It is designed to be
       simple  yet  powerful. The VS API is all you need for most applications. If you need more control over what you do you must use the normal.
       If you need only a little of those extra power you can mix VS API and normal API.

PLAYING A FILE

       Playing back a file is a easy task with libroar. The VS API has some special support to play back files in a very simple way. This is shown
       here.

       First of all we need to include the needed header files:
	#include <roaraudio.h>	/* libroar */

       This main header already includes all we need to use the VS API.

       Now  we can start our main(). We need to declare a object for the VS API as it is object oriented. This object is used to interact with the
       server and send all audio data to it:
	roar_vs_t * vss;
	int err; /* see later */

       Next we need to open the connection to the server. The most simple function to do this is roar_vs_new_from_file(3) if we are going to  play
       a file.	It takes the folloing arguments:

       server address
	      This is the address of the server. In general case This should be set to NULL.

       program name
	      This is the name of our program. This should be set to some name the user will recognize like "some App", "some Game". It should not
	      contain the filename of the process like "/usr/bin/someapp.bin".

       file name
	      This is the name of the file we want to play. In fact this is a URL.  VS API uses so called DSTR API to open files.  DSTR  API  sup-
	      ports  local  files  as  well  as  for  example  HTTP.  Examples	include: "somefile.ogg", "file:///data/bla.wav", "http://radiosta-
	      tion.org:8000/bla.ogg".

       error var
	      This is a pointer to a int used to store the error value in case of error.  This can be set to NULL but  should  not.  The  function
	      roar_vs_strerr(3) can be used to get a lion readable string of the error.

       Our call to roar_vs_new_from_file(3) will look like this:
	vss = roar_vs_new_from_file(NULL, "some App", "somefile.ogg", &err);
	if ( vss == NULL ) {
	 roar_vio_printf(roar_stderr, "Error: Can not connect to server: %s0, roar_vs_strerr(err));
	 return 1;
	}

       Next we need to continuously feed in the data so the server can do the playback.  Again most simple way is to use roar_vs_run(3).

	if ( roar_vs_run(vss, &err) == -1 ) {
	 roar_vio_printf(roar_stderr, "Error: can not loop: %s0, roar_vs_strerr(err));
	}

       This will block untill all of the file is played.

       After it returned must close the VS object. This should be done directly after roar_vs_run(3) returned. This is done this way:
	if ( roar_vs_close(vss, ROAR_VS_FALSE, &err) == -1 ) {
	 roar_vio_printf(roar_stderr, "Error: Can not close connection to server: %s0, roar_vs_strerr(err));
	 return 1;
	}

       After adding some standard main() construct we should have something like this:
	//vsfile.c:

	#include <roaraudio.h>

	int main (void) {
	 roar_vs_t * vss;
	 int err; /* see later */

	 vss = roar_vs_new_from_file(NULL, "some App", "somefile.ogg", &err);
	 if ( vss == NULL ) {
	  roar_vio_printf(roar_stderr, "Error: Can not connect to server: %s0, roar_vs_strerr(err));
	  return 1;
	 }

	 if ( roar_vs_run(vss, &err) == -1 ) {
	  roar_vio_printf(roar_stderr, "Error: can not loop: %s0, roar_vs_strerr(err));
	 }

	 if ( roar_vs_close(vss, ROAR_VS_FALSE, &err) == -1 ) {
	  roar_vio_printf(roar_stderr, "Error: Can not close connection to server: %s0, roar_vs_strerr(err));
	  return 1;
	 }

	 return 0;
	}

	//ll

       To compile and link we can use a command like this one:
	cc -o vsfile vsfile.c `roar-config --libs --cflags`

       The tool roar-config(1) will keep care for us about all flags needed for libroar.

PLAYING A SINE

       Now we want to write a application playing a sine for some secs.  We start the same way by including the correct header files:
	#include <math.h>	/* sin() */
	#include <roaraudio.h>	/* libroar */

       After that we need some basic varibales with data about the audio we want to play back:
	int rate     = ROAR_RATE_DEFAULT;
	int bits     = 16;
	int channels =	1; /* mono */

       Next we need to set the 'codec'. The codec is how the data is encoded.  We want PCM as signed ints in the native byte order of our machine.
	int codec    = ROAR_CODEC_DEFAULT;

       Now we need to store the frequency of our sine:
	float freq = 523.2;	       /* middle C */
	float step = M_PI*2*freq/rate; /* how much time per sample we have to encode ... */

       In addition we need some variables to store the current time and the length of time sine:
	float t      = 0; /* current time */
	float length = 5; /* 5 sec */

       Next we need the buffer to hold the data as well as a varible used to go thru the buffer on generation of data.
	int16_t out[1024];
	int i;

       last we need the VS object again as well as our error var:
	roar_vs_t * vss;
	int err;

       This  time  we  open  the connection to the server using roar_vs_new_playback(3).  It is similar to roar_vs_new_from_file(3) but takes some
       other options:

       server address
	      Same as above.

       program name
	      same as above.

       sample rate
	      The number of audio frames per sec.

       channels
	      The number of samples (one per channel) per audio frame.

       codec  The codec to be used. This is one of ROAR_CODEC_*.  In our case we use ROAR_CODEC_DEFAULT which is signed PCM in CPU native format.

       bits   The number of bits per sample.

       error var
	      same as above.

       The call looks like this:
	vss = roar_vs_new_playback(NULL, "vssin", rate, channels, codec, bits, &err);
	if ( vss == NULL ) {
	 roar_vio_printf(roar_stderr, "Error: Can not connect to server: %s0, roar_vs_strerr(err));
	 return 1;
	}

       Now we want to loop for length seconds:
	while (t < 2*M_PI*freq*length) {
	}

       In this loop we need to calculate our samples:
	 for (i = 0; i < (sizeof(out)/sizeof(*out)); i++) {
	  out[i] = 32767.f*sin(t);
	  t += step;
	 }

       The sine is multiplyed by 32767 as our amplitude range for 16 bit signed int is from -32768 to +32767.

       After we have our current data in out we want to write them to the server:
	 if ( roar_vs_write(vss, out, sizeof(out), &err) == -1 ) {
	  roar_vio_printf(roar_stderr, "Error: Can not write audio data to server: %s0, roar_vs_strerr(err));
	  break;
	 }

       NOTE: In a real application you may want to check the return value for short writes: Those are writes shorter than the requested amount	of
       data to be written. If you got any short writes you should try to rewrite the rest of your buffer later. This is not a error case.

       After  we  are  finished  with our main loop we have to close the connection to the server.  This is done by roar_vs_close(3) as we already
       done in the file playback example:
	if ( roar_vs_close(vss, ROAR_VS_FALSE, &err) == -1 ) {
	 roar_vio_printf(roar_stderr, "Error: Can not close connection to server: %s0, roar_vs_strerr(err));
	 return 1;
	}

       After adding some standard main() construct we should have something like this:
	//vssin.c:

	#include <roaraudio.h>
	#include <math.h>

	int main (void) {
	 roar_vs_t * vss;
	 int rate     = ROAR_RATE_DEFAULT;
	 int bits     = 16;
	 int channels =  1; /* mono */
	 int codec    = ROAR_CODEC_DEFAULT;
	 float freq = 523.2;		/* middle C */
	 float step = M_PI*2*freq/rate; /* how much time per sample we have to encode ... */
	 float t      = 0; /* current time */
	 float length = 5; /* 5 sec */
	 int16_t out[1024];
	 size_t i;
	 int err;

	 vss = roar_vs_new_playback(NULL, "vssin", rate, channels, codec, bits, &err);
	 if ( vss == NULL ) {
	  roar_vio_printf(roar_stderr, "Error: Can not connect to server: %s0, roar_vs_strerr(err));
	  return 1;
	 }

	 while (t < 2*M_PI*freq*length) {
	  for (i = 0; i < (sizeof(out)/sizeof(*out)); i++) {
	   out[i] = 32768.f*sin(t);
	   t += step;
	  }

	  if ( roar_vs_write(vss, out, sizeof(out), &err) == -1 ) {
	   roar_vio_printf(roar_stderr, "Error: Can not write audio data to server: %s0, roar_vs_strerr(err));
	   break;
	  }
	 }

	 if ( roar_vs_close(vss, ROAR_VS_FALSE, &err) == -1 ) {
	  roar_vio_printf(roar_stderr, "Error: Can not close connection to server: %s0, roar_vs_strerr(err));
	  return 1;
	 }

	 return 0;
	}

	//ll

       To compile and link we can use a command like this one:
	cc -o vssin vssin.c -lm `roar-config --libs --cflags`

       We need to use -lm to link the math library for sin().  The tool roar-config(1) will keep care for us about all flags needed for libroar.

       Now we should have a working binary vssin playing a sin() for 5 sec.

       Happy hacking!

SEE ALSO

       roar-config(1), roarcat(1), libroar(7).	RoarAudio(7).

RoarAudio							   November 2010							roartut(7)