Provided by: libroar-dev_0.4-2_amd64 bug

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 supports local  files  as  well  as  for
              example    HTTP.    Examples   include:   "somefile.ogg",   "file:///data/bla.wav",
              "http://radiostation.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).