src/example2.c

   1 /* Simple example of using SoX libraries
   2  *
   3  * Copyright (c) 2008 robs@users.sourceforge.net
   4  *
   5  * This program is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License as published by the
   7  * Free Software Foundation; either version 2 of the License, or (at your
   8  * option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful, but
  11  * WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General
  13  * Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  18  */
  19
  20 #ifdef NDEBUG /* N.B. assert used with active statements so enable always. */
  21 #undef NDEBUG /* Must undef above assert.h or other that might include it. */
  22 #endif
  23
  24 #include "sox.h"
  25 #include "util.h"
  26 #include <stdio.h>
  27 #include <math.h>
  28 #include <assert.h>
  29
  30 /*
  31  * Reads input file and displays a few seconds of wave-form, starting from
  32  * a given time through the audio.   E.g. example2 song2.au 30.75 1
  33  */
  34 int main(int argc, char * argv[])
  35 {
  36   sox_format_t * in;
  37   sox_sample_t * buf;
  38   size_t blocks, block_size;
  39   /* Period of audio over which we will measure its volume in order to
  40    * display the wave-form: */
  41   static const double block_period = 0.025; /* seconds */
  42   double start_secs = 0, period = 2;
  43   char dummy;
  44   uint64_t seek;
  45
  46   /* All libSoX applications must start by initialising the SoX library */
  47   assert(sox_init() == SOX_SUCCESS);
  48
  49   assert(argc > 1);
  50   ++argv, --argc; /* Move to 1st parameter */
  51
  52   /* Open the input file (with default parameters) */
  53   assert(in = sox_open_read(*argv, NULL, NULL, NULL));
  54   ++argv, --argc; /* Move past this parameter */
  55
  56   if (argc) { /* If given, read the start time: */
  57     assert(sscanf(*argv, "%lf%c", &start_secs, &dummy) == 1);
  58     ++argv, --argc; /* Move past this parameter */
  59   }
  60
  61   if (argc) { /* If given, read the period of time to display: */
  62     assert(sscanf(*argv, "%lf%c", &period, &dummy) == 1);
  63     ++argv, --argc; /* Move past this parameter */
  64   }
  65
  66   /* Calculate the start position in number of samples: */
  67   seek = start_secs * in->signal.rate * in->signal.channels + .5;
  68   /* Make sure that this is at a `wide sample' boundary: */
  69   seek -= seek % in->signal.channels;
  70   /* Move the file pointer to the desired starting position */
  71   assert(sox_seek(in, seek, SOX_SEEK_SET) == SOX_SUCCESS);
  72
  73   /* Convert block size (in seconds) to a number of samples: */
  74   block_size = block_period * in->signal.rate * in->signal.channels + .5;
  75   /* Make sure that this is at a `wide sample' boundary: */
  76   block_size -= block_size % in->signal.channels;
  77   /* Allocate a block of memory to store the block of audio samples: */
  78   assert(buf = malloc(sizeof(sox_sample_t) * block_size));
  79
  80   /* This example program requires that the audio has precisely 2 channels: */
  81   assert(in->signal.channels == 2);
  82
  83   /* Read and process blocks of audio for the selected period or until EOF: */
  84   for (blocks = 0; sox_read(in, buf, block_size) == block_size && blocks * block_period < period; ++blocks) {
  85     double left = 0, right = 0;
  86     size_t i;
  87     static const char line[] = "===================================";
  88     int l, r;
  89
  90     for (i = 0; i < block_size; ++i) {
  91       SOX_SAMPLE_LOCALS;
  92       /* convert the sample from SoX's internal format to a `double' for
  93        * processing in this application: */
  94       double sample = SOX_SAMPLE_TO_FLOAT_64BIT(buf[i],);
  95
  96       /* The samples for each channel are interleaved; in this example
  97        * we allow only stereo audio, so the left channel audio can be found in
  98        * even-numbered samples, and the right channel audio in odd-numbered
  99        * samples: */
 100       if (i & 1)
 101         right = max(right, fabs(sample)); /* Find the peak volume in the block */
 102       else
 103         left = max(left, fabs(sample)); /* Find the peak volume in the block */
 104     }
 105
 106     /* Build up the wave form by displaying the left & right channel
 107      * volume as a line length: */
 108     l = (1 - left) * 35 + .5;
 109     r = (1 - right) * 35 + .5;
 110     printf("%8.3f%36s|%s\n", start_secs + blocks * block_period, line + l, line + r);
 111   }
 112
 113   /* All done; tidy up: */
 114   free(buf);
 115   sox_close(in);
 116   sox_quit();
 117   return 0;
 118 }