src/downsample.c

   1 /* libSoX effect: Downsample
   2  *
   3  * First version of this effect written 11/2011 by Ulrich Klauer.
   4  *
   5  * Copyright 2011 Chris Bagwell and SoX Contributors
   6  *
   7  * This library is free software; you can redistribute it and/or modify it
   8  * under the terms of the GNU Lesser General Public License as published by
   9  * the Free Software Foundation; either version 2.1 of the License, or (at
  10  * your option) any later version.
  11  *
  12  * This library is distributed in the hope that it will be useful, but
  13  * WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser
  15  * General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU Lesser General Public License
  18  * along with this library; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
  20  */
  21
  22 #include "sox_i.h"
  23
  24 typedef struct {
  25   unsigned int factor;
  26   unsigned int carry; /* number of samples still to be discarded,
  27                          carried over from last block */
  28 } priv_t;
  29
  30 static int create(sox_effect_t *effp, int argc, char **argv)
  31 {
  32   priv_t *p = (priv_t*)effp->priv;
  33   p->factor = 2;
  34   --argc, ++argv;
  35   do { /* break-able block */
  36     NUMERIC_PARAMETER(factor, 1, 16384)
  37   } while (0);
  38   return argc ? lsx_usage(effp) : SOX_SUCCESS;
  39 }
  40
  41 static int start(sox_effect_t *effp)
  42 {
  43   priv_t *p = (priv_t*) effp->priv;
  44   effp->out_signal.rate = effp->in_signal.rate / p->factor;
  45   return p->factor == 1 ? SOX_EFF_NULL : SOX_SUCCESS;
  46 }
  47
  48 static int flow(sox_effect_t *effp, const sox_sample_t *ibuf,
  49     sox_sample_t *obuf, size_t *isamp, size_t *osamp)
  50 {
  51   priv_t *p = (priv_t*)effp->priv;
  52   size_t ilen = *isamp, olen = *osamp;
  53   size_t t;
  54
  55   t = min(p->carry, ilen);
  56   p->carry -= t;
  57   ibuf += t; ilen -= t;
  58
  59   /* NB: either p->carry (usually) or ilen is now zero; hence, a
  60      non-zero value of ilen implies p->carry == 0, and there is no
  61      need to test for this in the following while and if. */
  62
  63   while (ilen >= p->factor && olen) {
  64     *obuf++ = *ibuf;
  65     ibuf += p->factor;
  66     olen--; ilen -= p->factor;
  67   }
  68
  69   if (ilen && olen) {
  70     *obuf++ = *ibuf;
  71     p->carry = p->factor - ilen;
  72     olen--; ilen = 0;
  73   }
  74
  75   *isamp -= ilen, *osamp -= olen;
  76   return SOX_SUCCESS;
  77 }
  78
  79 sox_effect_handler_t const *lsx_downsample_effect_fn(void)
  80 {
  81   static sox_effect_handler_t handler = {"downsample", "[factor (2)]",
  82     SOX_EFF_RATE | SOX_EFF_MODIFY,
  83     create, start, flow, NULL, NULL, NULL, sizeof(priv_t)};
  84   return &handler;
  85 }