modules/audio_filter/karaoke.c

   1 /*****************************************************************************
   2  * karaoke.c : karaoke mode
   3  *****************************************************************************
   4  * Copyright © 2011 Rémi Denis-Courmont
   5  *
   6  * This program is free software; you can redistribute it and/or modify it
   7  * under the terms of the GNU Lesser General Public License as published by
   8  * the Free Software Foundation; either version 2.1 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  14  * GNU Lesser General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU Lesser General Public License
  17  * along with this program; if not, write to the Free Software Foundation,
  18  * Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
  19  *****************************************************************************/
  20
  21 #ifdef HAVE_CONFIG_H
  22 # include "config.h"
  23 #endif
  24
  25 #include <vlc_common.h>
  26 #include <vlc_aout.h>
  27 #include <vlc_filter.h>
  28 #include <vlc_plugin.h>
  29
  30 static int Open (vlc_object_t *);
  31
  32 vlc_module_begin ()
  33     set_shortname (N_("Karaoke"))
  34     set_description (N_("Simple Karaoke filter"))
  35     set_category (CAT_AUDIO)
  36     set_subcategory (SUBCAT_AUDIO_AFILTER)
  37
  38     set_capability ("audio filter", 0)
  39     set_callbacks (Open, NULL)
  40 vlc_module_end ()
  41
  42 static block_t *Process (filter_t *, block_t *);
  43
  44 static int Open (vlc_object_t *obj)
  45 {
  46     filter_t *filter = (filter_t *)obj;
  47
  48     if (filter->fmt_in.audio.i_channels != 2)
  49     {
  50         msg_Err (filter, "voice removal requires stereo");
  51         return VLC_EGENERIC;
  52     }
  53
  54     filter->fmt_in.audio.i_format = VLC_CODEC_FL32;
  55     aout_FormatPrepare(&filter->fmt_in.audio);
  56     filter->fmt_out.audio = filter->fmt_in.audio;
  57     filter->pf_audio_filter = Process;
  58     return VLC_SUCCESS;
  59 }
  60
  61 static block_t *Process (filter_t *filter, block_t *block)
  62 {
  63     const float factor = .70710678 /* 1. / sqrtf (2) */;
  64     float *spl = (float *)block->p_buffer;
  65
  66     for (unsigned i = block->i_nb_samples; i > 0; i--)
  67     {
  68         float s = (spl[0] - spl[1]) * factor;
  69
  70         *(spl++) = s;
  71         *(spl++) = s;
  72         /* TODO: set output format to mono */
  73     }
  74     (void) filter;
  75     return block;
  76 }