Add trivial ugly stereo karaoke filter

modules/LIST

@@ -167,6 +167,7 @@ $Id$
  * invert: inverse video filter
  * iomx: IPC/OpenMaxIL for Android
  * jack: jack server audio output
+ * karaoke: simple karaoke audio filter
  * kate: kate text bitstream decoder
  * libass: Subtitle renderers using libass
  * libbluray: Library to access Blu-Ray drives

modules/audio_filter/Modules.am

 SOURCES_equalizer = equalizer.c equalizer_presets.h
 SOURCES_compressor = compressor.c
+SOURCES_karaoke = karaoke.c
 SOURCES_normvol = normvol.c
 SOURCES_audiobargraph_a = audiobargraph_a.c
 SOURCES_param_eq = param_eq.c
@@ -18,6 +19,7 @@ libvlc_LTLIBRARIES += \
 	libchorus_flanger_plugin.la \
 	libcompressor_plugin.la \
 	libequalizer_plugin.la \
+	libkaraoke_plugin.la \
 	libnormvol_plugin.la \
 	libparam_eq_plugin.la \
 	libscaletempo_plugin.la \

modules/audio_filter/karaoke.c

+/*****************************************************************************
+ * karaoke.c : karaoke mode
+ *****************************************************************************
+ * Copyright © 2011 Rémi Denis-Courmont
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation; either version 2.1 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
+ *****************************************************************************/
+
+#ifdef HAVE_CONFIG_H
+# include "config.h"
+#endif
+
+#include <assert.h>
+
+#include <vlc_common.h>
+#include <vlc_aout.h>
+#include <vlc_filter.h>
+#include <vlc_plugin.h>
+
+static int Open (vlc_object_t *);
+
+vlc_module_begin ()
+    set_shortname (N_("Karaoke"))
+    set_description (N_("Simple Karaoke filter"))
+    set_category (CAT_AUDIO)
+    set_subcategory (SUBCAT_AUDIO_AFILTER)
+
+    set_capability ("audio filter", 0)
+    set_callbacks (Open, NULL)
+vlc_module_end ()
+
+static block_t *Process (filter_t *, block_t *);
+
+static int Open (vlc_object_t *obj)
+{
+    filter_t *filter = (filter_t *)obj;
+
+    if (filter->fmt_in.audio.i_format != VLC_CODEC_FL32
+     || !AOUT_FMTS_IDENTICAL(&filter->fmt_in.audio, &filter->fmt_out.audio))
+        return VLC_EGENERIC;
+
+    if (filter->fmt_in.audio.i_channels != 2)
+    {
+        msg_Err (filter, "voice removal requires stereo");
+        return VLC_EGENERIC;
+    }
+
+    filter->pf_audio_filter = Process;
+    return VLC_SUCCESS;
+}
+
+static block_t *Process (filter_t *filter, block_t *block)
+{
+    const float factor = .70710678 /* 1. / sqrtf (2) */;
+    float *spl = (float *)block->p_buffer;
+
+    for (unsigned i = block->i_nb_samples; i > 0; i--)
+    {
+        float s = (spl[0] - spl[1]) * factor;
+
+        *(spl++) = s;
+        *(spl++) = s;
+        /* TODO: set output format to mono */
+    }
+    (void) filter;
+    return block;
+}

po/POTFILES.in

@@ -300,6 +300,7 @@ modules/audio_filter/converter/format.c
 modules/audio_filter/converter/mpgatofixed32.c
 modules/audio_filter/equalizer.c
 modules/audio_filter/equalizer_presets.h
+modules/audio_filter/karaoke.c
 modules/audio_filter/normvol.c
 modules/audio_filter/param_eq.c
 modules/audio_filter/resampler/bandlimited.c