Add a trivial audio gain filter

This module is a wrapper around an audio mixer.
Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>

modules/LIST

@@ -130,6 +130,7 @@ $Id$
  * fluidsynth: Software MIDI synthetizer using libfluidsynth
  * folder: folder meta data and art finder
  * freetype: Utility to put text on video using freetype2
+ * gain: Gain audio filter
  * gaussianblur: gaussian blur video filter
  * gestures: mouse gestures control plugin
  * gl: OpenGL video output using the generic OpenGL provider

modules/audio_filter/Modules.am

@@ -2,6 +2,7 @@ SOURCES_equalizer = equalizer.c equalizer_presets.h
 SOURCES_compressor = compressor.c
 SOURCES_karaoke = karaoke.c
 SOURCES_normvol = normvol.c
+SOURCES_gain = gain.c
 SOURCES_audiobargraph_a = audiobargraph_a.c
 SOURCES_param_eq = param_eq.c
 SOURCES_scaletempo = scaletempo.c
@@ -22,6 +23,7 @@ libvlc_LTLIBRARIES += \
 	libequalizer_plugin.la \
 	libkaraoke_plugin.la \
 	libnormvol_plugin.la \
+	libgain_plugin.la \
 	libparam_eq_plugin.la \
 	libscaletempo_plugin.la \
 	libspatializer_plugin.la \

modules/audio_filter/gain.c

+/*****************************************************************************
+ * gain.c : gain control filter
+ *****************************************************************************
+ * Copyright © 2012 VLC authors and VideoLAN
+ *
+ * Authors: Ludovic Fauvet <etix@videolan.org>
+ *
+ * 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.
+ *****************************************************************************/
+
+/*****************************************************************************
+ * Preamble
+ *****************************************************************************/
+
+#ifdef HAVE_CONFIG_H
+# include "config.h"
+#endif
+
+#include <vlc_common.h>
+#include <vlc_aout.h>
+#include <vlc_aout_mixer.h>
+#include <vlc_filter.h>
+#include <vlc_plugin.h>
+
+
+/*****************************************************************************
+ * Local prototypes
+ *****************************************************************************/
+
+static int      Open        ( vlc_object_t * );
+static void     Close       ( vlc_object_t * );
+static block_t  *Process    ( filter_t *, block_t * );
+
+struct filter_sys_t
+{
+    float f_gain;
+    audio_mixer_t* p_mixer;
+};
+
+
+/*****************************************************************************
+ * Module descriptor
+ *****************************************************************************/
+
+#define GAIN_VALUE_TEXT N_( "Gain multiplier" )
+#define GAIN_VALUE_LONGTEXT N_( "Increase or decrease the gain (default 1.0)" )
+
+vlc_module_begin()
+    set_shortname( N_("Gain") )
+    set_description( N_("Gain control filter") )
+    set_category( CAT_AUDIO )
+    set_subcategory( SUBCAT_AUDIO_AFILTER )
+
+    add_float( "gain-value", 1.0, GAIN_VALUE_TEXT,
+               GAIN_VALUE_LONGTEXT, false )
+
+    set_capability( "audio filter", 0 )
+    set_callbacks( Open, Close )
+vlc_module_end()
+
+
+/*****************************************************************************
+ * Open: initialize filter
+ *****************************************************************************/
+
+static int Open( vlc_object_t *p_this )
+{
+    filter_t *p_filter = (filter_t *)p_this;
+    filter_sys_t *p_sys;
+
+    if ( !AOUT_FMTS_IDENTICAL( &p_filter->fmt_in.audio, &p_filter->fmt_out.audio ) )
+    {
+        msg_Warn( p_filter, "bad input or output format" );
+        return VLC_EGENERIC;
+    }
+
+    p_sys = p_filter->p_sys = malloc( sizeof( *p_sys ) );
+    if( !p_sys )
+        return VLC_ENOMEM;
+
+    p_sys->p_mixer = aout_MixerNew( p_this, p_filter->fmt_in.audio.i_format );
+    if( !p_sys->p_mixer )
+    {
+        msg_Warn( p_filter, "unsupported format" );
+        free( p_sys );
+        return VLC_EGENERIC;
+    }
+
+    p_sys->f_gain = var_InheritFloat( p_filter->p_parent, "gain-value" );
+    msg_Dbg( p_filter, "gain multiplier sets to %.2fx", p_sys->f_gain );
+
+    p_filter->pf_audio_filter = Process;
+    return VLC_SUCCESS;
+}
+
+
+/*****************************************************************************
+ * Process: process samples buffer
+ *****************************************************************************/
+
+static block_t *Process( filter_t *p_filter, block_t *p_block )
+{
+    filter_sys_t *p_sys = p_filter->p_sys;
+
+    aout_MixerRun( p_sys->p_mixer, p_block, p_sys->f_gain );
+
+    return p_block;
+}
+
+
+/*****************************************************************************
+ * Close: close filter
+ *****************************************************************************/
+
+static void Close( vlc_object_t *p_this )
+{
+    filter_t *p_filter = (filter_t*)p_this;
+    filter_sys_t *p_sys = p_filter->p_sys;
+
+    aout_MixerDelete( p_sys->p_mixer );
+    free( p_sys );
+}

po/POTFILES.in

@@ -308,6 +308,7 @@ 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/gain.c
 modules/audio_filter/karaoke.c
 modules/audio_filter/normvol.c
 modules/audio_filter/param_eq.c