[vlc-devel] [PATCH] Add a trivial audio gain filter

[Rémi Denis-Courmont]

Le mardi 27 mars 2012 19:09:11 Ludovic Fauvet, vous avez écrit :
> ---
>  modules/LIST                    |    1 +
>  modules/audio_filter/Modules.am |    2 +
>  modules/audio_filter/gain.c     |  135
> +++++++++++++++++++++++++++++++++++++++ po/POTFILES.in                  | 
>   1 +
>  4 files changed, 139 insertions(+)
>  create mode 100644 modules/audio_filter/gain.c
> 
> diff --git a/modules/LIST b/modules/LIST
> index 2e14e13..4f4cda9 100644
> --- a/modules/LIST
> +++ b/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
> diff --git a/modules/audio_filter/Modules.am
> b/modules/audio_filter/Modules.am index 90e7661..0c9b145 100644
> --- a/modules/audio_filter/Modules.am
> +++ b/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 \
> diff --git a/modules/audio_filter/gain.c b/modules/audio_filter/gain.c
> new file mode 100644
> index 0000000..e71055d
> --- /dev/null
> +++ b/modules/audio_filter/gain.c
> @@ -0,0 +1,135 @@
> +/*************************************************************************
> **** + * gain.c : gain control filter
> +
> **************************************************************************
> *** + * Copyright © 2012 VLC authors and VideoLAN
> + *
> + * Authors: Ludovic Fauvet <etix at 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_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;
> +};
> +
> +
> +/*************************************************************************
> **** + * 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( _("Gain") )
> +    set_description( _("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 ( p_filter->fmt_in.audio.i_format != VLC_CODEC_FL32 ||
> +        !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;

Laurent will beat me, but shhhh, you can store a float in a void pointer. 
There is no need to allocate memory.

> +
> +    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;
> +
> +    int i_samples = p_block->i_nb_samples;
> +    int i_channels = aout_FormatNbChannels( &p_filter->fmt_in.audio );
> +    float *p_out =  (float*)p_block->p_buffer;
> +
> +    for( int i = 0; i < i_samples; i++ )
> +    {
> +        for( int i_chan = 0; i_chan < i_channels; i_chan++ )
> +        {
> +            p_out[i_chan] *= p_sys->f_gain;
> +        }
> +        p_out += i_channels;
> +    }

It would be easier for the compiler to unroll a single loop.

> +
> +    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;
> +
> +    free( p_sys );
> +}
> diff --git a/po/POTFILES.in b/po/POTFILES.in
> index ba47415..3c74b16 100644
> --- a/po/POTFILES.in
> +++ b/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

In general, wrapping the existing volume plugins would avoid code duplication, 
especially if someone writes more volume plugins (for other formats or for 
assembler optimizations).

-- 
Rémi Denis-Courmont
http://www.remlab.net/
http://fi.linkedin.com/in/remidenis