added a new resampler based on linear interpolation, giving a fair tradeoff

between sound quality and speed

configure.ac.in

@@ -553,7 +553,7 @@ PLUGINS="${PLUGINS} idct idctclassic motion mpeg_video spudec mpeg_audio"
 PLUGINS="${PLUGINS} lpcm a52"
 PLUGINS="${PLUGINS} deinterlace invert yuv wall transform distort clone crop motionblur"
 PLUGINS="${PLUGINS} float32tos16 float32tos8 float32tou16 float32tou8 a52tospdif fixed32tofloat32 fixed32tos16 s16tofloat32 s16tofloat32swab"
-PLUGINS="${PLUGINS} trivial_resampler ugly_resampler"
+PLUGINS="${PLUGINS} trivial_resampler ugly_resampler linear_resampler"
 PLUGINS="${PLUGINS} trivial_channel_mixer"
 PLUGINS="${PLUGINS} trivial_mixer spdif_mixer"
 PLUGINS="${PLUGINS} aout_file"

modules/audio_filter/resampler/Modules.am

 SOURCES_trivial_resampler = modules/audio_filter/resampler/trivial.c
 SOURCES_ugly_resampler = modules/audio_filter/resampler/ugly.c
+SOURCES_linear_resampler = modules/audio_filter/resampler/linear.c
 #SOURCES_fast = modules/audio_filter/resampler/fast.c

modules/audio_filter/resampler/linear.c

+/*****************************************************************************
+ * ugly.c : linear interpolation resampler
+ *****************************************************************************
+ * Copyright (C) 2002 VideoLAN
+ * $Id: linear.c,v 1.1 2002/11/07 21:09:59 sigmunau Exp $
+ *
+ * Authors: Sigmund Augdal <sigmunau@idi.ntnu.no>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111, USA.
+ *****************************************************************************/
+
+/*****************************************************************************
+ * Preamble
+ *****************************************************************************/
+#include <errno.h>
+#include <stdlib.h>                                      /* malloc(), free() */
+#include <string.h>
+
+#include <vlc/vlc.h>
+#include "audio_output.h"
+#include "aout_internal.h"
+
+/*****************************************************************************
+ * Local prototypes
+ *****************************************************************************/
+static int  Create    ( vlc_object_t * );
+
+static void DoWork    ( aout_instance_t *, aout_filter_t *, aout_buffer_t *,
+                        aout_buffer_t * );
+
+/*****************************************************************************
+ * Module descriptor
+ *****************************************************************************/
+vlc_module_begin();
+    set_description( _("audio filter for linear interpolation resampling") );
+    set_capability( "audio filter", 10 );
+    set_callbacks( Create, NULL );
+vlc_module_end();
+
+/*****************************************************************************
+ * Create: allocate ugly resampler
+ *****************************************************************************/
+static int Create( vlc_object_t *p_this )
+{
+    aout_filter_t * p_filter = (aout_filter_t *)p_this;
+    msg_Dbg( p_this, " trying the linear resampler");
+    if ( p_filter->input.i_rate == p_filter->output.i_rate
+          || p_filter->input.i_format != p_filter->output.i_format
+          || p_filter->input.i_channels != p_filter->output.i_channels
+          || p_filter->input.i_format != VLC_FOURCC('f','l','3','2') )
+    {
+        return VLC_EGENERIC;
+    }
+
+    p_filter->pf_do_work = DoWork;
+    p_filter->b_in_place = VLC_FALSE;
+
+    return VLC_SUCCESS;
+}
+
+/*****************************************************************************
+ * DoWork: convert a buffer
+ *****************************************************************************/
+static void DoWork( aout_instance_t * p_aout, aout_filter_t * p_filter,
+                    aout_buffer_t * p_in_buf, aout_buffer_t * p_out_buf )
+{
+    float* p_in = (float*)p_in_buf->p_buffer;
+    float* p_out = (float*)p_out_buf->p_buffer;
+
+    int i_nb_channels = aout_FormatNbChannels( &p_filter->input );
+    int i_in_nb = p_in_buf->i_nb_samples;
+    int i_out_nb = i_in_nb * p_filter->output.i_rate
+                    / p_filter->input.i_rate;
+    int i_frame_bytes = i_nb_channels * sizeof(s32);
+    int i_in, i_chan, i_out = 0;
+    double f_step = (float)i_in_nb/i_out_nb;
+    float f_pos = 1;
+    for( i_in = 0 ; i_in < i_in_nb - 1; i_in++ )
+    {
+        f_pos--;
+        while( f_pos < 1 )
+        {
+            for( i_chan = i_nb_channels ; i_chan ; )
+            {
+                i_chan--;
+                p_out[i_chan] = p_in[i_chan] +
+                    ( p_in[i_chan + i_nb_channels] - p_in[i_chan] ) * f_pos;
+                i_out++;
+            }
+            f_pos += f_step;
+            p_out += i_nb_channels;
+        }
+        p_in += i_nb_channels;
+    }
+    if ( f_step < 1 ) {
+        for( i_chan = i_nb_channels ; i_chan ; )
+        {
+            i_chan--;
+            p_out[i_chan] = p_in[i_chan];
+            i_out++;
+        }
+    }
+    if ( i_out != i_out_nb * i_nb_channels ) {
+        msg_Warn( p_aout, "mismatch in sample nubers: %d requested, %d generated", i_out_nb* i_nb_channels, i_out);
+    }
+                                              
+    p_out_buf->i_nb_samples = i_out_nb;
+    p_out_buf->i_nb_bytes = i_out_nb * i_frame_bytes;
+}
+