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/*
* This filter adds a center channel to the audio stream by
* averaging the left and right channel.
* There are two runtime controls one for setting which channel
* to insert the center-audio into called AF_CONTROL_SUB_CH.
*
* FIXME: implement a high-pass filter for better results.
*
* copyright (c) 2005 Alex Beregszaszi
*
* This file is part of MPlayer.
*
* MPlayer 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.
*
* MPlayer 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 MPlayer; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "common/common.h"
#include "af.h"
// Data for specific instances of this filter
typedef struct af_center_s
{
int ch; // Channel number which to insert the filtered data
}af_center_t;
// Initialization and runtime control
static int control(struct af_instance* af, int cmd, void* arg)
{
af_center_t* s = af->priv;
switch(cmd){
case AF_CONTROL_REINIT:{
// Sanity check
if(!arg) return AF_ERROR;
af->data->rate = ((struct mp_audio*)arg)->rate;
mp_audio_set_channels_old(af->data, MPMAX(s->ch+1,((struct mp_audio*)arg)->nch));
mp_audio_set_format(af->data, AF_FORMAT_FLOAT);
return af_test_output(af,(struct mp_audio*)arg);
}
}
return AF_UNKNOWN;
}
// Filter data through filter
static int filter(struct af_instance* af, struct mp_audio* data, int flags)
{
struct mp_audio* c = data; // Current working data
af_center_t* s = af->priv; // Setup for this instance
float* a = c->planes[0]; // Audio data
int nch = c->nch; // Number of channels
int len = c->samples*c->nch; // Number of samples in current audio block
int ch = s->ch; // Channel in which to insert the center audio
register int i;
// Run filter
for(i=0;i<len;i+=nch){
// Average left and right
a[i+ch] = (a[i]/2) + (a[i+1]/2);
}
return 0;
}
// Allocate memory and set function pointers
static int af_open(struct af_instance* af){
af->control=control;
af->filter=filter;
return AF_OK;
}
#define OPT_BASE_STRUCT af_center_t
struct af_info af_info_center = {
.info = "Audio filter for adding a center channel",
.name = "center",
.flags = AF_FLAGS_NOT_REENTRANT,
.open = af_open,
.priv_size = sizeof(af_center_t),
.options = (const struct m_option[]) {
OPT_INTRANGE("channel", ch, 0, 0, AF_NCH - 1, OPTDEF_INT(1)),
{0}
},
};
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