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/*
(C) Alex Beregszaszi
License: GPL
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.
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.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_s* af, int cmd, void* arg)
{
af_center_t* s = af->setup;
switch(cmd){
case AF_CONTROL_REINIT:{
// Sanity check
if(!arg) return AF_ERROR;
af->data->rate = ((af_data_t*)arg)->rate;
af->data->nch = max(s->ch+1,((af_data_t*)arg)->nch);
af->data->format = AF_FORMAT_FLOAT_NE;
af->data->bps = 4;
return af_test_output(af,(af_data_t*)arg);
}
case AF_CONTROL_COMMAND_LINE:{
int ch=1;
sscanf(arg,"%i", &ch);
return control(af,AF_CONTROL_CENTER_CH | AF_CONTROL_SET, &ch);
}
case AF_CONTROL_CENTER_CH | AF_CONTROL_SET: // Requires reinit
// Sanity check
if((*(int*)arg >= AF_NCH) || (*(int*)arg < 0)){
af_msg(AF_MSG_ERROR,"[sub] Center channel number must be between "
" 0 and %i current value is %i\n", AF_NCH-1, *(int*)arg);
return AF_ERROR;
}
s->ch = *(int*)arg;
return AF_OK;
case AF_CONTROL_CENTER_CH | AF_CONTROL_GET:
*(int*)arg = s->ch;
return AF_OK;
}
return AF_UNKNOWN;
}
// Deallocate memory
static void uninit(struct af_instance_s* af)
{
if(af->data)
free(af->data);
if(af->setup)
free(af->setup);
}
// Filter data through filter
static af_data_t* play(struct af_instance_s* af, af_data_t* data)
{
af_data_t* c = data; // Current working data
af_center_t* s = af->setup; // Setup for this instance
float* a = c->audio; // Audio data
int len = c->len/4; // Number of samples in current audio block
int nch = c->nch; // Number of channels
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 c;
}
// Allocate memory and set function pointers
static int af_open(af_instance_t* af){
af_center_t* s;
af->control=control;
af->uninit=uninit;
af->play=play;
af->mul.n=1;
af->mul.d=1;
af->data=calloc(1,sizeof(af_data_t));
af->setup=s=calloc(1,sizeof(af_center_t));
if(af->data == NULL || af->setup == NULL)
return AF_ERROR;
// Set default values
s->ch = 1; // Channel nr 2
return AF_OK;
}
// Description of this filter
af_info_t af_info_center = {
"Audio filter for adding a center channel",
"center",
"Alex Beregszaszi",
"",
AF_FLAGS_NOT_REENTRANT,
af_open
};
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