/* (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=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 };