libaf/af_center.c

   1 /*
   2     (C) Alex Beregszaszi
   3     License: GPL
   4
   5     This filter adds a center channel to the audio stream by
   6     averaging the left and right channel.
   7     There are two runtime controls one for setting which channel to
   8     insert the center-audio into called AF_CONTROL_SUB_CH.
   9
  10     FIXME: implement a high-pass filter for better results.
  11 */
  12
  13 #include <stdio.h>
  14 #include <stdlib.h>
  15 #include <string.h>
  16
  17 #include "af.h"
  18
  19 // Data for specific instances of this filter
  20 typedef struct af_center_s
  21 {
  22   int ch;               // Channel number which to insert the filtered data
  23 }af_center_t;
  24
  25 // Initialization and runtime control
  26 static int control(struct af_instance_s* af, int cmd, void* arg)
  27 {
  28   af_center_t* s   = af->setup;
  29
  30   switch(cmd){
  31   case AF_CONTROL_REINIT:{
  32     // Sanity check
  33     if(!arg) return AF_ERROR;
  34
  35     af->data->rate   = ((af_data_t*)arg)->rate;
  36     af->data->nch    = max(s->ch+1,((af_data_t*)arg)->nch);
  37     af->data->format = AF_FORMAT_FLOAT_NE;
  38     af->data->bps    = 4;
  39
  40     return af_test_output(af,(af_data_t*)arg);
  41   }
  42   case AF_CONTROL_COMMAND_LINE:{
  43     int   ch=1;
  44     sscanf(arg,"%i", &ch);
  45     return control(af,AF_CONTROL_CENTER_CH | AF_CONTROL_SET, &ch);
  46   }
  47   case AF_CONTROL_CENTER_CH | AF_CONTROL_SET: // Requires reinit
  48     // Sanity check
  49     if((*(int*)arg >= AF_NCH) || (*(int*)arg < 0)){
  50       af_msg(AF_MSG_ERROR,"[sub] Center channel number must be between "
  51              " 0 and %i current value is %i\n", AF_NCH-1, *(int*)arg);
  52       return AF_ERROR;
  53     }
  54     s->ch = *(int*)arg;
  55     return AF_OK;
  56   case AF_CONTROL_CENTER_CH | AF_CONTROL_GET:
  57     *(int*)arg = s->ch;
  58     return AF_OK;
  59   }
  60   return AF_UNKNOWN;
  61 }
  62
  63 // Deallocate memory
  64 static void uninit(struct af_instance_s* af)
  65 {
  66   if(af->data)
  67     free(af->data);
  68   if(af->setup)
  69     free(af->setup);
  70 }
  71
  72 // Filter data through filter
  73 static af_data_t* play(struct af_instance_s* af, af_data_t* data)
  74 {
  75   af_data_t*    c   = data;      // Current working data
  76   af_center_t*  s   = af->setup; // Setup for this instance
  77   float*        a   = c->audio;  // Audio data
  78   int           len = c->len/4;  // Number of samples in current audio block
  79   int           nch = c->nch;    // Number of channels
  80   int           ch  = s->ch;     // Channel in which to insert the center audio
  81   register int  i;
  82
  83   // Run filter
  84   for(i=0;i<len;i+=nch){
  85     // Average left and right
  86     a[i+ch] = (a[i]/2) + (a[i+1]/2);
  87   }
  88
  89   return c;
  90 }
  91
  92 // Allocate memory and set function pointers
  93 static int open(af_instance_t* af){
  94   af_center_t* s;
  95   af->control=control;
  96   af->uninit=uninit;
  97   af->play=play;
  98   af->mul.n=1;
  99   af->mul.d=1;
 100   af->data=calloc(1,sizeof(af_data_t));
 101   af->setup=s=calloc(1,sizeof(af_center_t));
 102   if(af->data == NULL || af->setup == NULL)
 103     return AF_ERROR;
 104   // Set default values
 105   s->ch = 1;     // Channel nr 2
 106   return AF_OK;
 107 }
 108
 109 // Description of this filter
 110 af_info_t af_info_center = {
 111     "Audio filter for adding a center channel",
 112     "center",
 113     "Alex Beregszaszi",
 114     "",
 115     AF_FLAGS_NOT_REENTRANT,
 116     open
 117 };