mpv/libaf/af_extrastereo.c

/*=============================================================================
//	
//  This software has been released under the terms of the GNU Public
//  license. See http://www.gnu.org/copyleft/gpl.html for details.
//
//  Copyright 2004 Alex Beregszaszi & Pierre Lombard
//
//=============================================================================
*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h> 

#include <unistd.h>
#include <inttypes.h>
#include <math.h>
#include <limits.h>

#include "af.h"

// Data for specific instances of this filter
typedef struct af_extrastereo_s
{
    float mul;
}af_extrastereo_t;

// Initialization and runtime control
static int control(struct af_instance_s* af, int cmd, void* arg)
{
  af_extrastereo_t* s   = (af_extrastereo_t*)af->setup; 

  switch(cmd){
  case AF_CONTROL_REINIT:
    // Sanity check
    if(!arg) return AF_ERROR;
    
    if(((af_data_t*)arg)->format != (AF_FORMAT_SI | AF_FORMAT_NE) ||
       (((af_data_t*)arg)->nch != 2))
       return AF_ERROR;

    af->data->rate   = ((af_data_t*)arg)->rate;
    af->data->nch    = 2;
    af->data->format = AF_FORMAT_SI | AF_FORMAT_NE;
    af->data->bps    = 2;

    return af_test_output(af,(af_data_t*)arg);
  case AF_CONTROL_COMMAND_LINE:{
    float f;
    sscanf((char*)arg,"%f", &f);
    s->mul = f;
    return AF_OK;
  }
  case AF_CONTROL_ES_MUL | AF_CONTROL_SET:
    s->mul = *(float*)arg;
    return AF_OK;
  case AF_CONTROL_ES_MUL | AF_CONTROL_GET:
    *(float*)arg = s->mul;
    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_extrastereo_t *s = af->setup;
  register int i = 0;
  int16_t *a = (int16_t*)data->audio;	// Audio data
  int len = data->len/2;		// Number of samples
  int avg, l, r;
  
  for (i = 0; i < len; i+=2)
  {
    avg = (a[i] + a[i + 1]) / 2;
    
    l = avg + (int)(s->mul * (a[i] - avg));
    r = avg + (int)(s->mul * (a[i + 1] - avg));

    a[i] = clamp(l, SHRT_MIN, SHRT_MAX);
    a[i + 1] = clamp(r, SHRT_MIN, SHRT_MAX);
  }

  return data;
}

// Allocate memory and set function pointers
static int open(af_instance_t* af){
  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=calloc(1,sizeof(af_extrastereo_t));
  if(af->data == NULL || af->setup == NULL)
    return AF_ERROR;

  ((af_extrastereo_t*)af->setup)->mul = 2.5;
  return AF_OK;
}

// Description of this filter
af_info_t af_info_extrastereo = {
    "Extra stereo",
    "extrastereo",
    "Alex Beregszaszi & Pierre Lombard",
    "",
    AF_FLAGS_NOT_REENTRANT,
    open
};