aac_back_pred.c

JPEG-MPEG編解碼技術書集的代碼

/*********************************************************************
 *
 * aac_back_pred.c  -  AAC 后向预测程序
 *
 *
**********************************************************************/

/**********************************************************************

INPUT:
"	act_spec[]表示当前帧要编码的频谱成分；
"	last_spec[]表示前一帧的量化频谱误差；
"	btype为当前帧的窗口类型；
"	]nsfb为比例因子频带的数目；
"	isfb_width[]为比例因子带宽。

OUTPUT:
"	act_spec[]为当前要编码帧的频谱误差；
"	pred_global_flag为全局预测使能/禁止标志；
"	pred_sbf_glag[]为每个比例因子通带的使能和禁止标志；
"	reset_group为其余组的数目，如果为-1则表示没有其余的组。

***********************************************************************/

#include "aac_back_pred.h"


static int psy_init_mc[MAX_TIME_CHANNELS];
static float dr_mc[MAX_TIME_CHANNELS][LPC][FLEN_LONG/2],e_mc[MAX_TIME_CHANNELS][LPC+1+1][FLEN_LONG/2];
static float K_mc[MAX_TIME_CHANNELS][LPC+1][FLEN_LONG/2], R_mc[MAX_TIME_CHANNELS][LPC+1][FLEN_LONG/2];
static float VAR_mc[MAX_TIME_CHANNELS][LPC+1][FLEN_LONG/2], KOR_mc[MAX_TIME_CHANNELS][LPC+1][FLEN_LONG/2];
static float sb_samples_pred_mc[MAX_TIME_CHANNELS][FLEN_LONG/2];
static int thisLineNeedsResetting_mc[MAX_TIME_CHANNELS][FLEN_LONG/2];
static int reset_count_mc[MAX_TIME_CHANNELS];

void PredInit() {
  int i;
  for (i=0;i<MAX_TIME_CHANNELS;i++) {
    psy_init_mc[i] = 0;
    reset_count_mc[i] = 0;
  }
}
 
void PredCalcPrediction( double *act_spec, double *last_spec, int btype, 
            int nsfb, int *isfb_width, short *pred_global_flag, 
            int *pred_sfb_flag, int *reset_group ,
	    int chanNum) 
{
  int i, k, j, cb_long;
  float num_bit, snr[SBMAX_L];
  float energy[FLEN_LONG/2], snr_p[FLEN_LONG/2], temp1, temp2;

  /* 为指定的信道设定指针*/
 
  int *psy_init;
  float (*dr)[FLEN_LONG/2],(*e)[FLEN_LONG/2];
  float (*K)[FLEN_LONG/2], (*R)[FLEN_LONG/2];
  float (*VAR)[FLEN_LONG/2], (*KOR)[FLEN_LONG/2];
  float *sb_samples_pred;
  int *thisLineNeedsResetting;
  /* int reset_count; */
  int *reset_count;

  /* psy_init = psy_init_mc[chanNum]; */
  psy_init = &psy_init_mc[chanNum];
  dr = &dr_mc[chanNum][0];
  e = &e_mc[chanNum][0];
  K = &K_mc[chanNum][0]; 
  R = &R_mc[chanNum][0];
  VAR = &VAR_mc[chanNum][0];
  KOR = &KOR_mc[chanNum][0];
  sb_samples_pred = &sb_samples_pred_mc[chanNum][0];
  thisLineNeedsResetting = &thisLineNeedsResetting_mc[chanNum][0];
  reset_count = &reset_count_mc[chanNum];

  *psy_init = (*psy_init && (btype!=2));

  if((*psy_init) == 0) {
    for (j=0; j<FLEN_LONG/2; j++) {
      thisLineNeedsResetting[j]=1;
    }
    *psy_init = 1;
  }

  if (btype==2) {
    pred_global_flag[0]=0;

 
    *reset_count = ((*reset_count) / RESET_FRAME) * RESET_FRAME;
    return;
  }



  /**************************************************/
    /* 计算使用last_spec 的状态 */
  /**************************************************/
  for (i=0;i<FLEN_LONG/2;i++) 
    {
      /* e[0][i]=last_spec[i]; */ 
      e[0][i]=last_spec[i]+sb_samples_pred[i];
      
      for(j=1;j<=LPC;j++)
	e[j][i] = e[j-1][i]-K[j][i]*R[j-1][i];
      
      for(j=1;j<LPC;j++) 
	dr[j][i] = K[j][i]*e[j-1][i];
      
      for(j=1;j<=LPC;j++) {
	VAR[j][i] = ALPHA*VAR[j][i]+.5*(R[j-1][i]*R[j-1][i]+e[j-1][i]*e[j-1][i]);
	KOR[j][i] = ALPHA*KOR[j][i]+R[j-1][i]*e[j-1][i];
      }

      for(j=LPC-1;j>=1;j--) 
	R[j][i] = A*(R[j-1][i]-dr[j][i]);
      R[0][i] = A*e[0][i];
    }


  /**************************************************/
  /*   在这里重置状态*/           
  /**************************************************/
   for (i=0;i<FLEN_LONG/2;i++) {
     if (thisLineNeedsResetting[i]) {
       for (j = 0; j <= LPC; j++)
	 {
	   K[j][i] = 0.0;
	   dr[j][i] = 0.0;
	   e[j][i] = 0.0;
	   R[j][i] = 0.0;
	   VAR[j][i] = 1.0;
	   KOR[j][i] = 0.0;
	 }
     }
   }



  /**************************************************/
   /* 计算预测器系数和预测数据*/
  /**************************************************/
   for (i=0;i<FLEN_LONG/2;i++) 
    {
      for(j=1;j<=LPC;j++) {
	if(VAR[j][i]>MINVAR)
	  K[j][i] = KOR[j][i]/VAR[j][i]*B;
	else
	  K[j][i] = 0;
      }
    }


   for (k=0; k<FLEN_LONG/2; k++)
    {
      sb_samples_pred[k]=0.0;
      for (i=1; i<=LPC; i++)
	sb_samples_pred[k]+=K[i][k]*R[i-1][k];
    }



  /**************************************************/
    /* 判断是否使能或禁止预测*/
  /**************************************************/

  for (k=0; k<FLEN_LONG/2; k++)
    {energy[k]=act_spec[k]*act_spec[k];
     snr_p[k]=(act_spec[k]-sb_samples_pred[k])*(act_spec[k]-sb_samples_pred[k]);
   }
  
  cb_long=0;
  for (i=0; i<nsfb; i++)
    {
      pred_sfb_flag[i]=1;
      temp1=0.0;
      temp2=0.0;
      for (j=cb_long; j<cb_long+isfb_width[i]; j++)
	{temp1+=energy[j]; temp2+=snr_p[j];}
      if(temp2<1.e-20) temp2=1.e-20;
      if(temp1!=0.0) {snr[i]=-10.*log10((double ) temp2/temp1);}
      else snr[i]=0.0;
      if(snr[i]<=0.0) {pred_sfb_flag[i]=0; 
		       for (j=cb_long; j<cb_long+isfb_width[i]; j++)
			 sb_samples_pred[j]=0.0; }
      cb_long+=isfb_width[i];
    }

  /* Disable prediction for bands nsfb through SBMAX_L */ 
  for (i=j;i<FLEN_LONG/2;i++) {
    sb_samples_pred[i]=0.0;
  }
  for (i=nsfb;i<SBMAX_L;i++) {
     pred_sfb_flag[i]=0;
  }

  num_bit=0.0;
  for (i=0; i<nsfb; i++)
    if(snr[i]>0.0) num_bit+=snr[i]/6.*isfb_width[i];	

  pred_global_flag[0]=1;
  if(num_bit<100 /*50*/) {
    pred_global_flag[0]=0; num_bit=0.0; 
    for (j=0; j<FLEN_LONG/2; j++)
      sb_samples_pred[j]=0.0; 
  }
  for (j=0; j<FLEN_LONG/2; j++)
    act_spec[j]-=sb_samples_pred[j];



 


  (*reset_count)++;
  /* Reset the frame counter */
  for (i=0;i<FLEN_LONG/2;i++) {
    thisLineNeedsResetting[i]=0;
  }
  if (*reset_count >= 31 * RESET_FRAME)
    *reset_count = RESET_FRAME;
  if (*reset_count % RESET_FRAME == 0)
  { /* Send a reset in this frame */
    *reset_group = *reset_count / 8;

    for (i = *reset_group - 1; i < FLEN_LONG / 2; i += 30)
    {
      thisLineNeedsResetting[i]=1;
    }
  }
  else
    *reset_group = -1;



 

 /* Ensure that prediction data is sent when there is a prediction
  * reset.
  */
  if (*reset_group != -1 && pred_global_flag[0] == 0)
  {
    pred_global_flag[0] = 1;
    for (i = 0; i < nsfb; i++)
      pred_sfb_flag[i] = 0;
  }
 /* End of code segment */


}