x264运动估计宏块cost值的计算

一、 x264运动估计中宏块的位移cost计算:

/* lambda = pow(2,qp/6-2) */
const byte x264_lambda_tab[52] =
{
   1, 1, 1, 1, 1, 1, 1, 1,  /*  0-7 */
   1, 1, 1, 1,              /*  8-11 */
   1, 1, 1, 1, 2, 2, 2, 2,  /* 12-19 */
   3, 3, 3, 4, 4, 4, 5, 6,  /* 20-27 */
   6, 7, 8, 9,10,11,13,14,  /* 28-35 */
  16,18,20,23,25,29,32,36,  /* 36-43 */
  40,45,51,57,64,72,81,91   /* 44-51 */
};

/*根据量化参数得到i_lambda的值*/
int i_qpm = 10; /*取值0 - 51; 每个宏块的qpm都是变化的,在函数x264_ratecontrol_mb中改变qpm值*/
int i_lambda = x264_lambda_tab[i_qpm];

/*计算i_lambda时所有位移的cost值*/
short *cost_mv[92];
malloc(cost_mv[i_lambda], (4*4*2048 + 1) * sizeof(short) );
cost_mv[i_lambda] += 2*4*2048;
for( i = 0; i <= 2*4*2048; i++ )
{
    cost_mv[i_lambda][-i] = cost_mv[i_lambda][i] 
        = (short)( i_lambda * (log2f((float)( i+1 ))*2 + 0.718f + !!i) + .5f );
}

/*得到实际位移cost*/
int i_mvx = -1;
int i_mvy = 2;
int i_cost = cost_mv[i_mvx] + cost_mv[i_mvy];

二、 x264运动估计中宏块的参考帧cost计算:

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

static const byte x264_ue_size_tab[256] =
{
     1, 1, 3, 3, 5, 5, 5, 5, 7, 7, 7, 7, 7, 7, 7, 7,
     9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9,
    11,11,11,11,11,11,11,11,11,11,11,11,11,11,11,11,
    11,11,11,11,11,11,11,11,11,11,11,11,11,11,11,11,
    13,13,13,13,13,13,13,13,13,13,13,13,13,13,13,13,
    13,13,13,13,13,13,13,13,13,13,13,13,13,13,13,13,
    13,13,13,13,13,13,13,13,13,13,13,13,13,13,13,13,
    13,13,13,13,13,13,13,13,13,13,13,13,13,13,13,13,
    15,15,15,15,15,15,15,15,15,15,15,15,15,15,15,15,
    15,15,15,15,15,15,15,15,15,15,15,15,15,15,15,15,
    15,15,15,15,15,15,15,15,15,15,15,15,15,15,15,15,
    15,15,15,15,15,15,15,15,15,15,15,15,15,15,15,15,
    15,15,15,15,15,15,15,15,15,15,15,15,15,15,15,15,
    15,15,15,15,15,15,15,15,15,15,15,15,15,15,15,15,
    15,15,15,15,15,15,15,15,15,15,15,15,15,15,15,15,
    15,15,15,15,15,15,15,15,15,15,15,15,15,15,15,15,
};

static inline int bs_size_te( int x, int val )
{
    if( x == 1 )
        return 1;
    else
        return x264_ue_size_tab[val+1];
}

static inline int x264_clip3( int v, int i_min, int i_max )
{
    return ( (v < i_min) ? i_min : (v > i_max) ? i_max : v );
}

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

int i_lambda;  /*i_lambda的获取同上*/

/* 92: i_lambda值; 3: 当前编码帧的参考帧数量(大于3时设为3); 33: 参考帧序号 */
static short x264_cost_ref[92][3][33]; 

for( int i = 0; i < 3; i++ )
{
    for( int j = 0; j < 33; j++ )
    {
        x264_cost_ref[i_lambda][i][j] = i ? i_lambda * bs_size_te( i, j ) : 0;
    }
}

int i_num_ref_idx_l0_active = h->i_ref0 <= 0 ? 1 : h->i_ref0;  /* 当前编码帧的ref0参考帧数量 */              
int i_num_ref_idx_l1_active = h->i_ref1 <= 0 ? 1 : h->i_ref1;  /* 当前编码帧的ref1参考帧数量 */

short *p_cost_ref[2];  /* ref0和ref1 */
p_cost_ref[0] = x264_cost_ref[i_lambda][x264_clip3(i_num_ref_idx_l0_active-1,0,2)];
p_cost_ref[1] = x264_cost_ref[i_lambda][x264_clip3(i_num_ref_idx_l1_active-1,0,2)];

/*得到实际参考帧i_ref的cost*/
int i_cost_ref0 = p_cost_ref[0][i_ref];
int i_cost_ref1 = p_cost_ref[1][i_ref];

总结:(1)一个参考帧时, i_cost_ref始终为0;
          (2)两个参考帧时, i_cost_ref为i_lambda;
          (3)大于等于3个参考帧时, i_cost_ref要根据参考帧的序号来计算。

 

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