帧类型决策-slicetype_path_cost()

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我是靠谱客的博主干净乐曲，最近开发中收集的这篇文章主要介绍帧类型决策-slicetype_path_cost()，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

/*
计算一个路径的cost总和，若超过了阈值则立马返回
根据path中每一帧的帧类型，计算其帧cost，累加返回
总体上一段一段的计算，即以B帧开始到下一个非B帧为一段
若允许BREF，则将这一段最中间的B帧按照BREF来计算其cost
即return = SUM{ BBB...BBB(P/I), BBB...BBB(P/I), ... ,BBB...BBB(P/I) }
*/
static uint64_t slicetype_path_cost( x264_t *h, x264_mb_analysis_t *a, x264_frame_t **frames, char *path, uint64_t threshold )
{
uint64_t cost = 0;
int loc = 1;
int cur_nonb = 0;
path--; /* Since the 1st path element is really the second frame */
while( path[loc] )	//遍历paths中的每一步
{
int next_nonb = loc;
/* Find the location of the next non-B-frame. */
while( path[next_nonb] == 'B' )	//找到下一个非B帧
next_nonb++;
/* Add the cost of the non-B-frame found above 计算下一个非B帧的cost */
if( path[next_nonb] == 'P' )
cost += slicetype_frame_cost( h, a, frames, cur_nonb, next_nonb, next_nonb );
else /* I-frame */
cost += slicetype_frame_cost( h, a, frames, next_nonb, next_nonb, next_nonb );
/* Early terminate if the cost we have found is larger than the best path cost so far */
if( cost > threshold )	//若超过了阈值则尽早结束
break;
if( h->param.i_bframe_pyramid && next_nonb - cur_nonb > 2 )
{	// 将 N B B B B B N => N B B BREF B B N
//得到中值作为BREF
int middle = cur_nonb + (next_nonb - cur_nonb)/2;
//计算中间的BREF的cost
cost += slicetype_frame_cost( h, a, frames, cur_nonb, next_nonb, middle );
//累计当前B帧直到中间BFRE之间的B帧cost和, 即 N (B B B.. B) BREF
for( int next_b = loc; next_b < middle && cost < threshold; next_b++ )
cost += slicetype_frame_cost( h, a, frames, cur_nonb, middle, next_b );
//累计中间BFRE到下一非B帧之间的B帧cost和,即 BREF (B B B.. B) N
for( int next_b = middle+1; next_b < next_nonb && cost < threshold; next_b++ )
cost += slicetype_frame_cost( h, a, frames, middle, next_nonb, next_b );
}
else	//累计这一段B的cost
for( int next_b = loc; next_b < next_nonb && cost < threshold; next_b++ )
cost += slicetype_frame_cost( h, a, frames, cur_nonb, next_nonb, next_b );
loc = next_nonb + 1;
cur_nonb = next_nonb;
}
return cost;
}