threads
sprintf( s, " threads=%d", p->i_threads );最大值128 X264_THREAD_MAX。
如果没有设置threads参数，x264根据当前cpu核数以及slice_threads计算应该设置的编码线程个数
h->param.i_threads = x264_cpu_num_processors() * (h->param.b_sliced_threads?2:3)/2;
从代码看:x264_threadpool_run( h->threadpool, (void*)x264_slices_write, h );
void x264_threadpool_run( x264_threadpool_t *pool, void *(*func)(void *), void *arg )
{
x264_threadpool_job_t *job = (void*)x264_sync_frame_list_pop( &pool->uninit );
job->func = func;
job->arg = arg;
x264_sync_frame_list_push( &pool->run, (void*)job );
}
void x264_sync_frame_list_push( x264_sync_frame_list_t *slist, x264_frame_t *frame )
{
x264_pthread_mutex_lock( &slist->mutex );
while( slist->i_size == slist->i_max_size )
x264_pthread_cond_wait( &slist->cv_empty, &slist->mutex );
slist->list[ slist->i_size++ ] = frame;
x264_pthread_mutex_unlock( &slist->mutex );
x264_pthread_cond_broadcast( &slist->cv_fill );
}
这里是以帧为单位的多线程编码，当线程数量过大，会导致线程之间相互参考等待，已经线程调度等问题，建议不要超过16.
sliced-threads 一帧是否分slice
默认值0，一帧一个slice
值为1表示一帧多个slice。
lookahead_threads：参考线程个数，按线程个数分块编码，块之间参考关系相互独立。
for( int i = 0; i < h->param.i_lookahead_threads; i++ )
{
x264_t *t = h->lookahead_thread[i];
/* FIXME move this somewhere else 填充编码参数*/
t->mb.i_me_method = h->mb.i_me_method;
t->mb.i_subpel_refine = h->mb.i_subpel_refine;
t->mb.b_chroma_me = h->mb.b_chroma_me;
s[i] = (x264_slicetype_slice_t){ t, a, frames, p0, p1, b, dist_scale_factor, do_search, w,
output_inter[i], output_intra[i] };
t->i_threadslice_start = ((h->mb.i_mb_height * i + h->param.i_lookahead_threads/2) / h->param.i_lookahead_threads);
t->i_threadslice_end = ((h->mb.i_mb_height * (i+1) + h->param.i_lookahead_threads/2) / h->param.i_lookahead_threads);
//起始到结束的宏块编码序号
int thread_height = t->i_threadslice_end - t->i_threadslice_start;
int thread_output_size = thread_height + NUM_INTS;
memset( output_inter[i], 0, thread_output_size * sizeof(int) );
memset( output_intra[i], 0, thread_output_size * sizeof(int) );
output_inter[i][NUM_ROWS] = output_intra[i][NUM_ROWS] = thread_height;
output_inter[i+1] = output_inter[i] + thread_output_size + PAD_SIZE;
output_intra[i+1] = output_intra[i] + thread_output_size + PAD_SIZE;
x264_threadpool_run( h->lookaheadpool, (void*)x264_slicetype_slice_cost, &s[i] );
}
for( int i = 0; i < h->param.i_lookahead_threads; i++ )
x264_threadpool_wait( h->lookaheadpool, &s[i] );
lookahead_threads值
if( h->param.b_sliced_threads )//slice_threads =1时
h->param.i_lookahead_threads = h->param.i_threads;
sync_lookahead 设置了这个值，意味着更低的线程优先级。
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