looked up what changed and from the looks of it this:
Code:
895 if( h->param.i_lookahead_threads == X264_THREADS_AUTO )
896 {
897 if( h->param.b_sliced_threads )
898 h->param.i_lookahead_threads = h->param.i_threads;
899 else
900 {
901 /* If we're using much slower lookahead settings than encoding settings, it helps a lot to use
902 * more lookahead threads. This typically happens in the first pass of a two-pass encode, so
903 * try to guess at this sort of case.
904 *
905 * Tuned by a little bit of real encoding with the various presets. */
906 int badapt = h->param.i_bframe_adaptive == X264_B_ADAPT_TRELLIS;
907 int subme = X264_MIN( h->param.analyse.i_subpel_refine / 3, 3 ) + (h->param.analyse.i_subpel_refine > 1);
908 int bframes = X264_MIN( (h->param.i_bframe - 1) / 3, 3 );
909
910 /* [b-adapt 0/1 vs 2][quantized subme][quantized bframes] */
911 static const uint8_t lookahead_thread_div[2][5][4] =
912 {{{6,6,6,6}, {3,3,3,3}, {4,4,4,4}, {6,6,6,6}, {12,12,12,12}},
913 {{3,2,1,1}, {2,1,1,1}, {4,3,2,1}, {6,4,3,2}, {12, 9, 6, 4}}};
914
915 h->param.i_lookahead_threads = h->param.i_threads / lookahead_thread_div[badapt][subme][bframes];
916 /* Since too many lookahead threads significantly degrades lookahead accuracy, limit auto
917 * lookahead threads to about 8 macroblock rows high each at worst. This number is chosen
918 * pretty much arbitrarily. */
919 h->param.i_lookahead_threads = X264_MIN( h->param.i_lookahead_threads, h->param.i_height / 128 );
920 }
921 }
source:
http://git.videolan.org/?p=x264.git;...b808f9ae3189e1
should be the interesting part, for those who want to know how x264 calculated the lookahead threads now
