Testing x264 b-frames heuristic

Last week I wrote about my x264 patch that would enable B-frames heuristic decisions in x264.

Today I finally managed to do some proper testing using the Big Buck Bunny PNG image sequence from xiph.org, and found out that for reasonable settings (b-frames 8, b-heuristic 4) we have an overall 4% speed gain and for more extreme settings (b-frames 16, b-heuristic 4) we gain 17% overall.

The base command line used in this test is –b-adapt 2 –b-pyramid -r 4 –crf 26 -A all –direct auto -w -m 9 –psy-rd –mixed-refs -8 -t 2 –threads 3 –thread-input.

In the following pretty graph™ I plotted the frames-per-second for various settings (b-frames/b-heuristic):

Spped results for different x264 encodes

The following are the raw results taken from the x264 logs:

settings PSNR SSIM
b-frames b-heuristic fps kb/s Y avg global
4 0 12,62 336,03 39,644 40,377 38,614 0,9686156
4 2 12,67 336,95 39,650 40,383 38,617 0,9686125
8 0 11,16 333,68 39,604 40,330 38,583 0,9683932
8 2 12,07 335,57 39,631 40,356 38,598 0,9685096
8 4 11,64 334,02 39,613 40,338 38,588 0,9684230
16 0 8,43 331,42 39,588 40,313 38,566 0,9682979
16 2 10,17 334,85 39,619 40,341 38,590 0,9684408
16 4 9,93 333,50 39,607 40,330 38,585 0,9683999
16 8 9,31 333,11 39,598 40,322 38,579 0,9683561
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