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):
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 |
