H.265 Presets

x265 has a number of predefined --preset options that make trade-offs between encode speed (encoded frames per second) and compression efficiency (quality per bit in the bitstream). The default preset is medium, it does a reasonably good job of finding the best possible quality without spending enormous CPU cycles looking for the absolute most efficient way to achieve that quality. As you go higher than medium, the encoder takes shortcuts to improve performance at the expense of quality and compression efficiency. As you go lower than medium, the encoder tries harder and harder to achieve the best quailty per bit compression ratio.

The presets adjust encoder parameters to affect these trade-offs.

	ultrafast	superfast	veryfast	faster	fast	medium	slow	slower	veryslow	placebo
ctu	32	32	32	64	64	64	64	64	64	64
bframes	4	4	4	4	4	4	4	8	8	8
b-adapt	0	0	0	0	2	2	2	2	2	2
rc-lookahead	10	10	15	15	15	20	25	30	40	60
scenecut	0	40	40	40	40	40	40	40	40	40
refs	1	1	1	1	3	3	3	3	5	5
me	dia	hex	hex	hex	hex	hex	star	star	star	star
merange	25	44	57	57	57	57	57	57	57	92
subme	0	1	1	2	2	2	3	3	4	5
rect	0	0	0	0	0	0	1	1	1	1
amp	0	0	0	0	0	0	0	1	1	1
max-merge	2	2	2	2	2	2	3	3	4	5
early-skip	1	1	1	1	0	0	0	0	0	0
fast-intra	1	1	1	1	1	0	0	0	0	0
fast-cbf	1	1	1	1	0	0	0	0	0	0
sao	0	1	1	1	1	1	1	1	1	1
signhide	0	1	1	1	1	1	1	1	1	1
weightp	0	0	1	1	1	1	1	1	1	1
aq-mode	0	0	2	2	2	2	2	2	2	2
cuTree	0	0	0	0	1	1	1	1	1	1
rdLevel	2	2	2	2	2	3	4	6	6	6
lft	0	1	1	1	1	1	1	1	1	1
tu-intra	1	1	1	1	1	1	1	2	3	4
tu-inter	1	1	1	1	1	1	1	2	3	4

Placebo mode further enables transform-skip prediction analysis (lossless).

–tune	effect
psnr	disables adaptive quant, psy-rd, and cutree
ssim	enables adaptive quant auto-mode, disables psy-rd
fastdecode	no loop filters, no weighted pred, no intra in B
zerolatency	no lookahead, no B frames, no cutree