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-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).

Tuning

There are a few --tune options available, which are applied after the preset.

Note

The psnr and ssim tune options disable all optimizations that sacrafice metric scores for perceived visual quality (also known as psycho-visual optimizations). By default x265 always tunes for highest perceived visual quality but if one intends to measure an encode using PSNR or SSIM for the purpose of benchmarking, we highly recommend you configure x265 to tune for that particular metric.

–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