Thursday, April 24, 2014

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.

ultrafastsuperfastveryfastfasterfastmediumslowslowerveryslowplacebo
ctu32323264646464646464
bframes4444444888
b-adapt0000222222
rc-lookahead10101515152025304060
scenecut0404040404040404040
refs1111333355
mediahexhexhexhexhexstarstarstarstar
merange25445757575757575792
subme0112223345
rect0000001111
amp0000000111
max-merge2222223345
early-skip1111000000
fast-intra1111100000
fast-cbf1111000000
sao0111111111
signhide0111111111
weightp0011111111
aq-mode0022222222
cuTree0000111111
rdLevel2222234666
lft0111111111
tu-intra1111111234
tu-inter1111111234

Placebo mode further enables transform-skip prediction analysis (lossless).
–tuneeffect
psnrdisables adaptive quant, psy-rd, and cutree
ssimenables adaptive quant auto-mode, disables psy-rd
fastdecodeno loop filters, no weighted pred, no intra in B
zerolatencyno lookahead, no B frames, no cutree

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