A significant number of options are exposed for defining the cadence of frames, within a decodable segment of time referred to as a GOP (Group of Pictures.) By default, output will have variable length GOPs optimized around detection of scene changes, with each GOP at least 25 frames in length between IDR frames.

It is possible to force fixed GOPs by setting keyint and keyint_min to the same number. This is frequently helpful when using adaptive bitrate packages so segments align. To disable non-IDR scenecut keyframes, you can also set sc_threshold to zero.

Parameter	Description	Allowed Values	Default Value
keyint_min	Specify the minimum distance between I-frames.	Positive integer number	none (automatically determined by codec)
level	As set of constraints that specify decoder performance for a profile.	Positive integer number	high profile, main profile, iphone_stream, roku: 30(3.0) baseline profile: 13(1.3)
open-gop	Use recovery points to close GOPs, only available with b-frames	1, 0	none
sc_threshold	Specify the sensitivity of x264's scenecut detection.	Positive integer number	40
bf	Specify the number of b-frames.	Positive integer number	16
b_strategy	Adaptively decides through a low-resolution lookahead the best number of B-frames.	0, 1, 2	1
coder	CABAC is the default entropy encoder used by x264.	0, 1	1(CABAC enabled)
refs	Specify how many references can be used, through a maximum of 16.	Positive integer number	baseline profile: 3 main profile: 6 high profile: 4
flags	Enable or disable the loop filter.	-loop/+loop, -psnr/+psnr	+loop (Enabled)
deblockalpha, deblockbeta	One of H.264's main features is the in-loop deblocker, which avoids the problem of blocking artifacts disrupting motion estimation.	Positive integer number	0 (Must have '-flags +loop')
directpred	Specify the direct MV prediction mode.	0 — none, 1 — spatial 2 — temporal 3 — auto	main, high, baseline, smooth_streaming — 1, roku — 3
aq-strength	Specify the amount of Adaptive Quantization(AQ) that is applied to the frames.	Positive float number 0.5 – low AQ 1.5 – strong AQ	1.0
force-cfr	Enable constant framerate.	1, 0	0

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For level parameter
Drop the decimal, for example 3.0 is 30, 1.3 is 13.