The x264 Project has lead the way on H.264 development by introducing many key features. Variance Adaptive Quantization (VAQ) and Rate–Distortion Optimization (RDO) attempt to preserve video quality and motion estimation against the amount of data required to encode the video. Advanced controls include options for GOP structure, keyframing, scene detection, macroblocking, and interframe quantization. Many of these features are discussed in depth on the x264 forums. A list of the x264 flags available to our API follows:
Frame-type options:
keyint_min [optional] – The minimum distance between I-frames.
Allowed values: integer
Default: 25
sc_threshold [optional] – Adjusts the sensitivity of x264's scenecut detection.
Allowed values: integer
Default: 40
bf [optional] – B-frames.
Allowed values: integer
Default: 16
b_strategy [optional] – Adaptively decides through a low-resolution lookahead the best number of B-frames to use.
Allowed values: 0,1,2
Default: 1
flags2 [optional] – Allows B-frames to be kept as references.
Allowed values: +bpyramid, +wpred, +mixed_refs, +dct8×8, -fastpskip/+fastpskip, +aud.
Default: None
coder [optional] – CABAC is the default entropy encoder used by x264.
Allowed values: 0,1
Default: 1(CABAC enabled)
refs [optional] – This parameter lets one specify how many references can be used, through a maximum of 16.
Allowed values: integer
Default: 6
flags [optional] – Disable loop filter.
Allowed values: -loop/+loop,-psnr/+psnr
Default: +loop (Enabled)
deblockalpha, deblockbeta [optional] – One of H.264's main features is the in-loop deblocker, which avoids the problem of blocking artifacts disrupting motion estimation.
Allowed values: integer
Default: 0 (Must have '-flags +loop')
Ratecontrol:
cqp [optional] – Constant quantizer mode.
Allowed values: integer
Default: None
crf [optional] – Constant quality mode (also known as constant ratefactor).
Allowed values: float
Default: None
qmin [optional] – Minimum quantizer.
Allowed values: integer
Default: 10
qmax [optional] – Maximum quantizer.
Allowed values: integer
Default: 50
qdiff [optional] – Set max QP step.
Allowed values: integer
Default: 4
bt [optional] – Allowed variance of average bitrate.
Allowed values: integer
Default: None
i_qfactor [optional] – Qscale difference between I-frames and P-frames.
Allowed values: float
Default: 0.71
b_qfactor [optional] – Qscale difference between P-frames and B-frames.
Allowed values: float
Default: None
chromaoffset [optional] – QP difference between chroma and luma.
Allowed values: integer
Default: None
pass [optional]
Allowed values: <1,2,3>
Default: None
rc_eq [optional] – Ratecontrol equation.
Allowed values: string
Default: blurCplx^(1-qComp)
qcomp [optional] – QP curve compression: 0.0 => CBR, 1.0 => CQP.
Allowed values: float
Default: 0.60
complexityblur [optional] – Reduce fluctuations in QP (before curve compression).
Allowed values: float
Default: 20.0
qblur [optional] – Reduce fluctuations in QP (after curve compression) .
Allowed values: float
Default: 0.5
Analysis:
partitions [optional] – One of H.264's most useful features is the ability to choose among many combinations of inter and intra partitions.
Allowed values: +partp8x8,+partp4x4,+partb8x8,+parti8x8,+parti4x4
Default: None
directpred [optional]
Allowed values: integer
Default: None
flags2 [optional] – This allows B-frames to use weighted prediction options other than the default. There is no real speed cost for this, so it should always be enabled.
Allowed values: +bpyramid,+wpred,+mixed_refs,+dct8×8,-fastpskip/+fastpskip,–no-fast-pskip/nothing,+aud.
Default: +wpred
me_method [optional]
Allowed values: <epzs,hex,umh,full>
Default: None
me_range [optional] – MErange controls the max range of the motion search.
Allowed values: integer
Default:16
subq [optional] – MErange controls the max range of the motion search.
Allowed values: integer
Default: 6
trellis [optional] – Trellis chooses the optimal rounding choices for the maximum rate-distortion score, to maximize PSNR relative to bitrate.
Allowed values: <0,1,2>
Default: None
(4 votes, average: 4.50 out of 5)
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