x264 H.264/MPEG-4 AVC encoder wrapper.
This encoder requires the presence of the libx264 headers and library during configuration. You need to explicitly configure the build with
--enable-libx264
.
libx264 supports an impressive number of features, including 8x8 and 4x4 adaptive spatial transform, adaptive B-frame placement, CAVLC/CABAC entropy coding, interlacing (MBAFF), lossless mode, psy optimizations for detail retention (adaptive quantization, psy-RD, psy-trellis).
Many libx264 encoder options are mapped to FFmpeg global codec options,
while unique encoder options are provided through
private options.
Additionally the
x264opts
and
x264-params
private options allows one to pass a list of key=value tuples as accepted by the libx264
x264_param_parse
function.
The libx264rgb encoder
is the same as
libx264, except it accepts packed RGB pixel formats as input instead of YUV.
x264 supports 8- to 10-bit color spaces. The exact bit depth is controlled at x264’s configure time. FFmpeg only supports one bit depth in one particular build. In other words, it is not possible to build one FFmpeg with multiple versions of x264 with different bit depths.
The following options are supported by the libx264 wrapper. The
x264
-equivalent options or values are listed in parentheses
括號
for easy migration.
括號里面對應x264的選項
To reduce the duplication of documentation, only the private options and some others requiring special attention are documented here.
For the documentation of the undocumented generic options,
see
the Codec Options chapter
.
To get a more accurate and extensive documentation of the libx264 options, invoke the command
x264 --fullhelp
or consult the libx264 documentation.
b (
bitrate
)
Set bitrate in bits/s.
Note that FFmpeg’s
b
option is expressed in bits/s, while
x264
’s
bitrate
is in
kilo
bits/s.
bf (
bframes
)
g (
keyint
)
qmin (
qpmin
)
Minimum quantizer scale.
qmax (
qpmax
)
Maximum quantizer scale.
qdiff (
qpstep
)
Maximum difference between quantizer scales.
qblur (
qblur
)
Quantizer curve blur
qcomp (
qcomp
)
Quantizer curve compression factor
refs (
ref
)
Number of reference frames each P-frame can use. The range is from
0-16
.
sc_threshold (
scenecut
)
Sets the threshold for the scene change detection.
trellis (
trellis
)
Performs Trellis quantization to increase efficiency. Enabled by default.
nr (
nr
)
me_range (
merange
)
Maximum range of the motion search in pixels.
me_method (
me
)
Set motion estimation method. Possible values in the decreasing order of speed:
‘
dia (
dia
)
’
‘
epzs (
dia
)
’
Diamond search with radius 1 (fastest). ‘
epzs
’ is an alias for ‘
dia
’.
‘
hex (
hex
)
’
Hexagonal search with radius 2.
‘
umh (
umh
)
’
Uneven multi-hexagon search.
‘
esa (
esa
)
’
Exhaustive search.
窮舉搜索
‘
tesa (
tesa
)
’
Hadamard exhaustive search (slowest).
forced-idr
Normally, when forcing a I-frame type, the encoder can select any type of I-frame. This option forces it to choose an IDR-frame.
subq (
subme
)
Sub-pixel motion estimation method.
b_strategy (
b-adapt
)
Adaptive B-frame placement decision algorithm. Use only on first-pass.
keyint_min (
min-keyint
)
Minimum GOP size.
coder
Set entropy encoder. Possible values:
‘
ac
’
Enable CA
BAC
.
‘
vlc
’
Enable CA
VLC
and disable CABAC. It generates the same effect as
x264
’s
--no-cabac
option.
cmp
Set full pixel motion estimation comparison algorithm. Possible values:
‘
chroma
’
Enable chroma in motion estimation.
‘
sad
’
Ignore chroma in motion estimation. It generates the same effect as
x264
’s
--no-chroma-me
option.
threads (
threads
)
Number of encoding threads.
thread_type
Set multithreading technique. Possible values:
‘
slice
’
Slice-based multithreading. It generates the same effect as
x264
’s
--sliced-threads
option.
‘
frame
’
Frame-based multithreading.
flags
Set encoding flags. It can be used to disable closed GOP and enable
open GOP
by setting it to
-cgop
. The result is similar to the behavior of
x264
’s
--open-gop
option.
rc_init_occupancy (
vbv-init
)
preset (
preset
)
Set the encoding preset.
tune (
tune
)
Set tuning of the encoding params.
profile (
profile
)
Set profile restrictions.
fastfirstpass
Enable fast settings when encoding first pass, when set to 1. When set to 0, it has the same effect of
x264
’s
--slow-firstpass
option.
crf (
crf
)
Set the quality for constant quality mode.
crf_max (
crf-max
)
In CRF mode, prevents VBV from lowering quality beyond this point.
qp (
qp
)
Set constant quantization rate control method parameter.
aq-mode (
aq-mode
)
Set AQ method. Possible values:
‘
none (
0
)
’
Disabled.
‘
variance (
1
)
’
Variance AQ (complexity mask).
‘
autovariance (
2
)
’
Auto-variance AQ (experimental).
aq-strength (
aq-strength
)
Set AQ strength, reduce blocking and blurring in flat and textured areas.
psy
Use psychovisual optimizations when set to 1. When set to 0, it has the same effect as
x264
’s
--no-psy
option.
psy-rd (
psy-rd
)
Set strength of psychovisual optimization, in
psy-rd
:
psy-trellis
format.
rc-lookahead (
rc-lookahead
)
Set number of frames to look ahead for frametype and ratecontrol.
weightb
Enable weighted prediction for B-frames when set to 1. When set to 0, it has the same effect as
x264
’s
--no-weightb
option.
weightp (
weightp
)
Set weighted prediction method for P-frames. Possible values:
‘
none (
0
)
’
Disabled
‘
simple (
1
)
’
Enable only weighted refs
‘
smart (
2
)
’
Enable both weighted refs and duplicates
ssim (
ssim
)
Enable calculation and printing SSIM stats after the encoding.
intra-refresh (
intra-refresh
)
Enable the use of Periodic
定期的
Intra Refresh instead of IDR frames when set to 1.
avcintra-class (
class
)
Configure the encoder to generate AVC-Intra. Valid values are 50,100 and 200
bluray-compat (
bluray-compat
)
Configure the encoder to be compatible with the bluray standard. It is a shorthand for setting "bluray-compat=1 force-cfr=1".
b-bias (
b-bias
)
Set the influence on how often B-frames are used.
b-pyramid (
b-pyramid
)
Set method for keeping of some B-frames as references. Possible values:
‘
none (
none
)
’
Disabled.
‘
strict (
strict
)
’
Strictly hierarchical pyramid.
‘
normal (
normal
)
’
Non-strict (not Blu-ray compatible).
mixed-refs
Enable the use of one reference per partition, as opposed to one reference per macroblock when set to 1. When set to 0, it has the same effect as
x264
’s
--no-mixed-refs
option.
8x8dct
Enable adaptive spatial transform (high profile 8x8 transform) when set to 1. When set to 0, it has the same effect as
x264
’s
--no-8x8dct
option.
fast-pskip
Enable early SKIP detection on P-frames when set to 1. When set to 0, it has the same effect as
x264
’s
--no-fast-pskip
option.
aud (
aud
)
Enable use of access unit delimiters when set to 1.
mbtree
Enable use macroblock tree ratecontrol when set to 1. When set to 0, it has the same effect as
x264
’s
--no-mbtree
option.
deblock (
deblock
)
Set loop filter parameters, in
alpha
:
beta
form.
cplxblur (
cplxblur
)
Set fluctuations reduction in QP (before curve compression).
partitions (
partitions
)
Set partitions to consider as a comma-separated list of. Possible values in the list:
‘
p8x8
’
8x8 P-frame partition.
‘
p4x4
’
4x4 P-frame partition.
‘
b8x8
’
4x4 B-frame partition.
‘
i8x8
’
8x8 I-frame partition.
‘
i4x4
’
4x4 I-frame partition. (Enabling ‘
p4x4
’ requires ‘
p8x8
’ to be enabled. Enabling ‘
i8x8
’ requires adaptive spatial transform (
8x8dct
option) to be enabled.)
‘
none (
none
)
’
Do not consider any partitions.
‘
all (
all
)
’
Consider every partition.
direct-pred (
direct
)
Set direct MV prediction mode. Possible values:
‘
none (
none
)
’
Disable MV prediction.
‘
spatial (
spatial
)
’
Enable spatial predicting.
‘
temporal (
temporal
)
’
Enable temporal predicting.
‘
auto (
auto
)
’
Automatically decided.
slice-max-size (
slice-max-size
)
Set the limit of the size of each slice in bytes. If not specified but RTP payload size (
ps
) is specified, that is used.
stats (
stats
)
Set the file name for multi-pass stats.
nal-hrd (
nal-hrd
)
Set signal HRD information (requires
vbv-bufsize
to be set).
Possible values:
‘
none (
none
)
’
Disable HRD information signaling.
‘
vbr
(
vbr
)
’
Variable bit rate.
‘
cbr
(
cbr
)
’
Constant bit rate (not allowed in MP4 container).
x264opts (N.A.)
Set any x264 option, see
x264 --fullhelp
for a list.
Argument is a list of
key
=
value
couples separated by ":". In
filter
and
psy-rd
options that use ":" as a separator themselves,
use "," instead
. They accept it as well since long ago but this is kept undocumented for some reason.
For example to specify libx264 encoding options with
ffmpeg
:
ffmpeg -i foo.mpg -vcodec libx264 -x264opts keyint=123:min-keyint=20 -an out.mkv
a53cc
boolean
Import closed captions (which must be ATSC compatible format) into output. Only the mpeg2 and h264 decoders provide these. Default is 1 (on).
x264-params
(N.A.)
Override the x264 configuration using a :-separated list of key=value parameters.
This option is functionally
the same as the
x264opts
, but is duplicated for compatibility with the Libav fork.
For example to specify libx264 encoding options with
ffmpeg
:
ffmpeg -i INPUT -c:v libx264
-x264-params
level=30:bframes=0:weightp=0:\ cabac=0:ref=1:
vbv-maxrate=768:vbv-bufsize=2000
:analyse=all:me=umh:\ no-fast-pskip=1:subq=6:8x8dct=0:trellis=0 OUTPUT
Encoding ffpresets for common usages are provided so they can be used with the general presets system (e.g. passing the
pre
option).
CBR設置
為輸出設置CBR,有三個參數必須設置為同一個值。
bitrate(-b option), minimal rate(-minrate), maximal rate(-maxrate)。maximal rate需要設置-bufsize選項。例如設置CBR為0.5Mbit/s。
ffmpeg -i in.avi
-b 0.5M -minrate 0.5M -maxrate 0.5M -bufsize 1M
output.mkv
- qscale的取值可以是0.01-255但實際使用超過50就很糟糕了
- -qscale 使用固定量化因子來量化視頻這個是在vbr模式的,前面有提到,越小質量越好,不要超過50,相關的參數還有-qmin --qmax用來設定最大最小可使用的量化值
- -qdiff 指定固定量化器因子允許的最大偏差
qblur 指定量化器模糊系數，可用范圍是0.0-1.0越大使得碼率在時間上分配的越平均
- -qcomp 指定視頻量化器壓縮系數，默認0.5
上面文檔
中括號后面對應的是x264的選項
| FFmpeg option | x264 option |
| -g <frames> | --keyint |
| -b <bits per second> | --bitrate |
| -bufsize <bits> | --vbv-bufsize |
| -maxrate <bits> | --vbv-maxrate |
| -pass <1,2,3> | --pass |
| -crf <float> | --crf |
| -cqp <int> | --qp |
| -bf <int> | --bframes |
| -coder <0,1> | --no-cabac |
| -bframebias <int> | --b-bias |
| -keyint_min <int> | --min-keyint |
| -sc_threshold <int> | --scenecut |
| -deblockalpha <int>-deblockbeta <int> | --deblock |
| -qmin <int> | --qpmin |
| -qmax <int> | --qpmax |
| -qdiff <int> | --qpstep |
| -qcomp <float> | --qcomp |
| -qblur <float> | --qblur |
| -complexityblur <float> | --cplxblur |
| -refs <int> | --ref |
| -directpred <int> | --direct |
| -me_method <epzs,hex,umh,full> | --me |
| -me_range <int> | --merange |
| -subq <int> | --subme |
| -bidir_refine <0,1> | --bime |
| -trellis <0,1,2> | --trellis |
| -nr <int> | --nr |
| -level <int> | --level |
| -bt <bits> | --ratetol = -bt / -b |
| -rc_init_occupancy <bits> | --vbv-init = -rc_init_occupancy / -bufsize |
| -i_qfactor <float> | --ipratio = 1 / -i_qfactor |
| -b_qfactor <float> | --pbratio |
| -chromaoffset <int> | --chroma-qp-offset |
| -rc_eq <string> | --rc_eq |
| -threads <int> | --threads |
| -cmp <-chroma/+chroma> | --no-chroma-me |
| -partitions | --partitions |
| +parti8×8 | i8×8 |
| +parti4×4 | i4×4 |
| +partp8×8 | p8×8 |
| +partp4×4 | p4×4 |
| +partb8×8 | b8×8 |
| -flags | |
| -loop/+loop | --no-deblock/–deblock |
| -psnr/+psnr | --no-psnr/nothing |
| -flags2 | |
| +bpyramid | --b-pyramid |
| +wpred | --weightb |
| +brdo | --b-rdo 我這里的ffmpeg已經不能用這個了 |
| +mixed_refs | --mixed-refs |
| +dct8×8 | --8×8dct |
| -fastpskip/+fastpskip | --no-fast-pskip |
| +aud | --aud |