libx264, libx264rgb


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 x264 project website is at .

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 for easy migration.

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 .

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 kilobits/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.

'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 CABAC.

'vlc'

Enable CAVLC 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 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 -c:v 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).