doc/encoders: partially rewrite and reformat libx264 docs

Format is based on the thread:
"[PATCH] doc/encoders: Add libopus encoder doc" (06-28-2013)
http://thread.gmane.org/gmane.comp.video.ffmpeg.devel/165368/

Also merge the two option sections (Mapping and Private options).

Patch partially edited by Stefano Sabatini.

Signed-off-by: Stefano Sabatini <stefasab@gmail.com>
(cherry picked from commit 11cb697501)

Signed-off-by: Timothy Gu <timothygu99@gmail.com>

doc/encoders.texi

@@ -844,178 +844,318 @@ For more information about libvpx see:
 
 x264 H.264/MPEG-4 AVC encoder wrapper
 
-Requires the presence of the libx264 headers and library during
-configuration. You need to explicitly configure the build with
+This encoder requires the presence of the libx264 headers and library
+during configuration. You need to explicitly configure the build with
 @code{--enable-libx264}.
 
-x264 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).
+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).
 
-The FFmpeg wrapper provides a mapping for most of them using global options
-that match those of the encoders and provides private options for the unique
-encoder options. Additionally an expert override is provided to directly pass
-a list of key=value tuples as accepted by x264_param_parse.
+Many libx264 encoder options are mapped to FFmpeg global codec
+options, while unique encoder options are provided through private
+options. Additionally the @option{x264opts} and @option{x264-params}
+private options allows to pass a list of key=value tuples as accepted
+by the libx264 @code{x264_param_parse} function.
 
-@subsection Option Mapping
+The x264 project website is at
+@url{http://www.videolan.org/developers/x264.html}.
 
-The following options are supported by the x264 wrapper, the x264-equivalent
-options follow the FFmpeg ones.
+@subsection Options
 
-@multitable @columnfractions .2 .2
-@item b                 @tab bitrate
-FFmpeg @code{b} option is expressed in bits/s, x264 @code{bitrate} in kilobits/s.
-@item bf                @tab bframes
-Maximum number of B-frames.
-@item g                 @tab keyint
-Maximum GOP size.
-@item qmin              @tab qpmin
-@item qmax              @tab qpmax
-@item qdiff             @tab qpstep
-@item qblur             @tab qblur
-@item qcomp             @tab qcomp
-@item refs              @tab ref
-@item sc_threshold      @tab scenecut
-@item trellis           @tab trellis
-@item nr                @tab nr
-Noise reduction.
-@item me_range          @tab merange
-@item me_method         @tab me
-@item subq              @tab subme
-@item b_strategy        @tab b-adapt
-@item keyint_min        @tab keyint-min
-@item coder             @tab cabac
-Set coder to @code{ac} to use CABAC.
-@item cmp               @tab chroma-me
-Set to @code{chroma} to use chroma motion estimation.
-@item threads           @tab threads
-@item thread_type       @tab sliced_threads
-Set to @code{slice} to use sliced threading instead of frame threading.
-@item flags -cgop       @tab open-gop
-Set @code{-cgop} to use recovery points to close GOPs.
-@item rc_init_occupancy @tab vbv-init
-Initial buffer occupancy.
-@end multitable
+The following options are supported by the libx264 wrapper. The
+@command{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
+@ref{codec-options}.
+
+To get a more accurate and extensive documentation of the libx264
+options, invoke the command @command{x264 --full-help} or consult
+the libx264 documentation.
 
-@subsection Private Options
 @table @option
-@item -preset @var{string}
-Set the encoding preset (cf. x264 --fullhelp).
-@item -tune @var{string}
-Tune the encoding params (cf. x264 --fullhelp).
-@item -profile @var{string}
-Set profile restrictions (cf. x264 --fullhelp).
-@item -fastfirstpass @var{integer}
-Use fast settings when encoding first pass.
-@item -crf @var{float}
-Select the quality for constant quality mode.
-@item -crf_max @var{float}
-In CRF mode, prevents VBV from lowering quality beyond this point.
-@item -qp @var{integer}
-Constant quantization parameter rate control method.
-@item -aq-mode @var{integer}
-AQ method
+@item b (@emph{bitrate})
+Set bitrate in bits/s. Note that FFmpeg's @option{b} option is
+expressed in bits/s, while @command{x264}'s @option{bitrate} is in
+kilobits/s.
+
+@item bf (@emph{bframes})
+
+@item g (@emph{keyint})
+
+@item qmax (@emph{qpmax})
+
+@item qmin (@emph{qpmin})
+
+@item qdiff (@emph{qpstep})
+
+@item qblur (@emph{qblur})
+
+@item qcomp (@emph{qcomp})
+
+@item refs (@emph{ref})
+
+@item sc_threshold (@emph{scenecut})
+
+@item trellis (@emph{trellis})
+
+@item nr  (@emph{nr})
+
+@item me_range (@emph{merange})
+
+@item me_method (@emph{me})
+Set motion estimation method. Possible values in the decreasing order
+of speed:
 
-Possible values:
 @table @samp
-@item none
+@item dia (@emph{dia})
+@item epzs (@emph{dia})
+Diamond search with radius 1 (fastest). @samp{epzs} is an alias for
+@samp{dia}.
+@item hex (@emph{hex})
+Hexagonal search with radius 2.
+@item umh (@emph{umh})
+Uneven multi-hexagon search.
+@item esa (@emph{esa})
+Exhaustive search.
+@item tesa (@emph{tesa})
+Hadamard exhaustive search (slowest).
+@end table
 
-@item variance
+@item subq (@emph{subme})
+
+@item b_strategy (@emph{b-adapt})
+
+@item keyint_min (@emph{min-keyint})
+
+@item coder
+Set entropy encoder. Possible values:
+
+@table @samp
+@item ac
+Enable CABAC.
+
+@item vlc
+Enable CAVLC and disable CABAC. It generates the same effect as
+@command{x264}'s @option{--no-cabac} option.
+@end table
+
+@item cmp
+Set full pixel motion estimation comparation algorithm. Possible values:
+
+@table @samp
+@item chroma
+Enable chroma in motion estimation.
+
+@item sad
+Ignore chroma in motion estimation. It generates the same effect as
+@command{x264}'s @option{--no-chroma-me} option.
+@end table
+
+@item threads (@emph{threads})
+
+@item thread_type
+Set multithreading technique. Possible values:
+
+@table @samp
+@item slice
+Slice-based multithreading. It generates the same effect as
+@command{x264}'s @option{--sliced-threads} option.
+@item frame
+Frame-based multithreading.
+@end table
+
+@item flags
+Set encoding flags. It can be used to disable closed GOP and enable
+open GOP by setting it to @code{-cgop}. The result is similar to
+the behavior of @command{x264}'s @option{--open-gop} option.
+
+@item rc_init_occupancy (@emph{vbv-init})
+
+@item preset (@emph{preset})
+Set the encoding preset.
+
+@item tune (@emph{tune})
+Set tuning of the encoding params.
+
+@item profile (@emph{profile})
+Set profile restrictions.
+
+@item fastfirstpass
+Enable fast settings when encoding first pass, when set to 1. When set
+to 0, it has the same effect of @command{x264}'s
+@option{--slow-firstpass} option.
+
+@item crf (@emph{crf})
+Set the quality for constant quality mode.
+
+@item crf_max (@emph{crf-max})
+In CRF mode, prevents VBV from lowering quality beyond this point.
+
+@item qp (@emph{qp})
+Set constant quantization rate control method parameter.
+
+@item aq-mode (@emph{aq-mode})
+Set AQ method. Possible values:
+
+@table @samp
+@item none (@emph{0})
+Disabled.
+
+@item variance (@emph{1})
 Variance AQ (complexity mask).
-@item autovariance
+
+@item autovariance (@emph{2})
 Auto-variance AQ (experimental).
 @end table
-@item -aq-strength @var{float}
-AQ strength, reduces blocking and blurring in flat and textured areas.
-@item -psy @var{integer}
-Use psychovisual optimizations.
-@item -psy-rd @var{string}
-Strength of psychovisual optimization, in <psy-rd>:<psy-trellis> format.
-@item -rc-lookahead @var{integer}
-Number of frames to look ahead for frametype and ratecontrol.
-@item -weightb @var{integer}
-Weighted prediction for B-frames.
-@item -weightp @var{integer}
-Weighted prediction analysis method.
 
-Possible values:
+@item aq-strength (@emph{aq-strength})
+Set AQ strength, reduce blocking and blurring in flat and textured areas.
+
+@item psy
+Use psychovisual optimizations when set to 1. When set to 0, it has the
+same effect as @command{x264}'s @option{--no-psy} option.
+
+@item psy-rd  (@emph{psy-rd})
+Set strength of psychovisual optimization, in
+@var{psy-rd}:@var{psy-trellis} format.
+
+@item rc-lookahead (@emph{rc-lookahead})
+Set number of frames to look ahead for frametype and ratecontrol.
+
+@item weightb
+Enable weighted prediction for B-frames when set to 1. When set to 0,
+it has the same effect as @command{x264}'s @option{--no-weightb} option.
+
+@item weightp (@emph{weightp})
+Set weighted prediction method for P-frames. Possible values:
+
 @table @samp
-@item none
-
-@item simple
-
-@item smart
-
+@item none (@emph{0})
+Disabled
+@item simple (@emph{1})
+Enable only weighted refs
+@item smart (@emph{2})
+Enable both weighted refs and duplicates
 @end table
-@item -ssim @var{integer}
-Calculate and print SSIM stats.
-@item -intra-refresh @var{integer}
-Use Periodic Intra Refresh instead of IDR frames.
-@item -b-bias @var{integer}
-Influences how often B-frames are used.
-@item -b-pyramid @var{integer}
-Keep some B-frames as references.
 
-Possible values:
+@item ssim (@emph{ssim})
+Enable calculation and printing SSIM stats after the encoding.
+
+@item intra-refresh (@emph{intra-refresh})
+Enable the use of Periodic Intra Refresh instead of IDR frames when set
+to 1.
+
+@item b-bias (@emph{b-bias})
+Set the influence on how often B-frames are used.
+
+@item b-pyramid (@emph{b-pyramid})
+Set method for keeping of some B-frames as references. Possible values:
+
 @table @samp
-@item none
-
-@item strict
+@item none (@emph{none})
+Disabled.
+@item strict (@emph{strict})
 Strictly hierarchical pyramid.
-@item normal
+@item normal (@emph{normal})
 Non-strict (not Blu-ray compatible).
 @end table
-@item -mixed-refs @var{integer}
-One reference per partition, as opposed to one reference per macroblock.
-@item -8x8dct @var{integer}
-High profile 8x8 transform.
-@item -fast-pskip @var{integer}
-@item -aud @var{integer}
-Use access unit delimiters.
-@item -mbtree @var{integer}
-Use macroblock tree ratecontrol.
-@item -deblock @var{string}
-Loop filter parameters, in <alpha:beta> form.
-@item -cplxblur @var{float}
-Reduce fluctuations in QP (before curve compression).
-@item -partitions @var{string}
-A comma-separated list of partitions to consider, possible values: p8x8, p4x4, b8x8, i8x8, i4x4, none, all.
-@item -direct-pred @var{integer}
-Direct MV prediction mode
 
-Possible values:
+@item 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 @command{x264}'s @option{--no-mixed-refs} option.
+
+@item 8x8dct
+Enable adaptive spatial transform (high profile 8x8 transform)
+when set to 1. When set to 0, it has the same effect as
+@command{x264}'s @option{--no-8x8dct} option.
+
+@item fast-pskip
+Enable early SKIP detection on P-frames when set to 1. When set
+to 0, it has the same effect as @command{x264}'s
+@option{--no-fast-pskip} option.
+
+@item aud (@emph{aud})
+Enable use of access unit delimiters when set to 1.
+
+@item mbtree
+Enable use macroblock tree ratecontrol when set to 1. When set
+to 0, it has the same effect as @command{x264}'s
+@option{--no-mbtree} option.
+
+@item deblock (@emph{deblock})
+Set loop filter parameters, in @var{alpha}:@var{beta} form.
+
+@item cplxblur (@emph{cplxblur})
+Set fluctuations reduction in QP (before curve compression).
+
+@item partitions (@emph{partitions})
+Set partitions to consider as a comma-separated list of. Possible
+values in the list:
+
 @table @samp
-@item none
-
-@item spatial
-
-@item temporal
-
-@item auto
-
-@end table
-@item -slice-max-size @var{integer}
-Limit the size of each slice in bytes.
-@item -stats @var{string}
-Filename for 2 pass stats.
-@item -nal-hrd @var{integer}
-Signal HRD information (requires vbv-bufsize; cbr not allowed in .mp4).
-
-Possible values:
-@table @samp
-@item none
-
-@item vbr
-
-@item cbr
-
+@item p8x8
+8x8 P-frame partition.
+@item p4x4
+4x4 P-frame partition.
+@item b8x8
+4x4 B-frame partition.
+@item i8x8
+8x8 I-frame partition.
+@item i4x4
+4x4 I-frame partition.
+(Enabling @samp{p4x4} requires @samp{p8x8} to be enabled. Enabling
+@samp{i8x8} requires adaptive spatial transform (@option{8x8dct}
+option) to be enabled.)
+@item none (@emph{none})
+Do not consider any partitions.
+@item all (@emph{all})
+Consider every partition.
 @end table
 
-@item x264opts @var{options}
-Allow to set any x264 option, see @code{x264 --fullhelp} for a list.
+@item direct-pred (@emph{direct})
+Set direct MV prediction mode. Possible values:
 
-@var{options} is a list of @var{key}=@var{value} couples separated by
+@table @samp
+@item none (@emph{none})
+Disable MV prediction.
+@item spatial (@emph{spatial})
+Enable spatial predicting.
+@item temporal (@emph{temporal})
+Enable temporal predicting.
+@item auto (@emph{auto})
+Automatically decided.
+@end table
+
+@item slice-max-size (@emph{slice-max-size})
+Set the limit of the size of each slice in bytes. If not specified
+but RTP payload size (@option{ps}) is specified, that is used.
+
+@item stats (@emph{stats})
+Set the file name for multi-pass stats.
+
+@item nal-hrd (@emph{nal-hrd})
+Set signal HRD information (requires @option{vbv-bufsize} to be set).
+Possible values:
+
+@table @samp
+@item none (@emph{none})
+Disable HRD information signaling.
+@item vbr (@emph{vbr})
+Variable bit rate.
+@item cbr (@emph{cbr})
+Constant bit rate (not allowed in MP4 container).
+@end table
+
+@item x264opts (N.A.)
+Set any x264 option, see @command{x264 --fullhelp} for a list.
+
+Argument is a list of @var{key}=@var{value} couples separated by
 ":". In @var{filter} and @var{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.
@@ -1025,17 +1165,22 @@ For example to specify libx264 encoding options with @command{ffmpeg}:
 ffmpeg -i foo.mpg -vcodec libx264 -x264opts keyint=123:min-keyint=20 -an out.mkv
 @end example
 
-For more information about libx264 and the supported options see:
-@url{http://www.videolan.org/developers/x264.html}
+@item x264-params (N.A.)
+Override the x264 configuration using a :-separated list of key=value
+parameters.
 
-@item -x264-params @var{string}
-Override the x264 configuration using a :-separated list of key=value parameters.
+This option is functionally the same as the @option{x264opts}, but is
+duplicated for compability with the Libav fork.
+
+For example to specify libx264 encoding options with @command{ffmpeg}:
 @example
--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
+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
 @end example
 @end table
 
-Encoding avpresets for common usages are provided so they can be used with the
-general presets system (e.g. passing the @code{-pre} option).
+Encoding ffpresets for common usages are provided so they can be used with the
+general presets system (e.g. passing the @option{pre} option).
 
 @c man end VIDEO ENCODERS