path: root/doc/filters.texi

@chapter Filtergraph description
@c man begin FILTERGRAPH DESCRIPTION

A filtergraph is a directed graph of connected filters. It can contain
cycles, and there can be multiple links between a pair of
filters. Each link has one input pad on one side connecting it to one
filter from which it takes its input, and one output pad on the other
side connecting it to the one filter accepting its output.

Each filter in a filtergraph is an instance of a filter class
registered in the application, which defines the features and the
number of input and output pads of the filter.

A filter with no input pads is called a "source", a filter with no
output pads is called a "sink".

@section Filtergraph syntax

A filtergraph can be represented using a textual representation, which
is recognized by the @code{-vf} and @code{-af} options of the ff*
tools, and by the @code{avfilter_graph_parse()} function defined in
@file{libavfilter/avfiltergraph.h}.

A filterchain consists of a sequence of connected filters, each one
connected to the previous one in the sequence. A filterchain is
represented by a list of ","-separated filter descriptions.

A filtergraph consists of a sequence of filterchains. A sequence of
filterchains is represented by a list of ";"-separated filterchain
descriptions.

A filter is represented by a string of the form:
[@var{in_link_1}]...[@var{in_link_N}]@var{filter_name}=@var{arguments}[@var{out_link_1}]...[@var{out_link_M}]

@var{filter_name} is the name of the filter class of which the
described filter is an instance of, and has to be the name of one of
the filter classes registered in the program.
The name of the filter class is optionally followed by a string
"=@var{arguments}".

@var{arguments} is a string which contains the parameters used to
initialize the filter instance, and are described in the filter
descriptions below.

The list of arguments can be quoted using the character "'" as initial
and ending mark, and the character '\' for escaping the characters
within the quoted text; otherwise the argument string is considered
terminated when the next special character (belonging to the set
"[]=;,") is encountered.

The name and arguments of the filter are optionally preceded and
followed by a list of link labels.
A link label allows to name a link and associate it to a filter output
or input pad. The preceding labels @var{in_link_1}
... @var{in_link_N}, are associated to the filter input pads,
the following labels @var{out_link_1} ... @var{out_link_M}, are
associated to the output pads.

When two link labels with the same name are found in the
filtergraph, a link between the corresponding input and output pad is
created.

If an output pad is not labelled, it is linked by default to the first
unlabelled input pad of the next filter in the filterchain.
For example in the filterchain:
@example
nullsrc, split[L1], [L2]overlay, nullsink
@end example
the split filter instance has two output pads, and the overlay filter
instance two input pads. The first output pad of split is labelled
"L1", the first input pad of overlay is labelled "L2", and the second
output pad of split is linked to the second input pad of overlay,
which are both unlabelled.

In a complete filterchain all the unlabelled filter input and output
pads must be connected. A filtergraph is considered valid if all the
filter input and output pads of all the filterchains are connected.

Follows a BNF description for the filtergraph syntax:
@example
@var{NAME}             ::= sequence of alphanumeric characters and '_'
@var{LINKLABEL}        ::= "[" @var{NAME} "]"
@var{LINKLABELS}       ::= @var{LINKLABEL} [@var{LINKLABELS}]
@var{FILTER_ARGUMENTS} ::= sequence of chars (eventually quoted)
@var{FILTER}           ::= [@var{LINKNAMES}] @var{NAME} ["=" @var{ARGUMENTS}] [@var{LINKNAMES}]
@var{FILTERCHAIN}      ::= @var{FILTER} [,@var{FILTERCHAIN}]
@var{FILTERGRAPH}      ::= @var{FILTERCHAIN} [;@var{FILTERGRAPH}]
@end example

@c man end FILTERGRAPH DESCRIPTION

@chapter Audio Filters
@c man begin AUDIO FILTERS

When you configure your FFmpeg build, you can disable any of the
existing filters using --disable-filters.
The configure output will show the audio filters included in your
build.

Below is a description of the currently available audio filters.

@section aconvert

Convert the input audio format to the specified formats.

The filter accepts a string of the form:
"@var{sample_format}:@var{channel_layout}:@var{packing_format}".

@var{sample_format} specifies the sample format, and can be a string or
the corresponding numeric value defined in @file{libavutil/samplefmt.h}.

@var{channel_layout} specifies the channel layout, and can be a string
or the corresponding number value defined in @file{libavutil/chlayout.h}.

@var{packing_format} specifies the type of packing in output, can be one
of "planar" or "packed", or the corresponding numeric values "0" or "1".

The special parameter "auto", signifies that the filter will
automatically select the output format depending on the output filter.

Some examples follow.

@itemize
@item
Convert input to unsigned 8-bit, stereo, packed:
@example
aconvert=u8:stereo:packed
@end example

@item
Convert input to unsigned 8-bit, automatically select out channel layout
and packing format:
@example
aconvert=u8:auto:auto
@end example
@end itemize

@section aformat

Convert the input audio to one of the specified formats. The framework will
negotiate the most appropriate format to minimize conversions.

The filter accepts three lists of formats, separated by ":", in the form:
"@var{sample_formats}:@var{channel_layouts}:@var{packing_formats}".

Elements in each list are separated by "," which has to be escaped in the
filtergraph specification.

The special parameter "all", in place of a list of elements, signifies all
supported formats.

Some examples follow:
@example
aformat=u8\\,s16:mono:packed

aformat=s16:mono\\,stereo:all
@end example

@section anull

Pass the audio source unchanged to the output.

@section aresample

Resample the input audio to the specified sample rate.

The filter accepts exactly one parameter, the output sample rate. If not
specified then the filter will automatically convert between its input
and output sample rates.

For example, to resample the input audio to 44100Hz:
@example
aresample=44100
@end example

@section ashowinfo

Show a line containing various information for each input audio frame.
The input audio is not modified.

The shown line contains a sequence of key/value pairs of the form
@var{key}:@var{value}.

A description of each shown parameter follows:

@table @option
@item n
sequential number of the input frame, starting from 0

@item pts
presentation TimeStamp of the input frame, expressed as a number of
time base units. The time base unit depends on the filter input pad, and
is usually 1/@var{sample_rate}.

@item pts_time
presentation TimeStamp of the input frame, expressed as a number of
seconds

@item pos
position of the frame in the input stream, -1 if this information in
unavailable and/or meanigless (for example in case of synthetic audio)

@item fmt
sample format name

@item chlayout
channel layout description

@item nb_samples
number of samples (per each channel) contained in the filtered frame

@item rate
sample rate for the audio frame

@item planar
if the packing format is planar, 0 if packed

@item checksum
Adler-32 checksum (printed in hexadecimal) of all the planes of the input frame

@item plane_checksum
Adler-32 checksum (printed in hexadecimal) for each input frame plane,
expressed in the form "[@var{c0} @var{c1} @var{c2} @var{c3} @var{c4} @var{c5}
@var{c6} @var{c7}]"
@end table

@c man end AUDIO FILTERS

@chapter Audio Sources
@c man begin AUDIO SOURCES

Below is a description of the currently available audio sources.

@section abuffer

Buffer audio frames, and make them available to the filter chain.

This source is mainly intended for a programmatic use, in particular
through the interface defined in @file{libavfilter/asrc_abuffer.h}.

It accepts the following mandatory parameters:
@var{sample_rate}:@var{sample_fmt}:@var{channel_layout}:@var{packing}

@table @option

@item sample_rate
The sample rate of the incoming audio buffers.

@item sample_fmt
The sample format of the incoming audio buffers.
Either a sample format name or its corresponging integer representation from
the enum AVSampleFormat in @file{libavutil/samplefmt.h}

@item channel_layout
The channel layout of the incoming audio buffers.
Either a channel layout name from channel_layout_map in
@file{libavutil/audioconvert.c} or its corresponding integer representation
from the AV_CH_LAYOUT_* macros in @file{libavutil/audioconvert.h}

@item packing
Either "packed" or "planar", or their integer representation: 0 or 1
respectively.

@end table

For example:
@example
abuffer=44100:s16:stereo:planar
@end example

will instruct the source to accept planar 16bit signed stereo at 44100Hz.
Since the sample format with name "s16" corresponds to the number
1 and the "stereo" channel layout corresponds to the value 3, this is
equivalent to:
@example
abuffer=44100:1:3:1
@end example

@section aevalsrc

Generate an audio signal specified by an expression.

This source accepts in input one or more expressions (one for each
channel), which are evaluated and used to generate a corresponding
audio signal.

It accepts the syntax: @var{exprs}[::@var{options}].
@var{exprs} is a list of expressions separated by ":", one for each
separate channel. The output channel layout depends on the number of
provided expressions, up to 8 channels are supported.

@var{options} is an optional sequence of @var{key}=@var{value} pairs,
separated by ":".

The description of the accepted options follows.

@table @option

@item nb_samples, n
Set the number of samples per channel per each output frame,
default to 1024.

@item sample_rate, s
Specify the sample rate, default to 44100.
@end table

Each expression in @var{exprs} can contain the following constants:

@table @option
@item n
number of the evaluated sample, starting from 0

@item t
time of the evaluated sample expressed in seconds, starting from 0

@item s
sample rate

@end table

@subsection Examples

@itemize

@item
Generate silence:
@example
aevalsrc=0
@end example

@item

Generate a sin signal with frequence of 440 Hz, set sample rate to
8000 Hz:
@example
aevalsrc="sin(440*2*PI*t)::s=8000"
@end example

@item
Generate white noise:
@example
aevalsrc="-2+random(0)"
@end example

@item
Generate an amplitude modulated signal:
@example
aevalsrc="sin(10*2*PI*t)*sin(880*2*PI*t)"
@end example

@item
Generate 2.5 Hz binaural beats on a 360 Hz carrier:
@example
aevalsrc="0.1*sin(2*PI*(360-2.5/2)*t) : 0.1*sin(2*PI*(360+2.5/2)*t)"
@end example

@end itemize

@section amovie

Read an audio stream from a movie container.

It accepts the syntax: @var{movie_name}[:@var{options}] where
@var{movie_name} is the name of the resource to read (not necessarily
a file but also a device or a stream accessed through some protocol),
and @var{options} is an optional sequence of @var{key}=@var{value}
pairs, separated by ":".

The description of the accepted options follows.

@table @option

@item format_name, f
Specify the format assumed for the movie to read, and can be either
the name of a container or an input device. If not specified the
format is guessed from @var{movie_name} or by probing.

@item seek_point, sp
Specify the seek point in seconds, the frames will be output
starting from this seek point, the parameter is evaluated with
@code{av_strtod} so the numerical value may be suffixed by an IS
postfix. Default value is "0".

@item stream_index, si
Specify the index of the audio stream to read. If the value is -1,
the best suited audio stream will be automatically selected. Default
value is "-1".

@end table

@section anullsrc

Null audio source, return unprocessed audio frames. It is mainly useful
as a template and to be employed in analysis / debugging tools, or as
the source for filters which ignore the input data (for example the sox
synth filter).

It accepts an optional sequence of @var{key}=@var{value} pairs,
separated by ":".

The description of the accepted options follows.

@table @option

@item sample_rate, s
Specify the sample rate, and defaults to 44100.

@item channel_layout, cl

Specify the channel layout, and can be either an integer or a string
representing a channel layout. The default value of @var{channel_layout}
is "stereo".

Check the channel_layout_map definition in
@file{libavcodec/audioconvert.c} for the mapping between strings and
channel layout values.

@item nb_samples, n
Set the number of samples per requested frames.

@end table

Follow some examples:
@example
#  set the sample rate to 48000 Hz and the channel layout to AV_CH_LAYOUT_MONO.
anullsrc=r=48000:cl=4

# same as
anullsrc=r=48000:cl=mono
@end example

@c man end AUDIO SOURCES

@chapter Audio Sinks
@c man begin AUDIO SINKS

Below is a description of the currently available audio sinks.

@section abuffersink

Buffer audio frames, and make them available to the end of filter chain.

This sink is mainly intended for programmatic use, in particular
through the interface defined in @file{libavfilter/buffersink.h}.

It requires a pointer to an AVABufferSinkContext structure, which
defines the incoming buffers' formats, to be passed as the opaque
parameter to @code{avfilter_init_filter} for initialization.

@section anullsink

Null audio sink, do absolutely nothing with the input audio. It is
mainly useful as a template and to be employed in analysis / debugging
tools.

@c man end AUDIO SINKS

@chapter Video Filters
@c man begin VIDEO FILTERS

When you configure your FFmpeg build, you can disable any of the
existing filters using --disable-filters.
The configure output will show the video filters included in your
build.

Below is a description of the currently available video filters.

@section blackframe

Detect frames that are (almost) completely black. Can be useful to
detect chapter transitions or commercials. Output lines consist of
the frame number of the detected frame, the percentage of blackness,
the position in the file if known or -1 and the timestamp in seconds.

In order to display the output lines, you need to set the loglevel at
least to the AV_LOG_INFO value.

The filter accepts the syntax:
@example
blackframe[=@var{amount}:[@var{threshold}]]
@end example

@var{amount} is the percentage of the pixels that have to be below the
threshold, and defaults to 98.

@var{threshold} is the threshold below which a pixel value is
considered black, and defaults to 32.

@section boxblur

Apply boxblur algorithm to the input video.

This filter accepts the parameters:
@var{luma_radius}:@var{luma_power}:@var{chroma_radius}:@var{chroma_power}:@var{alpha_radius}:@var{alpha_power}

Chroma and alpha parameters are optional, if not specified they default
to the corresponding values set for @var{luma_radius} and
@var{luma_power}.

@var{luma_radius}, @var{chroma_radius}, and @var{alpha_radius} represent
the radius in pixels of the box used for blurring the corresponding
input plane. They are expressions, and can contain the following
constants:
@table @option
@item w, h
the input width and heigth in pixels

@item cw, ch
the input chroma image width and height in pixels

@item hsub, vsub
horizontal and vertical chroma subsample values. For example for the
pixel format "yuv422p" @var{hsub} is 2 and @var{vsub} is 1.
@end table

The radius must be a non-negative number, and must not be greater than
the value of the expression @code{min(w,h)/2} for the luma and alpha planes,
and of @code{min(cw,ch)/2} for the chroma planes.

@var{luma_power}, @var{chroma_power}, and @var{alpha_power} represent
how many times the boxblur filter is applied to the corresponding
plane.

Some examples follow:

@itemize

@item
Apply a boxblur filter with luma, chroma, and alpha radius
set to 2:
@example
boxblur=2:1
@end example

@item
Set luma radius to 2, alpha and chroma radius to 0
@example
boxblur=2:1:0:0:0:0
@end example

@item
Set luma and chroma radius to a fraction of the video dimension
@example
boxblur=min(h\,w)/10:1:min(cw\,ch)/10:1
@end example

@end itemize

@section copy

Copy the input source unchanged to the output. Mainly useful for
testing purposes.

@section crop

Crop the input video to @var{out_w}:@var{out_h}:@var{x}:@var{y}.

The parameters are expressions containing the following constants:

@table @option
@item x, y
the computed values for @var{x} and @var{y}. They are evaluated for
each new frame.

@item in_w, in_h
the input width and height

@item iw, ih
same as @var{in_w} and @var{in_h}

@item out_w, out_h
the output (cropped) width and height

@item ow, oh
same as @var{out_w} and @var{out_h}

@item a
same as @var{iw} / @var{ih}

@item sar
input sample aspect ratio

@item dar
input display aspect ratio, it is the same as (@var{iw} / @var{ih}) * @var{sar}

@item hsub, vsub
horizontal and vertical chroma subsample values. For example for the
pixel format "yuv422p" @var{hsub} is 2 and @var{vsub} is 1.

@item n
the number of input frame, starting from 0

@item pos
the position in the file of the input frame, NAN if unknown

@item t
timestamp expressed in seconds, NAN if the input timestamp is unknown

@end table

The @var{out_w} and @var{out_h} parameters specify the expressions for
the width and height of the output (cropped) video. They are
evaluated just at the configuration of the filter.

The default value of @var{out_w} is "in_w", and the default value of
@var{out_h} is "in_h".

The expression for @var{out_w} may depend on the value of @var{out_h},
and the expression for @var{out_h} may depend on @var{out_w}, but they
cannot depend on @var{x} and @var{y}, as @var{x} and @var{y} are
evaluated after @var{out_w} and @var{out_h}.

The @var{x} and @var{y} parameters specify the expressions for the
position of the top-left corner of the output (non-cropped) area. They
are evaluated for each frame. If the evaluated value is not valid, it
is approximated to the nearest valid value.

The default value of @var{x} is "(in_w-out_w)/2", and the default
value for @var{y} is "(in_h-out_h)/2", which set the cropped area at
the center of the input image.

The expression for @var{x} may depend on @var{y}, and the expression
for @var{y} may depend on @var{x}.

Follow some examples:
@example
# crop the central input area with size 100x100
crop=100:100

# crop the central input area with size 2/3 of the input video
"crop=2/3*in_w:2/3*in_h"

# crop the input video central square
crop=in_h

# delimit the rectangle with the top-left corner placed at position
# 100:100 and the right-bottom corner corresponding to the right-bottom
# corner of the input image.
crop=in_w-100:in_h-100:100:100

# crop 10 pixels from the left and right borders, and 20 pixels from
# the top and bottom borders
"crop=in_w-2*10:in_h-2*20"

# keep only the bottom right quarter of the input image
"crop=in_w/2:in_h/2:in_w/2:in_h/2"

# crop height for getting Greek harmony
"crop=in_w:1/PHI*in_w"

# trembling effect
"crop=in_w/2:in_h/2:(in_w-out_w)/2+((in_w-out_w)/2)*sin(n/10):(in_h-out_h)/2 +((in_h-out_h)/2)*sin(n/7)"

# erratic camera effect depending on timestamp
"crop=in_w/2:in_h/2:(in_w-out_w)/2+((in_w-out_w)/2)*sin(t*10):(in_h-out_h)/2 +((in_h-out_h)/2)*sin(t*13)"

# set x depending on the value of y
"crop=in_w/2:in_h/2:y:10+10*sin(n/10)"
@end example

@section cropdetect

Auto-detect crop size.

Calculate necessary cropping parameters and prints the recommended
parameters through the logging system. The detected dimensions
correspond to the non-black area of the input video.

It accepts the syntax:
@example
cropdetect[=@var{limit}[:@var{round}[:@var{reset}]]]
@end example

@table @option

@item limit
Threshold, which can be optionally specified from nothing (0) to
everything (255), defaults to 24.

@item round
Value which the width/height should be divisible by, defaults to
16. The offset is automatically adjusted to center the video. Use 2 to
get only even dimensions (needed for 4:2:2 video). 16 is best when
encoding to most video codecs.

@item reset
Counter that determines after how many frames cropdetect will reset
the previously detected largest video area and start over to detect
the current optimal crop area. Defaults to 0.

This can be useful when channel logos distort the video area. 0
indicates never reset and return the largest area encountered during
playback.
@end table

@section delogo

Suppress a TV station logo by a simple interpolation of the surrounding
pixels. Just set a rectangle covering the logo and watch it disappear
(and sometimes something even uglier appear - your mileage may vary).

The filter accepts parameters as a string of the form
"@var{x}:@var{y}:@var{w}:@var{h}:@var{band}", or as a list of
@var{key}=@var{value} pairs, separated by ":".

The description of the accepted parameters follows.

@table @option

@item x, y
Specify the top left corner coordinates of the logo. They must be
specified.

@item w, h
Specify the width and height of the logo to clear. They must be
specified.

@item band, t
Specify the thickness of the fuzzy edge of the rectangle (added to
@var{w} and @var{h}). The default value is 4.

@item show
When set to 1, a green rectangle is drawn on the screen to simplify
finding the right @var{x}, @var{y}, @var{w}, @var{h} parameters, and
@var{band} is set to 4. The default value is 0.

@end table

Some examples follow.

@itemize

@item
Set a rectangle covering the area with top left corner coordinates 0,0
and size 100x77, setting a band of size 10:
@example
delogo=0:0:100:77:10
@end example

@item
As the previous example, but use named options:
@example
delogo=x=0:y=0:w=100:h=77:band=10
@end example

@end itemize

@section deshake

Attempt to fix small changes in horizontal and/or vertical shift. This
filter helps remove camera shake from hand-holding a camera, bumping a
tripod, moving on a vehicle, etc.

The filter accepts parameters as a string of the form
"@var{x}:@var{y}:@var{w}:@var{h}:@var{rx}:@var{ry}:@var{edge}:@var{blocksize}:@var{contrast}:@var{search}:@var{filename}"

A description of the accepted parameters follows.

@table @option

@item x, y, w, h
Specify a rectangular area where to limit the sarch for motion
vectors.
If desired the search for motion vectors can be limited to a
rectangular area of the frame defined by its top left corner, width
and height. These parameters have the same meaning as the drawbox
filter which can be used to visualise the position of the bounding
box.

This is useful when simultaneous movement of subjects within the frame
might be confused for camera motion by the motion vector search.

If any or all of @var{x}, @var{y}, @var{w} and @var{h} are set to -1
then the full frame is used. This allows later options to be set
without specifying the bounding box for the motion vector search.

Default - search the whole frame.

@item rx, ry
Specify the maximum extent of movement in x and y directions in the
range 0-64 pixels. Default 16.

@item edge
Specify how to generate pixels to fill blanks at the edge of the
frame. An integer from 0 to 3 as follows:
@table @option
@item 0
Fill zeroes at blank locations
@item 1
Original image at blank locations
@item 2
Extruded edge value at blank locations
@item 3
Mirrored edge at blank locations
@end table

The default setting is mirror edge at blank locations.

@item blocksize
Specify the blocksize to use for motion search. Range 4-128 pixels,
default 8.

@item contrast
Specify the contrast threshold for blocks. Only blocks with more than
the specified contrast (difference between darkest and lightest
pixels) will be considered. Range 1-255, default 125.

@item search
Specify the search strategy 0 = exhaustive search, 1 = less exhaustive
search. Default - exhaustive search.

@item filename
If set then a detailed log of the motion search is written to the
specified file.

@end table

@section drawbox

Draw a colored box on the input image.

It accepts the syntax:
@example
drawbox=@var{x}:@var{y}:@var{width}:@var{height}:@var{color}
@end example

@table @option

@item x, y
Specify the top left corner coordinates of the box. Default to 0.

@item width, height
Specify the width and height of the box, if 0 they are interpreted as
the input width and height. Default to 0.

@item color
Specify the color of the box to write, it can be the name of a color
(case insensitive match) or a 0xRRGGBB[AA] sequence.
@end table

Follow some examples:
@example
# draw a black box around the edge of the input image
drawbox

# draw a box with color red and an opacity of 50%
drawbox=10:20:200:60:red@@0.5"
@end example

@section drawtext

Draw text string or text from specified file on top of video using the
libfreetype library.

To enable compilation of this filter you need to configure FFmpeg with
@code{--enable-libfreetype}.

The filter also recognizes strftime() sequences in the provided text
and expands them accordingly. Check the documentation of strftime().

The filter accepts parameters as a list of @var{key}=@var{value} pairs,
separated by ":".

The description of the accepted parameters follows.

@table @option

@item fontfile
The font file to be used for drawing text. Path must be included.
This parameter is mandatory.

@item text
The text string to be drawn. The text must be a sequence of UTF-8
encoded characters.
This parameter is mandatory if no file is specified with the parameter
@var{textfile}.

@item textfile
A text file containing text to be drawn. The text must be a sequence
of UTF-8 encoded characters.

This parameter is mandatory if no text string is specified with the
parameter @var{text}.

If both text and textfile are specified, an error is thrown.

@item x, y
The expressions which specify the offsets where text will be drawn
within the video frame. They are relative to the top/left border of the
output image.

The default value of @var{x} and @var{y} is "0".

See below for the list of accepted constants.

@item fontsize
The font size to be used for drawing text.
The default value of @var{fontsize} is 16.

@item fontcolor
The color to be used for drawing fonts.
Either a string (e.g. "red") or in 0xRRGGBB[AA] format
(e.g. "0xff000033"), possibly followed by an alpha specifier.
The default value of @var{fontcolor} is "black".

@item boxcolor
The color to be used for drawing box around text.
Either a string (e.g. "yellow") or in 0xRRGGBB[AA] format
(e.g. "0xff00ff"), possibly followed by an alpha specifier.
The default value of @var{boxcolor} is "white".

@item box
Used to draw a box around text using background color.
Value should be either 1 (enable) or 0 (disable).
The default value of @var{box} is 0.

@item shadowx, shadowy
The x and y offsets for the text shadow position with respect to the
position of the text. They can be either positive or negative
values. Default value for both is "0".

@item shadowcolor
The color to be used for drawing a shadow behind the drawn text.  It
can be a color name (e.g. "yellow") or a string in the 0xRRGGBB[AA]
form (e.g. "0xff00ff"), possibly followed by an alpha specifier.
The default value of @var{shadowcolor} is "black".

@item ft_load_flags
Flags to be used for loading the fonts.

The flags map the corresponding flags supported by libfreetype, and are
a combination of the following values:
@table @var
@item default
@item no_scale
@item no_hinting
@item render
@item no_bitmap
@item vertical_layout
@item force_autohint
@item crop_bitmap
@item pedantic
@item ignore_global_advance_width
@item no_recurse
@item ignore_transform
@item monochrome
@item linear_design
@item no_autohint
@item end table
@end table

Default value is "render".

For more information consult the documentation for the FT_LOAD_*
libfreetype flags.

@item tabsize
The size in number of spaces to use for rendering the tab.
Default value is 4.
@end table

The parameters for @var{x} and @var{y} are expressions containing the
following constants:

@table @option
@item w, h
the input width and heigth

@item tw, text_w
the width of the rendered text

@item th, text_h
the height of the rendered text

@item lh, line_h
the height of each text line

@item sar
input sample aspect ratio

@item dar
input display aspect ratio, it is the same as (@var{w} / @var{h}) * @var{sar}

@item hsub, vsub
horizontal and vertical chroma subsample values. For example for the
pixel format "yuv422p" @var{hsub} is 2 and @var{vsub} is 1.

@item max_glyph_w
maximum glyph width, that is the maximum width for all the glyphs
contained in the rendered text

@item max_glyph_h
maximum glyph height, that is the maximum height for all the glyphs
contained in the rendered text, it is equivalent to @var{ascent} -
@var{descent}.

@item max_glyph_a, ascent

the maximum distance from the baseline to the highest/upper grid
coordinate used to place a glyph outline point, for all the rendered
glyphs.
It is a positive value, due to the grid's orientation with the Y axis
upwards.

@item max_glyph_d, descent
the maximum distance from the baseline to the lowest grid coordinate
used to place a glyph outline point, for all the rendered glyphs.
This is a negative value, due to the grid's orientation, with the Y axis
upwards.

@item n
the number of input frame, starting from 0

@item t
timestamp expressed in seconds, NAN if the input timestamp is unknown
@end table

Some examples follow.

@itemize

@item
Draw "Test Text" with font FreeSerif, using the default values for the
optional parameters.

@example
drawtext="fontfile=/usr/share/fonts/truetype/freefont/FreeSerif.ttf: text='Test Text'"
@end example

@item
Draw 'Test Text' with font FreeSerif of size 24 at position x=100
and y=50 (counting from the top-left corner of the screen), text is
yellow with a red box around it. Both the text and the box have an
opacity of 20%.

@example
drawtext="fontfile=/usr/share/fonts/truetype/freefont/FreeSerif.ttf: text='Test Text':\
          x=100: y=50: fontsize=24: fontcolor=yellow@@0.2: box=1: boxcolor=red@@0.2"
@end example

Note that the double quotes are not necessary if spaces are not used
within the parameter list.

@item
Show the text at the center of the video frame:
@example
drawtext=fontsize=30:fontfile=FreeSerif.ttf:text='hello world':x=(w-text_w)/2:y=(h-text_h-line_h)/2"
@end example

@item
Show a text line sliding from right to left in the last row of the video
frame. The file @file{LONG_LINE} is assumed to contain a single line
with no newlines.
@example
drawtext=fontsize=15:fontfile=FreeSerif.ttf:text=LONG_LINE:y=h-line_h:x=-50*t
@end example

@item
Show the content of file @file{CREDITS} off the bottom of the frame and scroll up.
@example
drawtext=fontsize=20:fontfile=FreeSerif.ttf:textfile=CREDITS:y=h-20*t"
@end example

@item
Draw a single green letter "g", at the center of the input video.
The glyph baseline is placed at half screen height.
@example
drawtext=fontsize=60:fontfile=FreeSerif.ttf:fontcolor=green:text=g:x=(w-max_glyph_w)/2:y=h/2-ascent
@end example

@end itemize

For more information about libfreetype, check:
@url{http://www.freetype.org/}.

@section fade

Apply fade-in/out effect to input video.

It accepts the parameters:
@var{type}:@var{start_frame}:@var{nb_frames}

@var{type} specifies if the effect type, can be either "in" for
fade-in, or "out" for a fade-out effect.

@var{start_frame} specifies the number of the start frame for starting
to apply the fade effect.

@var{nb_frames} specifies the number of frames for which the fade
effect has to last. At the end of the fade-in effect the output video
will have the same intensity as the input video, at the end of the
fade-out transition the output video will be completely black.

A few usage examples follow, usable too as test scenarios.
@example
# fade in first 30 frames of video
fade=in:0:30

# fade out last 45 frames of a 200-frame video
fade=out:155:45

# fade in first 25 frames and fade out last 25 frames of a 1000-frame video
fade=in:0:25, fade=out:975:25

# make first 5 frames black, then fade in from frame 5-24
fade=in:5:20
@end example

@section fieldorder

Transform the field order of the input video.

It accepts one parameter which specifies the required field order that
the input interlaced video will be transformed to. The parameter can
assume one of the following values:

@table @option
@item 0 or bff
output bottom field first
@item 1 or tff
output top field first
@end table

Default value is "tff".

Transformation is achieved by shifting the picture content up or down
by one line, and filling the remaining line with appropriate picture content.
This method is consistent with most broadcast field order converters.

If the input video is not flagged as being interlaced, or it is already
flagged as being of the required output field order then this filter does
not alter the incoming video.

This filter is very useful when converting to or from PAL DV material,
which is bottom field first.

For example:
@example
./ffmpeg -i in.vob -vf "fieldorder=bff" out.dv
@end example

@section fifo

Buffer input images and send them when they are requested.

This filter is mainly useful when auto-inserted by the libavfilter
framework.

The filter does not take parameters.

@section format

Convert the input video to one of the specified pixel formats.
Libavfilter will try to pick one that is supported for the input to
the next filter.

The filter accepts a list of pixel format names, separated by ":",
for example "yuv420p:monow:rgb24".

Some examples follow:
@example
# convert the input video to the format "yuv420p"
format=yuv420p

# convert the input video to any of the formats in the list
format=yuv420p:yuv444p:yuv410p
@end example

@anchor{frei0r}
@section frei0r

Apply a frei0r effect to the input video.

To enable compilation of this filter you need to install the frei0r
header and configure FFmpeg with --enable-frei0r.

The filter supports the syntax:
@example
@var{filter_name}[@{:|=@}@var{param1}:@var{param2}:...:@var{paramN}]
@end example

@var{filter_name} is the name to the frei0r effect to load. If the
environment variable @env{FREI0R_PATH} is defined, the frei0r effect
is searched in each one of the directories specified by the colon
separated list in @env{FREIOR_PATH}, otherwise in the standard frei0r
paths, which are in this order: @file{HOME/.frei0r-1/lib/},
@file{/usr/local/lib/frei0r-1/}, @file{/usr/lib/frei0r-1/}.

@var{param1}, @var{param2}, ... , @var{paramN} specify the parameters
for the frei0r effect.

A frei0r effect parameter can be a boolean (whose values are specified
with "y" and "n"), a double, a color (specified by the syntax
@var{R}/@var{G}/@var{B}, @var{R}, @var{G}, and @var{B} being float
numbers from 0.0 to 1.0) or by an @code{av_parse_color()} color
description), a position (specified by the syntax @var{X}/@var{Y},
@var{X} and @var{Y} being float numbers) and a string.

The number and kind of parameters depend on the loaded effect. If an
effect parameter is not specified the default value is set.

Some examples follow:
@example
# apply the distort0r effect, set the first two double parameters
frei0r=distort0r:0.5:0.01

# apply the colordistance effect, takes a color as first parameter
frei0r=colordistance:0.2/0.3/0.4
frei0r=colordistance:violet
frei0r=colordistance:0x112233

# apply the perspective effect, specify the top left and top right
# image positions
frei0r=perspective:0.2/0.2:0.8/0.2
@end example

For more information see:
@url{http://piksel.org/frei0r}

@section gradfun

Fix the banding artifacts that are sometimes introduced into nearly flat
regions by truncation to 8bit colordepth.
Interpolate the gradients that should go where the bands are, and
dither them.

This filter is designed for playback only.  Do not use it prior to
lossy compression, because compression tends to lose the dither and
bring back the bands.

The filter takes two optional parameters, separated by ':':
@var{strength}:@var{radius}

@var{strength} is the maximum amount by which the filter will change
any one pixel. Also the threshold for detecting nearly flat
regions. Acceptable values range from .51 to 255, default value is
1.2, out-of-range values will be clipped to the valid range.

@var{radius} is the neighborhood to fit the gradient to. A larger
radius makes for smoother gradients, but also prevents the filter from
modifying the pixels near detailed regions. Acceptable values are
8-32, default value is 16, out-of-range values will be clipped to the
valid range.

@example
# default parameters
gradfun=1.2:16

# omitting radius
gradfun=1.2
@end example

@section hflip

Flip the input video horizontally.

For example to horizontally flip the video in input with
@file{ffmpeg}:
@example
ffmpeg -i in.avi -vf "hflip" out.avi
@end example

@section hqdn3d

High precision/quality 3d denoise filter. This filter aims to reduce
image noise producing smooth images and making still images really
still. It should enhance compressibility.

It accepts the following optional parameters:
@var{luma_spatial}:@var{chroma_spatial}:@var{luma_tmp}:@var{chroma_tmp}

@table @option
@item luma_spatial
a non-negative float number which specifies spatial luma strength,
defaults to 4.0

@item chroma_spatial
a non-negative float number which specifies spatial chroma strength,
defaults to 3.0*@var{luma_spatial}/4.0

@item luma_tmp
a float number which specifies luma temporal strength, defaults to
6.0*@var{luma_spatial}/4.0

@item chroma_tmp
a float number which specifies chroma temporal strength, defaults to
@var{luma_tmp}*@var{chroma_spatial}/@var{luma_spatial}
@end table

@section lut, lutrgb, lutyuv

Compute a look-up table for binding each pixel component input value
to an output value, and apply it to input video.

@var{lutyuv} applies a lookup table to a YUV input video, @var{lutrgb}
to an RGB input video.

These filters accept in input a ":"-separated list of options, which
specify the expressions used for computing the lookup table for the
corresponding pixel component values.

The @var{lut} filter requires either YUV or RGB pixel formats in
input, and accepts the options:
@table @option
@item c0
first  pixel component
@item c1
second pixel component
@item c2
third  pixel component
@item c3
fourth pixel component, corresponds to the alpha component
@end table

The exact component associated to each option depends on the format in
input.

The @var{lutrgb} filter requires RGB pixel formats in input, and
accepts the options:
@table @option
@item r
red component
@item g
green component
@item b
blue component
@item a
alpha component
@end table

The @var{lutyuv} filter requires YUV pixel formats in input, and
accepts the options:
@table @option
@item y
Y/luminance component
@item u
U/Cb component
@item v
V/Cr component
@item a
alpha component
@end table

The expressions can contain the following constants and functions:

@table @option
@item w, h
the input width and heigth

@item val
input value for the pixel component

@item clipval
the input value clipped in the @var{minval}-@var{maxval} range

@item maxval
maximum value for the pixel component

@item minval
minimum value for the pixel component

@item negval
the negated value for the pixel component value clipped in the
@var{minval}-@var{maxval} range , it corresponds to the expression
"maxval-clipval+minval"

@item clip(val)
the computed value in @var{val} clipped in the
@var{minval}-@var{maxval} range

@item gammaval(gamma)
the computed gamma correction value of the pixel component value
clipped in the @var{minval}-@var{maxval} range, corresponds to the
expression
"pow((clipval-minval)/(maxval-minval)\,@var{gamma})*(maxval-minval)+minval"

@end table

All expressions default to "val".

Some examples follow:
@example
# negate input video
lutrgb="r=maxval+minval-val:g=maxval+minval-val:b=maxval+minval-val"
lutyuv="y=maxval+minval-val:u=maxval+minval-val:v=maxval+minval-val"

# the above is the same as
lutrgb="r=negval:g=negval:b=negval"
lutyuv="y=negval:u=negval:v=negval"

# negate luminance
lutyuv=y=negval

# remove chroma components, turns the video into a graytone image
lutyuv="u=128:v=128"

# apply a luma burning effect
lutyuv="y=2*val"

# remove green and blue components
lutrgb="g=0:b=0"

# set a constant alpha channel value on input
format=rgba,lutrgb=a="maxval-minval/2"

# correct luminance gamma by a 0.5 factor
lutyuv=y=gammaval(0.5)
@end example

@section mp

Apply an MPlayer filter to the input video.

This filter provides a wrapper around most of the filters of
MPlayer/MEncoder.

This wrapper is considered experimental. Some of the wrapped filters
may not work properly and we may drop support for them, as they will
be implemented natively into FFmpeg. Thus you should avoid
depending on them when writing portable scripts.

The filters accepts the parameters:
@var{filter_name}[:=]@var{filter_params}

@var{filter_name} is the name of a supported MPlayer filter,
@var{filter_params} is a string containing the parameters accepted by
the named filter.

The list of the currently supported filters follows:
@table @var
@item 2xsai
@item decimate
@item denoise3d
@item detc
@item dint
@item divtc
@item down3dright
@item dsize
@item eq2
@item eq
@item field
@item fil
@item fixpts
@item framestep
@item fspp
@item geq
@item harddup
@item hqdn3d
@item hue
@item il
@item ilpack
@item ivtc
@item kerndeint
@item mcdeint
@item mirror
@item noise
@item ow
@item palette
@item perspective
@item phase
@item pp7
@item pullup
@item qp
@item rectangle
@item remove-logo
@item rotate
@item sab
@item screenshot
@item smartblur
@item softpulldown
@item softskip
@item spp
@item swapuv
@item telecine
@item tile
@item tinterlace
@item unsharp
@item uspp
@item yuvcsp
@item yvu9
@end table

The parameter syntax and behavior for the listed filters are the same
of the corresponding MPlayer filters. For detailed instructions check
the "VIDEO FILTERS" section in the MPlayer manual.

Some examples follow:
@example
# remove a logo by interpolating the surrounding pixels
mp=delogo=200:200:80:20:1

# adjust gamma, brightness, contrast
mp=eq2=1.0:2:0.5

# tweak hue and saturation
mp=hue=100:-10
@end example

See also mplayer(1), @url{http://www.mplayerhq.hu/}.

@section negate

Negate input video.

This filter accepts an integer in input, if non-zero it negates the
alpha component (if available). The default value in input is 0.

@section noformat

Force libavfilter not to use any of the specified pixel formats for the
input to the next filter.

The filter accepts a list of pixel format names, separated by ":",
for example "yuv420p:monow:rgb24".

Some examples follow:
@example
# force libavfilter to use a format different from "yuv420p" for the
# input to the vflip filter
noformat=yuv420p,vflip

# convert the input video to any of the formats not contained in the list
noformat=yuv420p:yuv444p:yuv410p
@end example

@section null

Pass the video source unchanged to the output.

@section ocv

Apply video transform using libopencv.

To enable this filter install libopencv library and headers and
configure FFmpeg with --enable-libopencv.

The filter takes the parameters: @var{filter_name}@{:=@}@var{filter_params}.

@var{filter_name} is the name of the libopencv filter to apply.

@var{filter_params} specifies the parameters to pass to the libopencv
filter. If not specified the default values are assumed.

Refer to the official libopencv documentation for more precise
informations:
@url{http://opencv.willowgarage.com/documentation/c/image_filtering.html}

Follows the list of supported libopencv filters.

@anchor{dilate}
@subsection dilate

Dilate an image by using a specific structuring element.
This filter corresponds to the libopencv function @code{cvDilate}.

It accepts the parameters: @var{struct_el}:@var{nb_iterations}.

@var{struct_el} represents a structuring element, and has the syntax:
@var{cols}x@var{rows}+@var{anchor_x}x@var{anchor_y}/@var{shape}

@var{cols} and @var{rows} represent the number of colums and rows of
the structuring element, @var{anchor_x} and @var{anchor_y} the anchor
point, and @var{shape} the shape for the structuring element, and
can be one of the values "rect", "cross", "ellipse", "custom".

If the value for @var{shape} is "custom", it must be followed by a
string of the form "=@var{filename}". The file with name
@var{filename} is assumed to represent a binary image, with each
printable character corresponding to a bright pixel. When a custom
@var{shape} is used, @var{cols} and @var{rows} are ignored, the number
or columns and rows of the read file are assumed instead.

The default value for @var{struct_el} is "3x3+0x0/rect".

@var{nb_iterations} specifies the number of times the transform is
applied to the image, and defaults to 1.

Follow some example:
@example
# use the default values
ocv=dilate

# dilate using a structuring element with a 5x5 cross, iterate two times
ocv=dilate=5x5+2x2/cross:2

# read the shape from the file diamond.shape, iterate two times
# the file diamond.shape may contain a pattern of characters like this:
#   *
#  ***
# *****
#  ***
#   *
# the specified cols and rows are ignored (but not the anchor point coordinates)
ocv=0x0+2x2/custom=diamond.shape:2
@end example

@subsection erode

Erode an image by using a specific structuring element.
This filter corresponds to the libopencv function @code{cvErode}.

The filter accepts the parameters: @var{struct_el}:@var{nb_iterations},
with the same syntax and semantics as the @ref{dilate} filter.

@subsection smooth

Smooth the input video.

The filter takes the following parameters:
@var{type}:@var{param1}:@var{param2}:@var{param3}:@var{param4}.

@var{type} is the type of smooth filter to apply, and can be one of
the following values: "blur", "blur_no_scale", "median", "gaussian",
"bilateral". The default value is "gaussian".

@var{param1}, @var{param2}, @var{param3}, and @var{param4} are
parameters whose meanings depend on smooth type. @var{param1} and
@var{param2} accept integer positive values or 0, @var{param3} and
@var{param4} accept float values.

The default value for @var{param1} is 3, the default value for the
other parameters is 0.

These parameters correspond to the parameters assigned to the
libopencv function @code{cvSmooth}.

@section overlay

Overlay one video on top of another.

It takes two inputs and one output, the first input is the "main"
video on which the second input is overlayed.

It accepts the parameters: @var{x}:@var{y}.

@var{x} is the x coordinate of the overlayed video on the main video,
@var{y} is the y coordinate. The parameters are expressions containing
the following parameters:

@table @option
@item main_w, main_h
main input width and height

@item W, H
same as @var{main_w} and @var{main_h}

@item overlay_w, overlay_h
overlay input width and height

@item w, h
same as @var{overlay_w} and @var{overlay_h}
@end table

Be aware that frames are taken from each input video in timestamp
order, hence, if their initial timestamps differ, it is a a good idea
to pass the two inputs through a @var{setpts=PTS-STARTPTS} filter to
have them begin in the same zero timestamp, as it does the example for
the @var{movie} filter.

Follow some examples:
@example
# draw the overlay at 10 pixels from the bottom right
# corner of the main video.
overlay=main_w-overlay_w-10:main_h-overlay_h-10

# insert a transparent PNG logo in the bottom left corner of the input
movie=logo.png [logo];
[in][logo] overlay=10:main_h-overlay_h-10 [out]

# insert 2 different transparent PNG logos (second logo on bottom
# right corner):
movie=logo1.png [logo1];
movie=logo2.png [logo2];
[in][logo1]       overlay=10:H-h-10 [in+logo1];
[in+logo1][logo2] overlay=W-w-10:H-h-10 [out]

# add a transparent color layer on top of the main video,
# WxH specifies the size of the main input to the overlay filter
color=red@.3:WxH [over]; [in][over] overlay [out]
@end example

You can chain togheter more overlays but the efficiency of such
approach is yet to be tested.

@section pad

Add paddings to the input image, and places the original input at the
given coordinates @var{x}, @var{y}.

It accepts the following parameters:
@var{width}:@var{height}:@var{x}:@var{y}:@var{color}.

The parameters @var{width}, @var{height}, @var{x}, and @var{y} are
expressions containing the following constants:

@table @option
@item in_w, in_h
the input video width and height

@item iw, ih
same as @var{in_w} and @var{in_h}

@item out_w, out_h
the output width and height, that is the size of the padded area as
specified by the @var{width} and @var{height} expressions

@item ow, oh
same as @var{out_w} and @var{out_h}

@item x, y
x and y offsets as specified by the @var{x} and @var{y}
expressions, or NAN if not yet specified

@item a
same as @var{iw} / @var{ih}

@item sar
input sample aspect ratio

@item dar
input display aspect ratio, it is the same as (@var{iw} / @var{ih}) * @var{sar}

@item hsub, vsub
horizontal and vertical chroma subsample values. For example for the
pixel format "yuv422p" @var{hsub} is 2 and @var{vsub} is 1.
@end table

Follows the description of the accepted parameters.

@table @option
@item width, height

Specify the size of the output image with the paddings added. If the
value for @var{width} or @var{height} is 0, the corresponding input size
is used for the output.

The @var{width} expression can reference the value set by the
@var{height} expression, and viceversa.

The default value of @var{width} and @var{height} is 0.

@item x, y

Specify the offsets where to place the input image in the padded area
with respect to the top/left border of the output image.

The @var{x} expression can reference the value set by the @var{y}
expression, and viceversa.

The default value of @var{x} and @var{y} is 0.

@item color

Specify the color of the padded area, it can be the name of a color
(case insensitive match) or a 0xRRGGBB[AA] sequence.

The default value of @var{color} is "black".

@end table

Some examples follow:

@example
# Add paddings with color "violet" to the input video. Output video
# size is 640x480, the top-left corner of the input video is placed at
# column 0, row 40.
pad=640:480:0:40:violet

# pad the input to get an output with dimensions increased bt 3/2,
# and put the input video at the center of the padded area
pad="3/2*iw:3/2*ih:(ow-iw)/2:(oh-ih)/2"

# pad the input to get a squared output with size equal to the maximum
# value between the input width and height, and put the input video at
# the center of the padded area
pad="max(iw\,ih):ow:(ow-iw)/2:(oh-ih)/2"

# pad the input to get a final w/h ratio of 16:9
pad="ih*16/9:ih:(ow-iw)/2:(oh-ih)/2"

# for anamorphic video, in order to set the output display aspect ratio,
# it is necessary to use sar in the expression, according to the relation:
# (ih * X / ih) * sar = output_dar
# X = output_dar / sar
pad="ih*16/9/sar:ih:(ow-iw)/2:(oh-ih)/2"

# double output size and put the input video in the bottom-right
# corner of the output padded area
pad="2*iw:2*ih:ow-iw:oh-ih"
@end example

@section pixdesctest

Pixel format descriptor test filter, mainly useful for internal
testing. The output video should be equal to the input video.

For example:
@example
format=monow, pixdesctest
@end example

can be used to test the monowhite pixel format descriptor definition.

@section scale

Scale the input video to @var{width}:@var{height}[:@var{interl}=@{1|-1@}] and/or convert the image format.

The parameters @var{width} and @var{height} are expressions containing
the following constants:

@table @option
@item in_w, in_h
the input width and height

@item iw, ih
same as @var{in_w} and @var{in_h}

@item out_w, out_h
the output (cropped) width and height

@item ow, oh
same as @var{out_w} and @var{out_h}

@item a
same as @var{iw} / @var{ih}

@item sar
input sample aspect ratio

@item dar
input display aspect ratio, it is the same as (@var{iw} / @var{ih}) * @var{sar}

@item sar
input sample aspect ratio

@item hsub, vsub
horizontal and vertical chroma subsample values. For example for the
pixel format "yuv422p" @var{hsub} is 2 and @var{vsub} is 1.
@end table

If the input image format is different from the format requested by
the next filter, the scale filter will convert the input to the
requested format.

If the value for @var{width} or @var{height} is 0, the respective input
size is used for the output.

If the value for @var{width} or @var{height} is -1, the scale filter will
use, for the respective output size, a value that maintains the aspect
ratio of the input image.

The default value of @var{width} and @var{height} is 0.

Valid values for the optional parameter @var{interl} are:

@table @option
@item 1
force interlaced aware scaling

@item -1
select interlaced aware scaling depending on whether the source frames
are flagged as interlaced or not
@end table

Some examples follow:
@example
# scale the input video to a size of 200x100.
scale=200:100

# scale the input to 2x
scale=2*iw:2*ih
# the above is the same as
scale=2*in_w:2*in_h

# scale the input to half size
scale=iw/2:ih/2

# increase the width, and set the height to the same size
scale=3/2*iw:ow

# seek for Greek harmony
scale=iw:1/PHI*iw
scale=ih*PHI:ih

# increase the height, and set the width to 3/2 of the height
scale=3/2*oh:3/5*ih

# increase the size, but make the size a multiple of the chroma
scale="trunc(3/2*iw/hsub)*hsub:trunc(3/2*ih/vsub)*vsub"

# increase the width to a maximum of 500 pixels, keep the same input aspect ratio
scale='min(500\, iw*3/2):-1'
@end example

@section select
Select frames to pass in output.

It accepts in input an expression, which is evaluated for each input
frame. If the expression is evaluated to a non-zero value, the frame
is selected and passed to the output, otherwise it is discarded.

The expression can contain the following constants:

@table @option
@item n
the sequential number of the filtered frame, starting from 0

@item selected_n
the sequential number of the selected frame, starting from 0

@item prev_selected_n
the sequential number of the last selected frame, NAN if undefined

@item TB
timebase of the input timestamps

@item pts
the PTS (Presentation TimeStamp) of the filtered video frame,
expressed in @var{TB} units, NAN if undefined

@item t
the PTS (Presentation TimeStamp) of the filtered video frame,
expressed in seconds, NAN if undefined

@item prev_pts
the PTS of the previously filtered video frame, NAN if undefined

@item prev_selected_pts
the PTS of the last previously filtered video frame, NAN if undefined

@item prev_selected_t
the PTS of the last previously selected video frame, NAN if undefined

@item start_pts
the PTS of the first video frame in the video, NAN if undefined

@item start_t
the time of the first video frame in the video, NAN if undefined

@item pict_type
the type of the filtered frame, can assume one of the following
values:
@table @option
@item I
@item P
@item B
@item S
@item SI
@item SP
@item BI
@end table

@item interlace_type
the frame interlace type, can assume one of the following values:
@table @option
@item PROGRESSIVE
the frame is progressive (not interlaced)
@item TOPFIRST
the frame is top-field-first
@item BOTTOMFIRST
the frame is bottom-field-first
@end table

@item key
1 if the filtered frame is a key-frame, 0 otherwise

@item pos
the position in the file of the filtered frame, -1 if the information
is not available (e.g. for synthetic video)
@end table

The default value of the select expression is "1".

Some examples follow:

@example
# select all frames in input
select

# the above is the same as:
select=1

# skip all frames:
select=0

# select only I-frames
select='eq(pict_type\,I)'

# select one frame every 100
select='not(mod(n\,100))'

# select only frames contained in the 10-20 time interval
select='gte(t\,10)*lte(t\,20)'

# select only I frames contained in the 10-20 time interval
select='gte(t\,10)*lte(t\,20)*eq(pict_type\,I)'

# select frames with a minimum distance of 10 seconds
select='isnan(prev_selected_t)+gte(t-prev_selected_t\,10)'
@end example

@anchor{setdar}
@section setdar

Set the Display Aspect Ratio for the filter output video.

This is done by changing the specified Sample (aka Pixel) Aspect
Ratio, according to the following equation:
@math{DAR = HORIZONTAL_RESOLUTION / VERTICAL_RESOLUTION * SAR}

Keep in mind that this filter does not modify the pixel dimensions of
the video frame. Also the display aspect ratio set by this filter may
be changed by later filters in the filterchain, e.g. in case of
scaling or if another "setdar" or a "setsar" filter is applied.

The filter accepts a parameter string which represents the wanted
display aspect ratio.
The parameter can be a floating point number string, or an expression
of the form @var{num}:@var{den}, where @var{num} and @var{den} are the
numerator and denominator of the aspect ratio.
If the parameter is not specified, it is assumed the value "0:1".

For example to change the display aspect ratio to 16:9, specify:
@example
setdar=16:9
# the above is equivalent to
setdar=1.77777
@end example

See also the @ref{setsar} filter documentation.

@section setpts

Change the PTS (presentation timestamp) of the input video frames.

Accept in input an expression evaluated through the eval API, which
can contain the following constants:

@table @option
@item PTS
the presentation timestamp in input

@item N
the count of the input frame, starting from 0.

@item STARTPTS
the PTS of the first video frame

@item INTERLACED
tell if the current frame is interlaced

@item POS
original position in the file of the frame, or undefined if undefined
for the current frame

@item PREV_INPTS
previous input PTS

@item PREV_OUTPTS
previous output PTS

@end table

Some examples follow:

@example
# start counting PTS from zero
setpts=PTS-STARTPTS

# fast motion
setpts=0.5*PTS

# slow motion
setpts=2.0*PTS

# fixed rate 25 fps
setpts=N/(25*TB)

# fixed rate 25 fps with some jitter
setpts='1/(25*TB) * (N + 0.05 * sin(N*2*PI/25))'
@end example

@anchor{setsar}
@section setsar

Set the Sample (aka Pixel) Aspect Ratio for the filter output video.

Note that as a consequence of the application of this filter, the
output display aspect ratio will change according to the following
equation:
@math{DAR = HORIZONTAL_RESOLUTION / VERTICAL_RESOLUTION * SAR}

Keep in mind that the sample aspect ratio set by this filter may be
changed by later filters in the filterchain, e.g. if another "setsar"
or a "setdar" filter is applied.

The filter accepts a parameter string which represents the wanted
sample aspect ratio.
The parameter can be a floating point number string, or an expression
of the form @var{num}:@var{den}, where @var{num} and @var{den} are the
numerator and denominator of the aspect ratio.
If the parameter is not specified, it is assumed the value "0:1".

For example to change the sample aspect ratio to 10:11, specify:
@example
setsar=10:11
@end example

@section settb

Set the timebase to use for the output frames timestamps.
It is mainly useful for testing timebase configuration.

It accepts in input an arithmetic expression representing a rational.
The expression can contain the constants "AVTB" (the
default timebase), and "intb" (the input timebase).

The default value for the input is "intb".

Follow some examples.

@example
# set the timebase to 1/25
settb=1/25

# set the timebase to 1/10
settb=0.1

#set the timebase to 1001/1000
settb=1+0.001

#set the timebase to 2*intb
settb=2*intb

#set the default timebase value
settb=AVTB
@end example

@section showinfo

Show a line containing various information for each input video frame.
The input video is not modified.

The shown line contains a sequence of key/value pairs of the form
@var{key}:@var{value}.

A description of each shown parameter follows:

@table @option
@item n
sequential number of the input frame, starting from 0

@item pts
Presentation TimeStamp of the input frame, expressed as a number of
time base units. The time base unit depends on the filter input pad.

@item pts_time
Presentation TimeStamp of the input frame, expressed as a number of
seconds

@item pos
position of the frame in the input stream, -1 if this information in
unavailable and/or meanigless (for example in case of synthetic video)

@item fmt
pixel format name

@item sar
sample aspect ratio of the input frame, expressed in the form
@var{num}/@var{den}

@item s
size of the input frame, expressed in the form
@var{width}x@var{height}

@item i
interlaced mode ("P" for "progressive", "T" for top field first, "B"
for bottom field first)

@item iskey
1 if the frame is a key frame, 0 otherwise

@item type
picture type of the input frame ("I" for an I-frame, "P" for a
P-frame, "B" for a B-frame, "?" for unknown type).
Check also the documentation of the @code{AVPictureType} enum and of
the @code{av_get_picture_type_char} function defined in
@file{libavutil/avutil.h}.

@item checksum
Adler-32 checksum (printed in hexadecimal) of all the planes of the input frame

@item plane_checksum
Adler-32 checksum (printed in hexadecimal) of each plane of the input frame,
expressed in the form "[@var{c0} @var{c1} @var{c2} @var{c3}]"
@end table

@section slicify

Pass the images of input video on to next video filter as multiple
slices.

@example
./ffmpeg -i in.avi -vf "slicify=32" out.avi
@end example

The filter accepts the slice height as parameter. If the parameter is
not specified it will use the default value of 16.

Adding this in the beginning of filter chains should make filtering
faster due to better use of the memory cache.

@section split

Pass on the input video to two outputs. Both outputs are identical to
the input video.

For example:
@example
[in] split [splitout1][splitout2];
[splitout1] crop=100:100:0:0    [cropout];
[splitout2] pad=200:200:100:100 [padout];
@end example

will create two separate outputs from the same input, one cropped and
one padded.

@section transpose

Transpose rows with columns in the input video and optionally flip it.

It accepts a parameter representing an integer, which can assume the
values:

@table @samp
@item 0
Rotate by 90 degrees counterclockwise and vertically flip (default), that is:
@example
L.R     L.l
. . ->  . .
l.r     R.r
@end example

@item 1
Rotate by 90 degrees clockwise, that is:
@example
L.R     l.L
. . ->  . .
l.r     r.R
@end example

@item 2
Rotate by 90 degrees counterclockwise, that is:
@example
L.R     R.r
. . ->  . .
l.r     L.l
@end example

@item 3
Rotate by 90 degrees clockwise and vertically flip, that is:
@example
L.R     r.R
. . ->  . .
l.r     l.L
@end example
@end table

@section unsharp

Sharpen or blur the input video.

It accepts the following parameters:
@var{luma_msize_x}:@var{luma_msize_y}:@var{luma_amount}:@var{chroma_msize_x}:@var{chroma_msize_y}:@var{chroma_amount}

Negative values for the amount will blur the input video, while positive
values will sharpen. All parameters are optional and default to the
equivalent of the string '5:5:1.0:5:5:0.0'.

@table @option

@item luma_msize_x
Set the luma matrix horizontal size. It can be an integer between 3
and 13, default value is 5.

@item luma_msize_y
Set the luma matrix vertical size. It can be an integer between 3
and 13, default value is 5.

@item luma_amount
Set the luma effect strength. It can be a float number between -2.0
and 5.0, default value is 1.0.

@item chroma_msize_x
Set the chroma matrix horizontal size. It can be an integer between 3
and 13, default value is 5.

@item chroma_msize_y
Set the chroma matrix vertical size. It can be an integer between 3
and 13, default value is 5.

@item chroma_amount
Set the chroma effect strength. It can be a float number between -2.0
and 5.0, default value is 0.0.

@end table

@example
# Strong luma sharpen effect parameters
unsharp=7:7:2.5

# Strong blur of both luma and chroma parameters
unsharp=7:7:-2:7:7:-2

# Use the default values with @command{ffmpeg}
./ffmpeg -i in.avi -vf "unsharp" out.mp4
@end example

@section vflip

Flip the input video vertically.

@example
./ffmpeg -i in.avi -vf "vflip" out.avi
@end example

@section yadif

Deinterlace the input video ("yadif" means "yet another deinterlacing
filter").

It accepts the optional parameters: @var{mode}:@var{parity}:@var{auto}.

@var{mode} specifies the interlacing mode to adopt, accepts one of the
following values:

@table @option
@item 0
output 1 frame for each frame
@item 1
output 1 frame for each field
@item 2
like 0 but skips spatial interlacing check
@item 3
like 1 but skips spatial interlacing check
@end table

Default value is 0.

@var{parity} specifies the picture field parity assumed for the input
interlaced video, accepts one of the following values:

@table @option
@item 0
assume top field first
@item 1
assume bottom field first
@item -1
enable automatic detection
@end table

Default value is -1.
If interlacing is unknown or decoder does not export this information,
top field first will be assumed.

@var{auto} specifies if deinterlacer should trust the interlaced flag
and only deinterlace frames marked as interlaced

@table @option
@item 0
deinterlace all frames
@item 1
only deinterlace frames marked as interlaced
@end table

Default value is 0.

@c man end VIDEO FILTERS

@chapter Video Sources
@c man begin VIDEO SOURCES

Below is a description of the currently available video sources.

@section buffer

Buffer video frames, and make them available to the filter chain.

This source is mainly intended for a programmatic use, in particular
through the interface defined in @file{libavfilter/vsrc_buffer.h}.

It accepts the following parameters:
@var{width}:@var{height}:@var{pix_fmt_string}:@var{timebase_num}:@var{timebase_den}:@var{sample_aspect_ratio_num}:@var{sample_aspect_ratio.den}:@var{scale_params}

All the parameters but @var{scale_params} need to be explicitely
defined.

Follows the list of the accepted parameters.

@table @option

@item width, height
Specify the width and height of the buffered video frames.

@item pix_fmt_string
A string representing the pixel format of the buffered video frames.
It may be a number corresponding to a pixel format, or a pixel format
name.

@item timebase_num, timebase_den
Specify numerator and denomitor of the timebase assumed by the
timestamps of the buffered frames.

@item sample_aspect_ratio.num, sample_aspect_ratio.den
Specify numerator and denominator of the sample aspect ratio assumed
by the video frames.

@item scale_params
Specify the optional parameters to be used for the scale filter which
is automatically inserted when an input change is detected in the
input size or format.
@end table

For example:
@example
buffer=320:240:yuv410p:1:24:1:1
@end example

will instruct the source to accept video frames with size 320x240 and
with format "yuv410p", assuming 1/24 as the timestamps timebase and
square pixels (1:1 sample aspect ratio).
Since the pixel format with name "yuv410p" corresponds to the number 6
(check the enum PixelFormat definition in @file{libavutil/pixfmt.h}),
this example corresponds to:
@example
buffer=320:240:6:1:24:1:1
@end example

@section color

Provide an uniformly colored input.

It accepts the following parameters:
@var{color}:@var{frame_size}:@var{frame_rate}

Follows the description of the accepted parameters.

@table @option

@item color
Specify the color of the source. It can be the name of a color (case
insensitive match) or a 0xRRGGBB[AA] sequence, possibly followed by an
alpha specifier. The default value is "black".

@item frame_size
Specify the size of the sourced video, it may be a string of the form
@var{width}x@var{height}, or the name of a size abbreviation. The
default value is "320x240".

@item frame_rate
Specify the frame rate of the sourced video, as the number of frames
generated per second. It has to be a string in the format
@var{frame_rate_num}/@var{frame_rate_den}, an integer number, a float
number or a valid video frame rate abbreviation. The default value is
"25".

@end table

For example the following graph description will generate a red source
with an opacity of 0.2, with size "qcif" and a frame rate of 10
frames per second, which will be overlayed over the source connected
to the pad with identifier "in".

@example
"color=red@@0.2:qcif:10 [color]; [in][color] overlay [out]"
@end example

@section movie

Read a video stream from a movie container.

It accepts the syntax: @var{movie_name}[:@var{options}] where
@var{movie_name} is the name of the resource to read (not necessarily
a file but also a device or a stream accessed through some protocol),
and @var{options} is an optional sequence of @var{key}=@var{value}
pairs, separated by ":".

The description of the accepted options follows.

@table @option

@item format_name, f
Specifies the format assumed for the movie to read, and can be either
the name of a container or an input device. If not specified the
format is guessed from @var{movie_name} or by probing.

@item seek_point, sp
Specifies the seek point in seconds, the frames will be output
starting from this seek point, the parameter is evaluated with
@code{av_strtod} so the numerical value may be suffixed by an IS
postfix. Default value is "0".

@item stream_index, si
Specifies the index of the video stream to read. If the value is -1,
the best suited video stream will be automatically selected. Default
value is "-1".

@end table

This filter allows to overlay a second video on top of main input of
a filtergraph as shown in this graph:
@example
input -----------> deltapts0 --> overlay --> output
                                    ^
                                    |
movie --> scale--> deltapts1 -------+
@end example

Some examples follow:
@example
# skip 3.2 seconds from the start of the avi file in.avi, and overlay it
# on top of the input labelled as "in".
movie=in.avi:seek_point=3.2, scale=180:-1, setpts=PTS-STARTPTS [movie];
[in] setpts=PTS-STARTPTS, [movie] overlay=16:16 [out]

# read from a video4linux2 device, and overlay it on top of the input
# labelled as "in"
movie=/dev/video0:f=video4linux2, scale=180:-1, setpts=PTS-STARTPTS [movie];
[in] setpts=PTS-STARTPTS, [movie] overlay=16:16 [out]

@end example

@section mptestsrc

Generate various test patterns, as generated by the MPlayer test filter.

The size of the generated video is fixed, and is 256x256.
This source is useful in particular for testing encoding features.

This source accepts an optional sequence of @var{key}=@var{value} pairs,
separated by ":". The description of the accepted options follows.

@table @option

@item rate, r
Specify the frame rate of the sourced video, as the number of frames
generated per second. It has to be a string in the format
@var{frame_rate_num}/@var{frame_rate_den}, an integer number, a float
number or a valid video frame rate abbreviation. The default value is
"25".

@item duration, d
Set the video duration of the sourced video. The accepted syntax is:
@example
[-]HH[:MM[:SS[.m...]]]
[-]S+[.m...]
@end example
See also the function @code{av_parse_time()}.

If not specified, or the expressed duration is negative, the video is
supposed to be generated forever.

@item test, t

Set the number or the name of the test to perform. Supported tests are:
@table @option
@item dc_luma
@item dc_chroma
@item freq_luma
@item freq_chroma
@item amp_luma
@item amp_chroma
@item cbp
@item mv
@item ring1
@item ring2
@item all
@end table

Default value is "all", which will cycle through the list of all tests.
@end table

For example the following:
@example
testsrc=t=dc_luma
@end example

will generate a "dc_luma" test pattern.

@section frei0r_src

Provide a frei0r source.

To enable compilation of this filter you need to install the frei0r
header and configure FFmpeg with --enable-frei0r.

The source supports the syntax:
@example
@var{size}:@var{rate}:@var{src_name}[@{=|:@}@var{param1}:@var{param2}:...:@var{paramN}]
@end example

@var{size} is the size of the video to generate, may be a string of the
form @var{width}x@var{height} or a frame size abbreviation.
@var{rate} is the rate of the video to generate, may be a string of
the form @var{num}/@var{den} or a frame rate abbreviation.
@var{src_name} is the name to the frei0r source to load. For more
information regarding frei0r and how to set the parameters read the
section @ref{frei0r} in the description of the video filters.

Some examples follow:
@example
# generate a frei0r partik0l source with size 200x200 and framerate 10
# which is overlayed on the overlay filter main input
frei0r_src=200x200:10:partik0l=1234 [overlay]; [in][overlay] overlay
@end example

@section nullsrc, rgbtestsrc, testsrc

The @code{nullsrc} source returns unprocessed video frames. It is
mainly useful to be employed in analysis / debugging tools, or as the
source for filters which ignore the input data.

The @code{rgbtestsrc} source generates an RGB test pattern useful for
detecting RGB vs BGR issues. You should see a red, green and blue
stripe from top to bottom.

The @code{testsrc} source generates a test video pattern, showing a
color pattern, a scrolling gradient and a timestamp. This is mainly
intended for testing purposes.

These sources accept an optional sequence of @var{key}=@var{value} pairs,
separated by ":". The description of the accepted options follows.

@table @option

@item size, s
Specify the size of the sourced video, it may be a string of the form
@var{width}x@var{heigth}, or the name of a size abbreviation. The
default value is "320x240".

@item rate, r
Specify the frame rate of the sourced video, as the number of frames
generated per second. It has to be a string in the format
@var{frame_rate_num}/@var{frame_rate_den}, an integer number, a float
number or a valid video frame rate abbreviation. The default value is
"25".

@item sar
Set the sample aspect ratio of the sourced video.

@item duration
Set the video duration of the sourced video. The accepted syntax is:
@example
[-]HH[:MM[:SS[.m...]]]
[-]S+[.m...]
@end example
See also the function @code{av_parse_time()}.

If not specified, or the expressed duration is negative, the video is
supposed to be generated forever.
@end table

For example the following:
@example
testsrc=duration=5.3:size=qcif:rate=10
@end example

will generate a video with a duration of 5.3 seconds, with size
176x144 and a framerate of 10 frames per second.

If the input content is to be ignored, @code{nullsrc} can be used. The
following command generates noise in the luminance plane by employing
the @code{mp=geq} filter:
@example
nullsrc=s=256x256, mp=geq=random(1)*255:128:128
@end example

@c man end VIDEO SOURCES

@chapter Video Sinks
@c man begin VIDEO SINKS

Below is a description of the currently available video sinks.

@section buffersink

Buffer video frames, and make them available to the end of the filter
graph.

This sink is mainly intended for a programmatic use, in particular
through the interface defined in @file{libavfilter/buffersink.h}.

It does not require a string parameter in input, but you need to
specify a pointer to a list of supported pixel formats terminated by
-1 in the opaque parameter provided to @code{avfilter_init_filter}
when initializing this sink.

@section nullsink

Null video sink, do absolutely nothing with the input video. It is
mainly useful as a template and to be employed in analysis / debugging
tools.

@c man end VIDEO SINKS