# Libavfilter Documentation

# Table of Contents

# 1. Introduction

Libavfilter is the filtering API of Libav. It is the substitute of the now deprecated ’vhooks’ and started as a Google Summer of Code project.

But note that there may still be serious bugs in the code and its API and ABI should not be considered stable yet!

# 2. Tutorial

In libavfilter, it is possible for filters to have multiple inputs and multiple outputs. To illustrate the sorts of things that are possible, we can use a complex filter graph. For example, the following one:

    input --> split --> fifo -----------------------> overlay --> output
                |                                        ^
                |                                        |
                +------> fifo --> crop --> vflip --------+

splits the stream in two streams, sends one stream through the crop filter and the vflip filter before merging it back with the other stream by overlaying it on top. You can use the following command to achieve this:

    ./avconv -i input -vf "[in] split [T1], fifo, [T2] overlay=0:H/2 [out]; [T1] fifo, crop=iw:ih/2:0:ih/2, vflip [T2]" output

The result will be that in output the top half of the video is mirrored onto the bottom half.

Video filters are loaded using the -vf option passed to avconv or to avplay. Filters in the same linear chain are separated by commas. In our example, split, fifo, overlay are in one linear chain, and fifo, crop, vflip are in another. The points where the linear chains join are labeled by names enclosed in square brackets. In our example, that is [T1] and [T2]. The magic labels [in] and [out] are the points where video is input and output.

Some filters take in input a list of parameters: they are specified after the filter name and an equal sign, and are separated each other by a semicolon.

There exist so-called source filters that do not have a video input, and we expect in the future some sink filters that will not have video output.

# 3. graph2dot

The ‘`graph2dot`’ program included in the Libav ‘`tools`’ directory can be used to parse a filter graph description and issue a corresponding textual representation in the dot language.

Invoke the command:

    graph2dot -h

to see how to use ‘`graph2dot`’.

You can then pass the dot description to the ‘`dot`’ program (from the graphviz suite of programs) and obtain a graphical representation of the filter graph.

For example the sequence of commands:

    echo GRAPH_DESCRIPTION | \
    tools/graph2dot -o graph.tmp && \
    dot -Tpng graph.tmp -o graph.png && \
    display graph.png

can be used to create and display an image representing the graph described by the GRAPH_DESCRIPTION string.

# 4. 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".

## 4.1 Filtergraph syntax

A filtergraph can be represented using a textual representation, which is recognized by the `-vf` and `-af` options in `avconv` and `avplay`, and by the `av_parse_graph()` function defined in ‘`libavfilter/avfiltergraph`’.

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: [in_link_1]...[in_link_N]filter_name=arguments[out_link_1]...[out_link_M]

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 "=arguments".

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 in_link_1 ... in_link_N, are associated to the filter input pads, the following labels out_link_1 ... 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:

    nullsrc, split[L1], [L2]overlay, nullsink

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:

    NAME             ::= sequence of alphanumeric characters and '_'
    LINKLABEL        ::= "[" NAME "]"
    LINKLABELS       ::= LINKLABEL [LINKLABELS]
    FILTER_ARGUMENTS ::= sequence of chars (eventually quoted)
    FILTER           ::= [LINKLABELS] NAME ["=" FILTER_ARGUMENTS] [LINKLABELS]
    FILTERCHAIN      ::= FILTER [,FILTERCHAIN]
    FILTERGRAPH      ::= FILTERCHAIN [;FILTERGRAPH]

# 5. Audio Filters

When you configure your Libav 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.

## 5.1 anull

Pass the audio source unchanged to the output.

# 6. Audio Sources

Below is a description of the currently available audio sources.

## 6.1 anullsrc

Null audio source, never return audio frames. It is mainly useful as a template and to be employed in analysis / debugging tools.

It accepts as optional parameter a string of the form sample_rate:channel_layout.

sample_rate specify the sample rate, and defaults to 44100.

channel_layout specify the channel layout, and can be either an integer or a string representing a channel layout. The default value of channel_layout is 3, which corresponds to CH_LAYOUT_STEREO.

Check the channel_layout_map definition in ‘`libavcodec/audioconvert.c`’ for the mapping between strings and channel layout values.

Follow some examples:

    #  set the sample rate to 48000 Hz and the channel layout to CH_LAYOUT_MONO.
    anullsrc=48000:4

    # same as
    anullsrc=48000:mono

# 7. Audio Sinks

Below is a description of the currently available audio sinks.

## 7.1 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.

# 8. Video Filters

When you configure your Libav 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.

## 8.1 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:

    blackframe[=amount:[threshold]]

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

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

## 8.2 boxblur

Apply boxblur algorithm to the input video.

This filter accepts the parameters: luma_power:luma_radius:chroma_radius:chroma_power:alpha_radius:alpha_power

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

luma_radius, chroma_radius, and 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:

‘`w, h`’

  the input width and height in pixels

‘`cw, ch`’

  the input chroma image width and height in pixels

‘`hsub, vsub`’

  horizontal and vertical chroma subsample values. For example for the pixel format "yuv422p" hsub is 2 and vsub is 1.

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

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

Some examples follow:

- Apply a boxblur filter with luma, chroma, and alpha radius set to 2:

      boxblur=2:1

- Set luma radius to 2, alpha and chroma radius to 0

      boxblur=2:1:0:0:0:0

- Set luma and chroma radius to a fraction of the video dimension

      boxblur=min(h\,w)/10:1:min(cw\,ch)/10:1

## 8.3 copy

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

## 8.4 crop

Crop the input video to out_w:out_h:x:y.

The parameters are expressions containing the following constants:

‘`E, PI, PHI`’

  the corresponding mathematical approximated values for e (euler number), pi (greek PI), PHI (golden ratio)

‘`x, y`’

  the computed values for x and y. They are evaluated for each new frame.

‘`in_w, in_h`’

  the input width and height

‘`iw, ih`’

  same as in_w and in_h

‘`out_w, out_h`’

  the output (cropped) width and height

‘`ow, oh`’

  same as out_w and out_h

‘`n`’

  the number of input frame, starting from 0

‘`pos`’

  the position in the file of the input frame, NAN if unknown

‘`t`’

  timestamp expressed in seconds, NAN if the input timestamp is unknown

The out_w and 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 out_w is "in_w", and the default value of out_h is "in_h".

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

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

The expression for x may depend on y, and the expression for y may depend on x.

Follow some examples:

    # 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)"

## 8.5 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:

    cropdetect[=limit[:round[:reset]]]

‘`limit`’

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

‘`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.

‘`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.

## 8.6 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 "x:y:w:h:band", or as a list of key=value pairs, separated by ":".

The description of the accepted parameters follows.

‘`x, y`’

  Specify the top left corner coordinates of the logo. They must be specified.

‘`w, h`’

  Specify the width and height of the logo to clear. They must be specified.

‘`band, t`’

  Specify the thickness of the fuzzy edge of the rectangle (added to w and h). The default value is 4.

‘`show`’

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

Some examples follow.

- Set a rectangle covering the area with top left corner coordinates 0,0 and size 100x77, setting a band of size 10:

      delogo=0:0:100:77:10

- As the previous example, but use named options:

      delogo=x=0:y=0:w=100:h=77:band=10

## 8.7 drawbox

Draw a colored box on the input image.

It accepts the syntax:

    drawbox=x:y:width:height:color

‘`x, y`’

  Specify the top left corner coordinates of the box. Default to 0.

‘`width, height`’

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

‘`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.

Follow some examples:

    # 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"

## 8.8 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 Libav with `--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 key=value pairs, separated by ":".

The description of the accepted parameters follows.

‘`fontfile`’

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

‘`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 textfile.

‘`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 text.

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

‘`x, y`’

  The offsets where text will be drawn within the video frame. Relative to the top/left border of the output image. They accept expressions similar to the overlay filter:

  ‘`x, y`’

    the computed values for x and y. They are evaluated for each new frame.

  ‘`main_w, main_h`’

    main input width and height

  ‘`W, H`’

    same as main_w and main_h

  ‘`text_w, text_h`’

    rendered text width and height

  ‘`w, h`’

    same as text_w and text_h

  ‘`n`’

    the number of frames processed, starting from 0

  ‘`t`’

    timestamp expressed in seconds, NAN if the input timestamp is unknown

  The default value of x and y is 0.

‘`fontsize`’

  The font size to be used for drawing text. The default value of fontsize is 16.

‘`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 fontcolor is "black".

‘`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 boxcolor is "white".

‘`box`’

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

‘`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".

‘`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 shadowcolor is "black".

‘`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:

  default
  no_scale
  no_hinting
  render
  no_bitmap
  vertical_layout
  force_autohint
  crop_bitmap
  pedantic
  ignore_global_advance_width
  no_recurse
  ignore_transform
  monochrome
  linear_design
  no_autohint
  end table

  Default value is "render".

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

‘`tabsize`’

  The size in number of spaces to use for rendering the tab. Default value is 4.

For example the command:

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

will draw "Test Text" with font FreeSerif, using the default values for the optional parameters.

The command:

    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"

will 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%.

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

For more information about libfreetype, check: http://www.freetype.org/.

## 8.9 fade

Apply fade-in/out effect to input video.

It accepts the parameters: type:start_frame:nb_frames

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

start_frame specifies the number of the start frame for starting to apply the fade effect.

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.

    # 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

## 8.10 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:

‘`0 or bff`’

  output bottom field first

‘`1 or tff`’

  output top field first

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:

    ./avconv -i in.vob -vf "fieldorder=bff" out.dv

## 8.11 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.

## 8.12 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:

    # 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

## 8.13 frei0r

Apply a frei0r effect to the input video.

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

The filter supports the syntax:

    filter_name[{:|=}param1:param2:...:paramN]

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

param1, param2, ... , 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 R/G/B, R, G, and B being float numbers from 0.0 to 1.0) or by an `av_parse_color()` color description), a position (specified by the syntax X/Y, X and 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:

    # 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

For more information see: http://piksel.org/frei0r

## 8.14 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 ’:’: strength:radius

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.

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.

    # default parameters
    gradfun=1.2:16

    # omitting radius
    gradfun=1.2

## 8.15 hflip

Flip the input video horizontally.

For example to horizontally flip the input video with `avconv`:

    avconv -i in.avi -vf "hflip" out.avi

## 8.16 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: luma_spatial:chroma_spatial:luma_tmp:chroma_tmp

‘`luma_spatial`’

  a non-negative float number which specifies spatial luma strength, defaults to 4.0

‘`chroma_spatial`’

  a non-negative float number which specifies spatial chroma strength, defaults to 3.0*luma_spatial/4.0

‘`luma_tmp`’

  a float number which specifies luma temporal strength, defaults to 6.0*luma_spatial/4.0

‘`chroma_tmp`’

  a float number which specifies chroma temporal strength, defaults to luma_tmp*chroma_spatial/luma_spatial

## 8.17 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.

lutyuv applies a lookup table to a YUV input video, 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 lut filter requires either YUV or RGB pixel formats in input, and accepts the options:

  c0 (first pixel component) c1 (second pixel component) c2 (third pixel component) c3 (fourth pixel component, corresponds to the alpha component)

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

The lutrgb filter requires RGB pixel formats in input, and accepts the options:

  r (red component) g (green component) b (blue component) a (alpha component)

The lutyuv filter requires YUV pixel formats in input, and accepts the options:

  y (Y/luminance component) u (U/Cb component) v (V/Cr component) a (alpha component)

The expressions can contain the following constants and functions:

‘`E, PI, PHI`’

  the corresponding mathematical approximated values for e (euler number), pi (greek PI), PHI (golden ratio)

‘`w, h`’

  the input width and height

‘`val`’

  input value for the pixel component

‘`clipval`’

  the input value clipped in the minval-maxval range

‘`maxval`’

  maximum value for the pixel component

‘`minval`’

  minimum value for the pixel component

‘`negval`’

  the negated value for the pixel component value clipped in the minval-maxval range , it corresponds to the expression "maxval-clipval+minval"

‘`clip(val)`’

  the computed value in val clipped in the minval-maxval range

‘`gammaval(gamma)`’

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

All expressions default to "val".

Some examples follow:

    # 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=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)

## 8.18 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.

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:

    # 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

## 8.19 null

Pass the video source unchanged to the output.

## 8.20 ocv

Apply video transform using libopencv.

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

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

filter_name is the name of the libopencv filter to apply.

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 information: http://opencv.willowgarage.com/documentation/c/image_filtering.html

Follows the list of supported libopencv filters.

### 8.20.1 dilate

Dilate an image by using a specific structuring element. This filter corresponds to the libopencv function `cvDilate`.

It accepts the parameters: struct_el:nb_iterations.

struct_el represents a structuring element, and has the syntax: colsxrows+anchor_xxanchor_y/shape

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

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

The default value for struct_el is "3x3+0x0/rect".

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

Follow some 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

### 8.20.2 erode

Erode an image by using a specific structuring element. This filter corresponds to the libopencv function `cvErode`.

The filter accepts the parameters: struct_el:nb_iterations, with the same syntax and semantics as the dilate filter.

### 8.20.3 smooth

Smooth the input video.

The filter takes the following parameters: type:param1:param2:param3:param4.

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".

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

The default value for param1 is 3, the default value for the other parameters is 0.

These parameters correspond to the parameters assigned to the libopencv function `cvSmooth`.

## 8.21 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: x:y.

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

‘`main_w, main_h`’

  main input width and height

‘`W, H`’

  same as main_w and main_h

‘`overlay_w, overlay_h`’

  overlay input width and height

‘`w, h`’

  same as overlay_w and overlay_h

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 setpts=PTS-STARTPTS filter to have them begin in the same zero timestamp, as it does the example for the movie filter.

Follow some examples:

    # 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]

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

## 8.22 pad

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

It accepts the following parameters: width:height:x:y:color.

The parameters width, height, x, and y are expressions containing the following constants:

‘`E, PI, PHI`’

  the corresponding mathematical approximated values for e (euler number), pi (greek PI), phi (golden ratio)

‘`in_w, in_h`’

  the input video width and height

‘`iw, ih`’

  same as in_w and in_h

‘`out_w, out_h`’

  the output width and height, that is the size of the padded area as specified by the width and height expressions

‘`ow, oh`’

  same as out_w and out_h

‘`x, y`’

  x and y offsets as specified by the x and y expressions, or NAN if not yet specified

‘`a`’

  input display aspect ratio, same as iw / ih

‘`hsub, vsub`’

  horizontal and vertical chroma subsample values. For example for the pixel format "yuv422p" hsub is 2 and vsub is 1.

Follows the description of the accepted parameters.

‘`width, height`’

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

  The width expression can reference the value set by the height expression, and vice versa.

  The default value of width and height is 0.

‘`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 x expression can reference the value set by the y expression, and vice versa.

  The default value of x and y is 0.

‘`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 color is "black".

Some examples follow:

    # 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"

    # 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"

## 8.23 pixdesctest

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

For example:

    format=monow, pixdesctest

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

## 8.24 scale

Scale the input video to width:height and/or convert the image format.

The parameters width and height are expressions containing the following constants:

‘`E, PI, PHI`’

  the corresponding mathematical approximated values for e (euler number), pi (greek PI), phi (golden ratio)

‘`in_w, in_h`’

  the input width and height

‘`iw, ih`’

  same as in_w and in_h

‘`out_w, out_h`’

  the output (cropped) width and height

‘`ow, oh`’

  same as out_w and out_h

‘`dar, a`’

  input display aspect ratio, same as iw / ih

‘`sar`’

  input sample aspect ratio

‘`hsub, vsub`’

  horizontal and vertical chroma subsample values. For example for the pixel format "yuv422p" hsub is 2 and vsub is 1.

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 width or height is 0, the respective input size is used for the output.

If the value for width or 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 width and height is 0.

Some examples follow:

    # 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'

## 8.25 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:

‘`PI`’

  Greek PI

‘`PHI`’

  golden ratio

‘`E`’

  Euler number

‘`n`’

  the sequential number of the filtered frame, starting from 0

‘`selected_n`’

  the sequential number of the selected frame, starting from 0

‘`prev_selected_n`’

  the sequential number of the last selected frame, NAN if undefined

‘`TB`’

  timebase of the input timestamps

‘`pts`’

  the PTS (Presentation TimeStamp) of the filtered video frame, expressed in TB units, NAN if undefined

‘`t`’

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

‘`prev_pts`’

  the PTS of the previously filtered video frame, NAN if undefined

‘`prev_selected_pts`’

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

‘`prev_selected_t`’

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

‘`start_pts`’

  the PTS of the first video frame in the video, NAN if undefined

‘`start_t`’

  the time of the first video frame in the video, NAN if undefined

‘`pict_type`’

  the type of the filtered frame, can assume one of the following values:

  ‘`I`’
  ‘`P`’
  ‘`B`’
  ‘`S`’
  ‘`SI`’
  ‘`SP`’
  ‘`BI`’
‘`interlace_type`’

  the frame interlace type, can assume one of the following values:

  ‘`PROGRESSIVE`’

    the frame is progressive (not interlaced)

  ‘`TOPFIRST`’

    the frame is top-field-first

  ‘`BOTTOMFIRST`’

    the frame is bottom-field-first

‘`key`’

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

‘`pos`’

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

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

Some examples follow:

    # 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)'

## 8.26 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: 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 num:den, where num and 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:

    setdar=16:9
    # the above is equivalent to
    setdar=1.77777

See also the setsar filter documentation.

## 8.27 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:

‘`PTS`’

  the presentation timestamp in input

‘`PI`’

  Greek PI

‘`PHI`’

  golden ratio

‘`E`’

  Euler number

‘`N`’

  the count of the input frame, starting from 0.

‘`STARTPTS`’

  the PTS of the first video frame

‘`INTERLACED`’

  tell if the current frame is interlaced

‘`POS`’

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

‘`PREV_INPTS`’

  previous input PTS

‘`PREV_OUTPTS`’

  previous output PTS

Some examples follow:

    # 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))'

## 8.28 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: 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 num:den, where num and 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:

    setsar=10:11

## 8.29 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 "PI", "E", "PHI", "AVTB" (the default timebase), and "intb" (the input timebase).

The default value for the input is "intb".

Follow some examples.

    # 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

## 8.30 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 key:value.

A description of each shown parameter follows:

‘`n`’

  sequential number of the input frame, starting from 0

‘`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.

‘`pts_time`’

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

‘`pos`’

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

‘`fmt`’

  pixel format name

‘`sar`’

  sample aspect ratio of the input frame, expressed in the form num/den

‘`s`’

  size of the input frame, expressed in the form widthxheight

‘`i`’

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

‘`iskey`’

  1 if the frame is a key frame, 0 otherwise

‘`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 `AVPictureType` enum and of the `av_get_picture_type_char` function defined in ‘`libavutil/avutil.h`’.

‘`checksum`’

  Adler-32 checksum of all the planes of the input frame

‘`plane_checksum`’

  Adler-32 checksum of each plane of the input frame, expressed in the form "[c0 c1 c2 c3]"

## 8.31 slicify

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

    ./avconv -i in.avi -vf "slicify=32" out.avi

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.

## 8.32 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:

‘`0`’

  Rotate by 90 degrees counterclockwise and vertically flip (default), that is:

      L.R     L.l
      . . ->  . .
      l.r     R.r

‘`1`’

  Rotate by 90 degrees clockwise, that is:

      L.R     l.L
      . . ->  . .
      l.r     r.R

‘`2`’

  Rotate by 90 degrees counterclockwise, that is:

      L.R     R.r
      . . ->  . .
      l.r     L.l

‘`3`’

  Rotate by 90 degrees clockwise and vertically flip, that is:

      L.R     r.R
      . . ->  . .
      l.r     l.L

## 8.33 unsharp

Sharpen or blur the input video.

It accepts the following parameters: luma_msize_x:luma_msize_y:luma_amount:chroma_msize_x:chroma_msize_y: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’.

‘`luma_msize_x`’

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

‘`luma_msize_y`’

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

‘`luma_amount`’

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

‘`chroma_msize_x`’

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

‘`chroma_msize_y`’

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

‘`luma_amount`’

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

    # 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 avconv
    ./avconv -i in.avi -vf "unsharp" out.mp4

## 8.34 vflip

Flip the input video vertically.

    ./avconv -i in.avi -vf "vflip" out.avi

## 8.35 yadif

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

It accepts the optional parameters: mode:parity:auto.

mode specifies the interlacing mode to adopt, accepts one of the following values:

‘`0`’

  output 1 frame for each frame

‘`1`’

  output 1 frame for each field

‘`2`’

  like 0 but skips spatial interlacing check

‘`3`’

  like 1 but skips spatial interlacing check

Default value is 0.

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

‘`0`’

  assume top field first

‘`1`’

  assume bottom field first

‘`-1`’

  enable automatic detection

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

auto specifies if deinterlacer should trust the interlaced flag and only deinterlace frames marked as interlaced

‘`0`’

  deinterlace all frames

‘`1`’

  only deinterlace frames marked as interlaced

Default value is 0.

# 9. Video Sources

Below is a description of the currently available video sources.

## 9.1 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 ‘`libavfilter/vsrc_buffer.h`’.

It accepts the following parameters: width:height:pix_fmt_string:timebase_num:timebase_den:sample_aspect_ratio_num:sample_aspect_ratio.den

All the parameters need to be explicitly defined.

Follows the list of the accepted parameters.

‘`width, height`’

  Specify the width and height of the buffered video frames.

‘`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.

‘`timebase_num, timebase_den`’

  Specify numerator and denomitor of the timebase assumed by the timestamps of the buffered frames.

‘`sample_aspect_ratio.num, sample_aspect_ratio.den`’

  Specify numerator and denominator of the sample aspect ratio assumed by the video frames.

For example:

    buffer=320:240:yuv410p:1:24:1:1

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 ‘`libavutil/pixfmt.h`’), this example corresponds to:

    buffer=320:240:6:1:24

## 9.2 color

Provide an uniformly colored input.

It accepts the following parameters: color:frame_size:frame_rate

Follows the description of the accepted parameters.

‘`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".

‘`frame_size`’

  Specify the size of the sourced video, it may be a string of the form widthxheight, or the name of a size abbreviation. The default value is "320x240".

‘`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 frame_rate_num/frame_rate_den, an integer number, a float number or a valid video frame rate abbreviation. The default value is "25".

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".

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

## 9.3 movie

Read a video stream from a movie container.

It accepts the syntax: movie_name[:options] where 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 options is an optional sequence of key=value pairs, separated by ":".

The description of the accepted options follows.

‘`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 movie_name or by probing.

‘`seek_point, sp`’

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

‘`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".

This filter allows to overlay a second video on top of main input of a filtergraph as shown in this graph:

    input -----------> deltapts0 --> overlay --> output
                                        ^
                                        |
    movie --> scale--> deltapts1 -------+

Some examples follow:

    # 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]

## 9.4 nullsrc

Null video source, never return images. It is mainly useful as a template and to be employed in analysis / debugging tools.

It accepts as optional parameter a string of the form width:height:timebase.

width and height specify the size of the configured source. The default values of width and height are respectively 352 and 288 (corresponding to the CIF size format).

timebase specifies an arithmetic expression representing a timebase. The expression can contain the constants "PI", "E", "PHI", "AVTB" (the default timebase), and defaults to the value "AVTB".

## 9.5 frei0r_src

Provide a frei0r source.

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

The source supports the syntax:

    size:rate:src_name[{=|:}param1:param2:...:paramN]

size is the size of the video to generate, may be a string of the form widthxheight or a frame size abbreviation. rate is the rate of the video to generate, may be a string of the form num/den or a frame rate abbreviation. 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 frei0r in the description of the video filters.

Some examples follow:

    # 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

## 9.6 rgbtestsrc, testsrc

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

Both sources accept an optional sequence of key=value pairs, separated by ":". The description of the accepted options follows.

‘`size, s`’

  Specify the size of the sourced video, it may be a string of the form widthxheight, or the name of a size abbreviation. The default value is "320x240".

‘`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 frame_rate_num/frame_rate_den, an integer number, a float number or a valid video frame rate abbreviation. The default value is "25".

‘`sar`’

  Set the sample aspect ratio of the sourced video.

‘`duration`’

  Set the video duration of the sourced video. The accepted syntax is:

      [-]HH[:MM[:SS[.m...]]]
      [-]S+[.m...]

  See also the function `av_parse_time()`.

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

For example the following:

    testsrc=duration=5.3:size=qcif:rate=10

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

# 10. Video Sinks

Below is a description of the currently available video sinks.

## 10.1 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.