path: root/doc/filters.texi

@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 anull

Pass the audio source unchanged to the output.

@c man end AUDIO FILTERS

@chapter Audio Sources
@c man begin AUDIO SOURCES

Below is a description of the currently available audio sources.

@section 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
@var{sample_rate}:@var{channel_layout}.

@var{sample_rate} specify the sample rate, and defaults to 44100.

@var{channel_layout} 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 3, which corresponds to CH_LAYOUT_STEREO.

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

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

# same as
anullsrc=48000: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 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 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 E, PI, PHI
the corresponding mathematical approximated values for e
(euler number), pi (greek PI), PHI (golden ratio)

@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 heigth

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

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

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

@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 lefth 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 and position
"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 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 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".

The following command:

@example
./ffmpeg -i in.avi -vf "format=yuv420p" out.avi
@end example

will convert the input video to the format "yuv420p".

@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 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 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".

The following command:

@example
./ffmpeg -i in.avi -vf "noformat=yuv420p, vflip" out.avi
@end example

will make libavfilter use a format different from "yuv420p" for the
input to the vflip filter.

@section null

Pass the video source unchanged to the output.

@section ocv_smooth

Apply smooth transform using libopencv.

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

The filter accepts 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}. Refer to the official libopencv
documentation for the exact meaning of the parameters:
@url{http://opencv.willowgarage.com/documentation/c/image_filtering.html}

@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=0:png: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=0:png:logo1.png [logo1];
movie=0:png: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}.

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 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 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

For example:

@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
# row 0, column 40.
pad=640:480:0:40:violet
@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} and/or convert the image format.

For example the command:

@example
./ffmpeg -i in.avi -vf "scale=200:100" out.avi
@end example

will scale the input video to a size of 200x100.

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.

@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 PI
Greek PI

@item PHI
golden ratio

@item E
Euler number

@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

@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 "PI", "E", "PHI", "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 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 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 '5:5:1.0:0:0:0.0'.

@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 0.

@item chroma_msize_y
Set the chroma matrix vertical size. It can be an integer between 3
and 13, default value is 0.

@item luma_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

yadif is "yet another deinterlacing filter".

It accepts the syntax:
@example
yadif=[@var{mode}[:@var{parity}]]
@end example

@table @option

@item mode
Specify 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.

@item parity
0 if is bottom field first, 1 if the interlaced video is top field
first, -1 to enable automatic detection.

@end table

@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}

All the parameters 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.
@end table

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

will instruct the source to accept video frames with size 320x240 and
with format "yuv410p" and assuming 1/24 as the timestamps timebase.
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
@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{heigth}, 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 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
@var{width}:@var{height}:@var{timebase}.

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

@var{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".

@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 "frei0r" (@pxref{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

@c man end VIDEO SOURCES

@chapter Video Sinks
@c man begin VIDEO SINKS

Below is a description of the currently available video sinks.

@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