1 @chapter Filtergraph description
2 @c man begin FILTERGRAPH DESCRIPTION
4 A filtergraph is a directed graph of connected filters. It can contain
5 cycles, and there can be multiple links between a pair of
6 filters. Each link has one input pad on one side connecting it to one
7 filter from which it takes its input, and one output pad on the other
8 side connecting it to the one filter accepting its output.
10 Each filter in a filtergraph is an instance of a filter class
11 registered in the application, which defines the features and the
12 number of input and output pads of the filter.
14 A filter with no input pads is called a "source", a filter with no
15 output pads is called a "sink".
17 @section Filtergraph syntax
19 A filtergraph can be represented using a textual representation, which
20 is recognized by the @code{-vf} and @code{-af} options of the ff*
21 tools, and by the @code{av_parse_graph()} function defined in
22 @file{libavfilter/avfiltergraph}.
24 A filterchain consists of a sequence of connected filters, each one
25 connected to the previous one in the sequence. A filterchain is
26 represented by a list of ","-separated filter descriptions.
28 A filtergraph consists of a sequence of filterchains. A sequence of
29 filterchains is represented by a list of ";"-separated filterchain
32 A filter is represented by a string of the form:
33 [@var{in_link_1}]...[@var{in_link_N}]@var{filter_name}=@var{arguments}[@var{out_link_1}]...[@var{out_link_M}]
35 @var{filter_name} is the name of the filter class of which the
36 described filter is an instance of, and has to be the name of one of
37 the filter classes registered in the program.
38 The name of the filter class is optionally followed by a string
41 @var{arguments} is a string which contains the parameters used to
42 initialize the filter instance, and are described in the filter
45 The list of arguments can be quoted using the character "'" as initial
46 and ending mark, and the character '\' for escaping the characters
47 within the quoted text; otherwise the argument string is considered
48 terminated when the next special character (belonging to the set
49 "[]=;,") is encountered.
51 The name and arguments of the filter are optionally preceded and
52 followed by a list of link labels.
53 A link label allows to name a link and associate it to a filter output
54 or input pad. The preceding labels @var{in_link_1}
55 ... @var{in_link_N}, are associated to the filter input pads,
56 the following labels @var{out_link_1} ... @var{out_link_M}, are
57 associated to the output pads.
59 When two link labels with the same name are found in the
60 filtergraph, a link between the corresponding input and output pad is
63 If an output pad is not labelled, it is linked by default to the first
64 unlabelled input pad of the next filter in the filterchain.
65 For example in the filterchain:
67 nullsrc, split[L1], [L2]overlay, nullsink
69 the split filter instance has two output pads, and the overlay filter
70 instance two input pads. The first output pad of split is labelled
71 "L1", the first input pad of overlay is labelled "L2", and the second
72 output pad of split is linked to the second input pad of overlay,
73 which are both unlabelled.
75 In a complete filterchain all the unlabelled filter input and output
76 pads must be connected. A filtergraph is considered valid if all the
77 filter input and output pads of all the filterchains are connected.
79 Follows a BNF description for the filtergraph syntax:
81 @var{NAME} ::= sequence of alphanumeric characters and '_'
82 @var{LINKLABEL} ::= "[" @var{NAME} "]"
83 @var{LINKLABELS} ::= @var{LINKLABEL} [@var{LINKLABELS}]
84 @var{FILTER_ARGUMENTS} ::= sequence of chars (eventually quoted)
85 @var{FILTER} ::= [@var{LINKNAMES}] @var{NAME} ["=" @var{ARGUMENTS}] [@var{LINKNAMES}]
86 @var{FILTERCHAIN} ::= @var{FILTER} [,@var{FILTERCHAIN}]
87 @var{FILTERGRAPH} ::= @var{FILTERCHAIN} [;@var{FILTERGRAPH}]
90 @c man end FILTERGRAPH DESCRIPTION
92 @chapter Audio Filters
93 @c man begin AUDIO FILTERS
95 When you configure your FFmpeg build, you can disable any of the
96 existing filters using --disable-filters.
97 The configure output will show the audio filters included in your
100 Below is a description of the currently available audio filters.
104 Pass the audio source unchanged to the output.
106 @c man end AUDIO FILTERS
108 @chapter Audio Sources
109 @c man begin AUDIO SOURCES
111 Below is a description of the currently available audio sources.
115 Null audio source, never return audio frames. It is mainly useful as a
116 template and to be employed in analysis / debugging tools.
118 It accepts as optional parameter a string of the form
119 @var{sample_rate}:@var{channel_layout}.
121 @var{sample_rate} specify the sample rate, and defaults to 44100.
123 @var{channel_layout} specify the channel layout, and can be either an
124 integer or a string representing a channel layout. The default value
125 of @var{channel_layout} is 3, which corresponds to CH_LAYOUT_STEREO.
127 Check the channel_layout_map definition in
128 @file{libavcodec/audioconvert.c} for the mapping between strings and
129 channel layout values.
131 Follow some examples:
133 # set the sample rate to 48000 Hz and the channel layout to CH_LAYOUT_MONO.
140 @c man end AUDIO SOURCES
143 @c man begin AUDIO SINKS
145 Below is a description of the currently available audio sinks.
149 Null audio sink, do absolutely nothing with the input audio. It is
150 mainly useful as a template and to be employed in analysis / debugging
153 @c man end AUDIO SINKS
155 @chapter Video Filters
156 @c man begin VIDEO FILTERS
158 When you configure your FFmpeg build, you can disable any of the
159 existing filters using --disable-filters.
160 The configure output will show the video filters included in your
163 Below is a description of the currently available video filters.
167 Detect frames that are (almost) completely black. Can be useful to
168 detect chapter transitions or commercials. Output lines consist of
169 the frame number of the detected frame, the percentage of blackness,
170 the position in the file if known or -1 and the timestamp in seconds.
172 In order to display the output lines, you need to set the loglevel at
173 least to the AV_LOG_INFO value.
175 The filter accepts the syntax:
177 blackframe[=@var{amount}:[@var{threshold}]]
180 @var{amount} is the percentage of the pixels that have to be below the
181 threshold, and defaults to 98.
183 @var{threshold} is the threshold below which a pixel value is
184 considered black, and defaults to 32.
188 Copy the input source unchanged to the output. Mainly useful for
193 Crop the input video to @var{out_w}:@var{out_h}:@var{x}:@var{y}.
195 The parameters are expressions containing the following constants:
199 the corresponding mathematical approximated values for e
200 (euler number), pi (greek PI), PHI (golden ratio)
203 the computed values for @var{x} and @var{y}. They are evaluated for
207 the input width and heigth
210 same as @var{in_w} and @var{in_h}
213 the output (cropped) width and heigth
216 same as @var{out_w} and @var{out_h}
219 the number of input frame, starting from 0
222 the position in the file of the input frame, NAN if unknown
225 timestamp expressed in seconds, NAN if the input timestamp is unknown
229 The @var{out_w} and @var{out_h} parameters specify the expressions for
230 the width and height of the output (cropped) video. They are
231 evaluated just at the configuration of the filter.
233 The default value of @var{out_w} is "in_w", and the default value of
234 @var{out_h} is "in_h".
236 The expression for @var{out_w} may depend on the value of @var{out_h},
237 and the expression for @var{out_h} may depend on @var{out_w}, but they
238 cannot depend on @var{x} and @var{y}, as @var{x} and @var{y} are
239 evaluated after @var{out_w} and @var{out_h}.
241 The @var{x} and @var{y} parameters specify the expressions for the
242 position of the top-left corner of the output (non-cropped) area. They
243 are evaluated for each frame. If the evaluated value is not valid, it
244 is approximated to the nearest valid value.
246 The default value of @var{x} is "(in_w-out_w)/2", and the default
247 value for @var{y} is "(in_h-out_h)/2", which set the cropped area at
248 the center of the input image.
250 The expression for @var{x} may depend on @var{y}, and the expression
251 for @var{y} may depend on @var{x}.
253 Follow some examples:
255 # crop the central input area with size 100x100
258 # crop the central input area with size 2/3 of the input video
259 "crop=2/3*in_w:2/3*in_h"
261 # crop the input video central square
264 # delimit the rectangle with the top-left corner placed at position
265 # 100:100 and the right-bottom corner corresponding to the right-bottom
266 # corner of the input image.
267 crop=in_w-100:in_h-100:100:100
269 # crop 10 pixels from the left and right borders, and 20 pixels from
270 # the top and bottom borders
271 "crop=in_w-2*10:in_h-2*20"
273 # keep only the bottom right quarter of the input image
274 "crop=in_w/2:in_h/2:in_w/2:in_h/2"
276 # crop height for getting Greek harmony
277 "crop=in_w:1/PHI*in_w"
280 "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)"
282 # erratic camera effect depending on timestamp
283 "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)"
285 # set x depending on the value of y
286 "crop=in_w/2:in_h/2:y:10+10*sin(n/10)"
291 Auto-detect crop size.
293 Calculate necessary cropping parameters and prints the recommended
294 parameters through the logging system. The detected dimensions
295 correspond to the non-black area of the input video.
297 It accepts the syntax:
299 cropdetect[=@var{limit}[:@var{round}[:@var{reset}]]]
305 Threshold, which can be optionally specified from nothing (0) to
306 everything (255), defaults to 24.
309 Value which the width/height should be divisible by, defaults to
310 16. The offset is automatically adjusted to center the video. Use 2 to
311 get only even dimensions (needed for 4:2:2 video). 16 is best when
312 encoding to most video codecs.
315 Counter that determines after how many frames cropdetect will reset
316 the previously detected largest video area and start over to detect
317 the current optimal crop area. Defaults to 0.
319 This can be useful when channel logos distort the video area. 0
320 indicates never reset and return the largest area encountered during
326 Draw a colored box on the input image.
328 It accepts the syntax:
330 drawbox=@var{x}:@var{y}:@var{width}:@var{height}:@var{color}
336 Specify the top left corner coordinates of the box. Default to 0.
339 Specify the width and height of the box, if 0 they are interpreted as
340 the input width and height. Default to 0.
343 Specify the color of the box to write, it can be the name of a color
344 (case insensitive match) or a 0xRRGGBB[AA] sequence.
347 Follow some examples:
349 # draw a black box around the edge of the input image
352 # draw a box with color red and an opacity of 50%
353 drawbox=10:20:200:60:red@@0.5"
358 Draw text string or text from specified file on top of video using the
361 To enable compilation of this filter you need to configure FFmpeg with
362 @code{--enable-libfreetype}.
364 The filter also recognizes strftime() sequences in the provided text
365 and expands them accordingly. Check the documentation of strftime().
367 The filter accepts parameters as a list of @var{key}=@var{value} pairs,
370 The description of the accepted parameters follows.
375 The font file to be used for drawing text. Path must be included.
376 This parameter is mandatory.
379 The text string to be drawn. The text must be a sequence of UTF-8
381 This parameter is mandatory if no file is specified with the parameter
385 A text file containing text to be drawn. The text must be a sequence
386 of UTF-8 encoded characters.
388 This parameter is mandatory if no text string is specified with the
389 parameter @var{text}.
391 If both text and textfile are specified, an error is thrown.
394 The offsets where text will be drawn within the video frame.
395 Relative to the top/left border of the output image.
397 The default value of @var{x} and @var{y} is 0.
400 The font size to be used for drawing text.
401 The default value of @var{fontsize} is 16.
404 The color to be used for drawing fonts.
405 Either a string (e.g. "red") or in 0xRRGGBB[AA] format
406 (e.g. "0xff000033"), possibly followed by an alpha specifier.
407 The default value of @var{fontcolor} is "black".
410 The color to be used for drawing box around text.
411 Either a string (e.g. "yellow") or in 0xRRGGBB[AA] format
412 (e.g. "0xff00ff"), possibly followed by an alpha specifier.
413 The default value of @var{boxcolor} is "white".
416 Used to draw a box around text using background color.
417 Value should be either 1 (enable) or 0 (disable).
418 The default value of @var{box} is 0.
420 @item shadowx, shadowy
421 The x and y offsets for the text shadow position with respect to the
422 position of the text. They can be either positive or negative
423 values. Default value for both is "0".
426 The color to be used for drawing a shadow behind the drawn text. It
427 can be a color name (e.g. "yellow") or a string in the 0xRRGGBB[AA]
428 form (e.g. "0xff00ff"), possibly followed by an alpha specifier.
429 The default value of @var{shadowcolor} is "black".
432 Flags to be used for loading the fonts.
434 The flags map the corresponding flags supported by libfreetype, and are
435 a combination of the following values:
442 @item vertical_layout
446 @item ignore_global_advance_width
448 @item ignore_transform
455 Default value is "render".
457 For more information consult the documentation for the FT_LOAD_*
461 The size in number of spaces to use for rendering the tab.
465 For example the command:
467 drawtext="fontfile=/usr/share/fonts/truetype/freefont/FreeSerif.ttf: text='Test Text'"
470 will draw "Test Text" with font FreeSerif, using the default values
471 for the optional parameters.
475 drawtext="fontfile=/usr/share/fonts/truetype/freefont/FreeSerif.ttf: text='Test Text':\
476 x=100: y=50: fontsize=24: fontcolor=yellow@@0.2: box=1: boxcolor=red@@0.2"
479 will draw 'Test Text' with font FreeSerif of size 24 at position x=100
480 and y=50 (counting from the top-left corner of the screen), text is
481 yellow with a red box around it. Both the text and the box have an
484 Note that the double quotes are not necessary if spaces are not used
485 within the parameter list.
487 For more information about libfreetype, check:
488 @url{http://www.freetype.org/}.
492 Apply fade-in/out effect to input video.
494 It accepts the parameters:
495 @var{type}:@var{start_frame}:@var{nb_frames}
497 @var{type} specifies if the effect type, can be either "in" for
498 fade-in, or "out" for a fade-out effect.
500 @var{start_frame} specifies the number of the start frame for starting
501 to apply the fade effect.
503 @var{nb_frames} specifies the number of frames for which the fade
504 effect has to last. At the end of the fade-in effect the output video
505 will have the same intensity as the input video, at the end of the
506 fade-out transition the output video will be completely black.
508 A few usage examples follow, usable too as test scenarios.
510 # fade in first 30 frames of video
513 # fade out last 45 frames of a 200-frame video
516 # fade in first 25 frames and fade out last 25 frames of a 1000-frame video
517 fade=in:0:25, fade=out:975:25
519 # make first 5 frames black, then fade in from frame 5-24
525 Transform the field order of the input video.
527 It accepts one parameter which specifies the required field order that
528 the input interlaced video will be transformed to. The parameter can
529 assume one of the following values:
533 output bottom field first
535 output top field first
538 Default value is "tff".
540 Transformation is achieved by shifting the picture content up or down
541 by one line, and filling the remaining line with appropriate picture content.
542 This method is consistent with most broadcast field order converters.
544 If the input video is not flagged as being interlaced, or it is already
545 flagged as being of the required output field order then this filter does
546 not alter the incoming video.
548 This filter is very useful when converting to or from PAL DV material,
549 which is bottom field first.
553 ./ffmpeg -i in.vob -vf "fieldorder=bff" out.dv
558 Buffer input images and send them when they are requested.
560 This filter is mainly useful when auto-inserted by the libavfilter
563 The filter does not take parameters.
567 Convert the input video to one of the specified pixel formats.
568 Libavfilter will try to pick one that is supported for the input to
571 The filter accepts a list of pixel format names, separated by ":",
572 for example "yuv420p:monow:rgb24".
574 Some examples follow:
576 # convert the input video to the format "yuv420p"
579 # convert the input video to any of the formats in the list
580 format=yuv420p:yuv444p:yuv410p
586 Apply a frei0r effect to the input video.
588 To enable compilation of this filter you need to install the frei0r
589 header and configure FFmpeg with --enable-frei0r.
591 The filter supports the syntax:
593 @var{filter_name}[@{:|=@}@var{param1}:@var{param2}:...:@var{paramN}]
596 @var{filter_name} is the name to the frei0r effect to load. If the
597 environment variable @env{FREI0R_PATH} is defined, the frei0r effect
598 is searched in each one of the directories specified by the colon
599 separated list in @env{FREIOR_PATH}, otherwise in the standard frei0r
600 paths, which are in this order: @file{HOME/.frei0r-1/lib/},
601 @file{/usr/local/lib/frei0r-1/}, @file{/usr/lib/frei0r-1/}.
603 @var{param1}, @var{param2}, ... , @var{paramN} specify the parameters
604 for the frei0r effect.
606 A frei0r effect parameter can be a boolean (whose values are specified
607 with "y" and "n"), a double, a color (specified by the syntax
608 @var{R}/@var{G}/@var{B}, @var{R}, @var{G}, and @var{B} being float
609 numbers from 0.0 to 1.0) or by an @code{av_parse_color()} color
610 description), a position (specified by the syntax @var{X}/@var{Y},
611 @var{X} and @var{Y} being float numbers) and a string.
613 The number and kind of parameters depend on the loaded effect. If an
614 effect parameter is not specified the default value is set.
616 Some examples follow:
618 # apply the distort0r effect, set the first two double parameters
619 frei0r=distort0r:0.5:0.01
621 # apply the colordistance effect, takes a color as first parameter
622 frei0r=colordistance:0.2/0.3/0.4
623 frei0r=colordistance:violet
624 frei0r=colordistance:0x112233
626 # apply the perspective effect, specify the top left and top right
628 frei0r=perspective:0.2/0.2:0.8/0.2
631 For more information see:
632 @url{http://piksel.org/frei0r}
636 Fix the banding artifacts that are sometimes introduced into nearly flat
637 regions by truncation to 8bit colordepth.
638 Interpolate the gradients that should go where the bands are, and
641 This filter is designed for playback only. Do not use it prior to
642 lossy compression, because compression tends to lose the dither and
643 bring back the bands.
645 The filter takes two optional parameters, separated by ':':
646 @var{strength}:@var{radius}
648 @var{strength} is the maximum amount by which the filter will change
649 any one pixel. Also the threshold for detecting nearly flat
650 regions. Acceptable values range from .51 to 255, default value is
651 1.2, out-of-range values will be clipped to the valid range.
653 @var{radius} is the neighborhood to fit the gradient to. A larger
654 radius makes for smoother gradients, but also prevents the filter from
655 modifying the pixels near detailed regions. Acceptable values are
656 8-32, default value is 16, out-of-range values will be clipped to the
669 Flip the input video horizontally.
671 For example to horizontally flip the video in input with
674 ffmpeg -i in.avi -vf "hflip" out.avi
679 High precision/quality 3d denoise filter. This filter aims to reduce
680 image noise producing smooth images and making still images really
681 still. It should enhance compressibility.
683 It accepts the following optional parameters:
684 @var{luma_spatial}:@var{chroma_spatial}:@var{luma_tmp}:@var{chroma_tmp}
688 a non-negative float number which specifies spatial luma strength,
692 a non-negative float number which specifies spatial chroma strength,
693 defaults to 3.0*@var{luma_spatial}/4.0
696 a float number which specifies luma temporal strength, defaults to
697 6.0*@var{luma_spatial}/4.0
700 a float number which specifies chroma temporal strength, defaults to
701 @var{luma_tmp}*@var{chroma_spatial}/@var{luma_spatial}
704 @section lut, lutrgb, lutyuv
706 Compute a look-up table for binding each pixel component input value
707 to an output value, and apply it to input video.
709 @var{lutyuv} applies a lookup table to a YUV input video, @var{lutrgb}
710 to an RGB input video.
712 These filters accept in input a ":"-separated list of options, which
713 specify the expressions used for computing the lookup table for the
714 corresponding pixel component values.
716 The @var{lut} filter requires either YUV or RGB pixel formats in
717 input, and accepts the options:
719 @var{c0} (first pixel component)
720 @var{c1} (second pixel component)
721 @var{c2} (third pixel component)
722 @var{c3} (fourth pixel component, corresponds to the alpha component)
725 The exact component associated to each option depends on the format in
728 The @var{lutrgb} filter requires RGB pixel formats in input, and
731 @var{r} (red component)
732 @var{g} (green component)
733 @var{b} (blue component)
734 @var{a} (alpha component)
737 The @var{lutyuv} filter requires YUV pixel formats in input, and
740 @var{y} (Y/luminance component)
741 @var{u} (U/Cb component)
742 @var{v} (V/Cr component)
743 @var{a} (alpha component)
746 The expressions can contain the following constants and functions:
750 the corresponding mathematical approximated values for e
751 (euler number), pi (greek PI), PHI (golden ratio)
754 the input width and heigth
757 input value for the pixel component
760 the input value clipped in the @var{minval}-@var{maxval} range
763 maximum value for the pixel component
766 minimum value for the pixel component
769 the negated value for the pixel component value clipped in the
770 @var{minval}-@var{maxval} range , it corresponds to the expression
771 "maxval-clipval+minval"
774 the computed value in @var{val} clipped in the
775 @var{minval}-@var{maxval} range
777 @item gammaval(gamma)
778 the computed gamma correction value of the pixel component value
779 clipped in the @var{minval}-@var{maxval} range, corresponds to the
781 "pow((clipval-minval)/(maxval-minval)\,@var{gamma})*(maxval-minval)+minval"
785 All expressions default to "val".
787 Some examples follow:
790 lutrgb="r=maxval+minval-val:g=maxval+minval-val:b=maxval+minval-val"
791 lutyuv="y=maxval+minval-val:u=maxval+minval-val:v=maxval+minval-val"
793 # the above is the same as
794 lutrgb="r=negval:g=negval:b=negval"
795 lutyuv="y=negval:u=negval:v=negval"
800 # remove chroma components, turns the video into a graytone image
803 # apply a luma burning effect
806 # remove green and blue components
809 # set a constant alpha channel value on input
810 format=rgba,lutrgb=a="maxval-minval/2"
812 # correct luminance gamma by a 0.5 factor
813 lutyuv=y=gammaval(0.5)
818 Apply an MPlayer filter to the input video.
820 This filter provides a wrapper around most of the filters of
823 This wrapper is considered experimental. Some of the wrapped filters
824 may not work properly and we may drop support for them, as they will
825 be implemented natively into FFmpeg. Thus you should avoid
826 depending on them when writing portable scripts.
828 The filters accepts the parameters:
829 @var{filter_name}[:=]@var{filter_params}
831 @var{filter_name} is the name of a supported MPlayer filter,
832 @var{filter_params} is a string containing the parameters accepted by
835 The list of the currently supported filters follows:
896 The parameter syntax and behavior for the listed filters are the same
897 of the corresponding MPlayer filters. For detailed instructions check
898 the "VIDEO FILTERS" section in the MPlayer manual.
900 Some examples follow:
902 # remove a logo by interpolating the surrounding pixels
903 mp=delogo=200:200:80:20:1
905 # adjust gamma, brightness, contrast
908 # tweak hue and saturation
912 See also mplayer(1), @url{http://www.mplayerhq.hu/}.
918 This filter accepts an integer in input, if non-zero it negates the
919 alpha component (if available). The default value in input is 0.
923 Force libavfilter not to use any of the specified pixel formats for the
924 input to the next filter.
926 The filter accepts a list of pixel format names, separated by ":",
927 for example "yuv420p:monow:rgb24".
929 Some examples follow:
931 # force libavfilter to use a format different from "yuv420p" for the
932 # input to the vflip filter
933 noformat=yuv420p,vflip
935 # convert the input video to any of the formats not contained in the list
936 noformat=yuv420p:yuv444p:yuv410p
941 Pass the video source unchanged to the output.
945 Apply video transform using libopencv.
947 To enable this filter install libopencv library and headers and
948 configure FFmpeg with --enable-libopencv.
950 The filter takes the parameters: @var{filter_name}@{:=@}@var{filter_params}.
952 @var{filter_name} is the name of the libopencv filter to apply.
954 @var{filter_params} specifies the parameters to pass to the libopencv
955 filter. If not specified the default values are assumed.
957 Refer to the official libopencv documentation for more precise
959 @url{http://opencv.willowgarage.com/documentation/c/image_filtering.html}
961 Follows the list of supported libopencv filters.
966 Dilate an image by using a specific structuring element.
967 This filter corresponds to the libopencv function @code{cvDilate}.
969 It accepts the parameters: @var{struct_el}:@var{nb_iterations}.
971 @var{struct_el} represents a structuring element, and has the syntax:
972 @var{cols}x@var{rows}+@var{anchor_x}x@var{anchor_y}/@var{shape}
974 @var{cols} and @var{rows} represent the number of colums and rows of
975 the structuring element, @var{anchor_x} and @var{anchor_y} the anchor
976 point, and @var{shape} the shape for the structuring element, and
977 can be one of the values "rect", "cross", "ellipse", "custom".
979 If the value for @var{shape} is "custom", it must be followed by a
980 string of the form "=@var{filename}". The file with name
981 @var{filename} is assumed to represent a binary image, with each
982 printable character corresponding to a bright pixel. When a custom
983 @var{shape} is used, @var{cols} and @var{rows} are ignored, the number
984 or columns and rows of the read file are assumed instead.
986 The default value for @var{struct_el} is "3x3+0x0/rect".
988 @var{nb_iterations} specifies the number of times the transform is
989 applied to the image, and defaults to 1.
993 # use the default values
996 # dilate using a structuring element with a 5x5 cross, iterate two times
997 ocv=dilate=5x5+2x2/cross:2
999 # read the shape from the file diamond.shape, iterate two times
1000 # the file diamond.shape may contain a pattern of characters like this:
1006 # the specified cols and rows are ignored (but not the anchor point coordinates)
1007 ocv=0x0+2x2/custom=diamond.shape:2
1012 Erode an image by using a specific structuring element.
1013 This filter corresponds to the libopencv function @code{cvErode}.
1015 The filter accepts the parameters: @var{struct_el}:@var{nb_iterations},
1016 with the same meaning and use of those of the dilate filter
1021 Smooth the input video.
1023 The filter takes the following parameters:
1024 @var{type}:@var{param1}:@var{param2}:@var{param3}:@var{param4}.
1026 @var{type} is the type of smooth filter to apply, and can be one of
1027 the following values: "blur", "blur_no_scale", "median", "gaussian",
1028 "bilateral". The default value is "gaussian".
1030 @var{param1}, @var{param2}, @var{param3}, and @var{param4} are
1031 parameters whose meanings depend on smooth type. @var{param1} and
1032 @var{param2} accept integer positive values or 0, @var{param3} and
1033 @var{param4} accept float values.
1035 The default value for @var{param1} is 3, the default value for the
1036 other parameters is 0.
1038 These parameters correspond to the parameters assigned to the
1039 libopencv function @code{cvSmooth}.
1043 Overlay one video on top of another.
1045 It takes two inputs and one output, the first input is the "main"
1046 video on which the second input is overlayed.
1048 It accepts the parameters: @var{x}:@var{y}.
1050 @var{x} is the x coordinate of the overlayed video on the main video,
1051 @var{y} is the y coordinate. The parameters are expressions containing
1052 the following parameters:
1055 @item main_w, main_h
1056 main input width and height
1059 same as @var{main_w} and @var{main_h}
1061 @item overlay_w, overlay_h
1062 overlay input width and height
1065 same as @var{overlay_w} and @var{overlay_h}
1068 Be aware that frames are taken from each input video in timestamp
1069 order, hence, if their initial timestamps differ, it is a a good idea
1070 to pass the two inputs through a @var{setpts=PTS-STARTPTS} filter to
1071 have them begin in the same zero timestamp, as it does the example for
1072 the @var{movie} filter.
1074 Follow some examples:
1076 # draw the overlay at 10 pixels from the bottom right
1077 # corner of the main video.
1078 overlay=main_w-overlay_w-10:main_h-overlay_h-10
1080 # insert a transparent PNG logo in the bottom left corner of the input
1081 movie=logo.png [logo];
1082 [in][logo] overlay=10:main_h-overlay_h-10 [out]
1084 # insert 2 different transparent PNG logos (second logo on bottom
1086 movie=logo1.png [logo1];
1087 movie=logo2.png [logo2];
1088 [in][logo1] overlay=10:H-h-10 [in+logo1];
1089 [in+logo1][logo2] overlay=W-w-10:H-h-10 [out]
1091 # add a transparent color layer on top of the main video,
1092 # WxH specifies the size of the main input to the overlay filter
1093 color=red@.3:WxH [over]; [in][over] overlay [out]
1096 You can chain togheter more overlays but the efficiency of such
1097 approach is yet to be tested.
1101 Add paddings to the input image, and places the original input at the
1102 given coordinates @var{x}, @var{y}.
1104 It accepts the following parameters:
1105 @var{width}:@var{height}:@var{x}:@var{y}:@var{color}.
1107 The parameters @var{width}, @var{height}, @var{x}, and @var{y} are
1108 expressions containing the following constants:
1112 the corresponding mathematical approximated values for e
1113 (euler number), pi (greek PI), phi (golden ratio)
1116 the input video width and heigth
1119 same as @var{in_w} and @var{in_h}
1122 the output width and heigth, that is the size of the padded area as
1123 specified by the @var{width} and @var{height} expressions
1126 same as @var{out_w} and @var{out_h}
1129 x and y offsets as specified by the @var{x} and @var{y}
1130 expressions, or NAN if not yet specified
1133 input display aspect ratio, same as @var{iw} / @var{ih}
1136 horizontal and vertical chroma subsample values. For example for the
1137 pixel format "yuv422p" @var{hsub} is 2 and @var{vsub} is 1.
1140 Follows the description of the accepted parameters.
1145 Specify the size of the output image with the paddings added. If the
1146 value for @var{width} or @var{height} is 0, the corresponding input size
1147 is used for the output.
1149 The @var{width} expression can reference the value set by the
1150 @var{height} expression, and viceversa.
1152 The default value of @var{width} and @var{height} is 0.
1156 Specify the offsets where to place the input image in the padded area
1157 with respect to the top/left border of the output image.
1159 The @var{x} expression can reference the value set by the @var{y}
1160 expression, and viceversa.
1162 The default value of @var{x} and @var{y} is 0.
1166 Specify the color of the padded area, it can be the name of a color
1167 (case insensitive match) or a 0xRRGGBB[AA] sequence.
1169 The default value of @var{color} is "black".
1173 Some examples follow:
1176 # Add paddings with color "violet" to the input video. Output video
1177 # size is 640x480, the top-left corner of the input video is placed at
1179 pad=640:480:0:40:violet
1181 # pad the input to get an output with dimensions increased bt 3/2,
1182 # and put the input video at the center of the padded area
1183 pad="3/2*iw:3/2*ih:(ow-iw)/2:(oh-ih)/2"
1185 # pad the input to get a squared output with size equal to the maximum
1186 # value between the input width and height, and put the input video at
1187 # the center of the padded area
1188 pad="max(iw\,ih):ow:(ow-iw)/2:(oh-ih)/2"
1190 # pad the input to get a final w/h ratio of 16:9
1191 pad="ih*16/9:ih:(ow-iw)/2:(oh-ih)/2"
1193 # double output size and put the input video in the bottom-right
1194 # corner of the output padded area
1195 pad="2*iw:2*ih:ow-iw:oh-ih"
1198 @section pixdesctest
1200 Pixel format descriptor test filter, mainly useful for internal
1201 testing. The output video should be equal to the input video.
1205 format=monow, pixdesctest
1208 can be used to test the monowhite pixel format descriptor definition.
1212 Scale the input video to @var{width}:@var{height} and/or convert the image format.
1214 The parameters @var{width} and @var{height} are expressions containing
1215 the following constants:
1219 the corresponding mathematical approximated values for e
1220 (euler number), pi (greek PI), phi (golden ratio)
1223 the input width and heigth
1226 same as @var{in_w} and @var{in_h}
1229 the output (cropped) width and heigth
1232 same as @var{out_w} and @var{out_h}
1235 input display aspect ratio, same as @var{iw} / @var{ih}
1238 horizontal and vertical chroma subsample values. For example for the
1239 pixel format "yuv422p" @var{hsub} is 2 and @var{vsub} is 1.
1242 If the input image format is different from the format requested by
1243 the next filter, the scale filter will convert the input to the
1246 If the value for @var{width} or @var{height} is 0, the respective input
1247 size is used for the output.
1249 If the value for @var{width} or @var{height} is -1, the scale filter will
1250 use, for the respective output size, a value that maintains the aspect
1251 ratio of the input image.
1253 The default value of @var{width} and @var{height} is 0.
1255 Some examples follow:
1257 # scale the input video to a size of 200x100.
1260 # scale the input to 2x
1262 # the above is the same as
1265 # scale the input to half size
1268 # increase the width, and set the height to the same size
1271 # seek for Greek harmony
1275 # increase the height, and set the width to 3/2 of the height
1278 # increase the size, but make the size a multiple of the chroma
1279 scale="trunc(3/2*iw/hsub)*hsub:trunc(3/2*ih/vsub)*vsub"
1281 # increase the width to a maximum of 500 pixels, keep the same input aspect ratio
1282 scale='min(500\, iw*3/2):-1'
1286 Select frames to pass in output.
1288 It accepts in input an expression, which is evaluated for each input
1289 frame. If the expression is evaluated to a non-zero value, the frame
1290 is selected and passed to the output, otherwise it is discarded.
1292 The expression can contain the following constants:
1305 the sequential number of the filtered frame, starting from 0
1308 the sequential number of the selected frame, starting from 0
1310 @item prev_selected_n
1311 the sequential number of the last selected frame, NAN if undefined
1314 timebase of the input timestamps
1317 the PTS (Presentation TimeStamp) of the filtered video frame,
1318 expressed in @var{TB} units, NAN if undefined
1321 the PTS (Presentation TimeStamp) of the filtered video frame,
1322 expressed in seconds, NAN if undefined
1325 the PTS of the previously filtered video frame, NAN if undefined
1327 @item prev_selected_pts
1328 the PTS of the last previously filtered video frame, NAN if undefined
1330 @item prev_selected_t
1331 the PTS of the last previously selected video frame, NAN if undefined
1334 the PTS of the first video frame in the video, NAN if undefined
1337 the time of the first video frame in the video, NAN if undefined
1340 the picture type of the filtered frame, can assume one of the following
1352 @item interlace_type
1353 the frame interlace type, can assume one of the following values:
1355 @item INTERLACE_TYPE_P
1356 the frame is progressive (not interlaced)
1357 @item INTERLACE_TYPE_T
1358 the frame is top-field-first
1359 @item INTERLACE_TYPE_B
1360 the frame is bottom-field-first
1364 1 if the filtered frame is a key-frame, 0 otherwise
1367 the position in the file of the filtered frame, -1 if the information
1368 is not available (e.g. for synthetic video)
1371 The default value of the select expression is "1".
1373 Some examples follow:
1376 # select all frames in input
1379 # the above is the same as:
1385 # select only I-frames
1386 select='eq(pict_type\,PICT_TYPE_I)'
1388 # select one frame every 100
1389 select='not(mod(n\,100))'
1391 # select only frames contained in the 10-20 time interval
1392 select='gte(t\,10)*lte(t\,20)'
1394 # select only I frames contained in the 10-20 time interval
1395 select='gte(t\,10)*lte(t\,20)*eq(pict_type\,PICT_TYPE_I)'
1397 # select frames with a minimum distance of 10 seconds
1398 select='isnan(prev_selected_t)+gte(t-prev_selected_t\,10)'
1404 Set the Display Aspect Ratio for the filter output video.
1406 This is done by changing the specified Sample (aka Pixel) Aspect
1407 Ratio, according to the following equation:
1408 @math{DAR = HORIZONTAL_RESOLUTION / VERTICAL_RESOLUTION * SAR}
1410 Keep in mind that this filter does not modify the pixel dimensions of
1411 the video frame. Also the display aspect ratio set by this filter may
1412 be changed by later filters in the filterchain, e.g. in case of
1413 scaling or if another "setdar" or a "setsar" filter is applied.
1415 The filter accepts a parameter string which represents the wanted
1416 display aspect ratio.
1417 The parameter can be a floating point number string, or an expression
1418 of the form @var{num}:@var{den}, where @var{num} and @var{den} are the
1419 numerator and denominator of the aspect ratio.
1420 If the parameter is not specified, it is assumed the value "0:1".
1422 For example to change the display aspect ratio to 16:9, specify:
1425 # the above is equivalent to
1429 See also the "setsar" filter documentation (@pxref{setsar}).
1433 Change the PTS (presentation timestamp) of the input video frames.
1435 Accept in input an expression evaluated through the eval API, which
1436 can contain the following constants:
1440 the presentation timestamp in input
1452 the count of the input frame, starting from 0.
1455 the PTS of the first video frame
1458 tell if the current frame is interlaced
1461 original position in the file of the frame, or undefined if undefined
1462 for the current frame
1472 Some examples follow:
1475 # start counting PTS from zero
1487 # fixed rate 25 fps with some jitter
1488 setpts='1/(25*TB) * (N + 0.05 * sin(N*2*PI/25))'
1494 Set the Sample (aka Pixel) Aspect Ratio for the filter output video.
1496 Note that as a consequence of the application of this filter, the
1497 output display aspect ratio will change according to the following
1499 @math{DAR = HORIZONTAL_RESOLUTION / VERTICAL_RESOLUTION * SAR}
1501 Keep in mind that the sample aspect ratio set by this filter may be
1502 changed by later filters in the filterchain, e.g. if another "setsar"
1503 or a "setdar" filter is applied.
1505 The filter accepts a parameter string which represents the wanted
1506 sample aspect ratio.
1507 The parameter can be a floating point number string, or an expression
1508 of the form @var{num}:@var{den}, where @var{num} and @var{den} are the
1509 numerator and denominator of the aspect ratio.
1510 If the parameter is not specified, it is assumed the value "0:1".
1512 For example to change the sample aspect ratio to 10:11, specify:
1519 Set the timebase to use for the output frames timestamps.
1520 It is mainly useful for testing timebase configuration.
1522 It accepts in input an arithmetic expression representing a rational.
1523 The expression can contain the constants "PI", "E", "PHI", "AVTB" (the
1524 default timebase), and "intb" (the input timebase).
1526 The default value for the input is "intb".
1528 Follow some examples.
1531 # set the timebase to 1/25
1534 # set the timebase to 1/10
1537 #set the timebase to 1001/1000
1540 #set the timebase to 2*intb
1543 #set the default timebase value
1549 Show a line containing various information for each input video frame.
1550 The input video is not modified.
1552 The shown line contains a sequence of key/value pairs of the form
1553 @var{key}:@var{value}.
1555 A description of each shown parameter follows:
1559 sequential number of the input frame, starting from 0
1562 Presentation TimeStamp of the input frame, expressed as a number of
1563 time base units. The time base unit depends on the filter input pad.
1566 Presentation TimeStamp of the input frame, expressed as a number of
1570 position of the frame in the input stream, -1 if this information in
1571 unavailable and/or meanigless (for example in case of synthetic video)
1577 sample aspect ratio of the input frame, expressed in the form
1581 size of the input frame, expressed in the form
1582 @var{width}x@var{height}
1585 interlaced mode ("P" for "progressive", "T" for top field first, "B"
1586 for bottom field first)
1589 1 if the frame is a key frame, 0 otherwise
1592 picture type of the input frame ("I" for an I-frame, "P" for a
1593 P-frame, "B" for a B-frame, "?" for unknown type).
1594 Check also the documentation of the @code{AVPictureType} enum and of
1595 the @code{av_get_picture_type_char} function defined in
1596 @file{libavutil/avutil.h}.
1599 Adler-32 checksum of all the planes of the input frame
1601 @item plane_checksum
1602 Adler-32 checksum of each plane of the input frame, expressed in the form
1603 "[@var{c0} @var{c1} @var{c2} @var{c3}]"
1608 Pass the images of input video on to next video filter as multiple
1612 ./ffmpeg -i in.avi -vf "slicify=32" out.avi
1615 The filter accepts the slice height as parameter. If the parameter is
1616 not specified it will use the default value of 16.
1618 Adding this in the beginning of filter chains should make filtering
1619 faster due to better use of the memory cache.
1623 Pass on the input video to two outputs. Both outputs are identical to
1628 [in] split [splitout1][splitout2];
1629 [splitout1] crop=100:100:0:0 [cropout];
1630 [splitout2] pad=200:200:100:100 [padout];
1633 will create two separate outputs from the same input, one cropped and
1638 Transpose rows with columns in the input video and optionally flip it.
1640 It accepts a parameter representing an integer, which can assume the
1645 Rotate by 90 degrees counterclockwise and vertically flip (default), that is:
1653 Rotate by 90 degrees clockwise, that is:
1661 Rotate by 90 degrees counterclockwise, that is:
1669 Rotate by 90 degrees clockwise and vertically flip, that is:
1679 Sharpen or blur the input video.
1681 It accepts the following parameters:
1682 @var{luma_msize_x}:@var{luma_msize_y}:@var{luma_amount}:@var{chroma_msize_x}:@var{chroma_msize_y}:@var{chroma_amount}
1684 Negative values for the amount will blur the input video, while positive
1685 values will sharpen. All parameters are optional and default to the
1686 equivalent of the string '5:5:1.0:0:0:0.0'.
1691 Set the luma matrix horizontal size. It can be an integer between 3
1692 and 13, default value is 5.
1695 Set the luma matrix vertical size. It can be an integer between 3
1696 and 13, default value is 5.
1699 Set the luma effect strength. It can be a float number between -2.0
1700 and 5.0, default value is 1.0.
1702 @item chroma_msize_x
1703 Set the chroma matrix horizontal size. It can be an integer between 3
1704 and 13, default value is 0.
1706 @item chroma_msize_y
1707 Set the chroma matrix vertical size. It can be an integer between 3
1708 and 13, default value is 0.
1711 Set the chroma effect strength. It can be a float number between -2.0
1712 and 5.0, default value is 0.0.
1717 # Strong luma sharpen effect parameters
1720 # Strong blur of both luma and chroma parameters
1721 unsharp=7:7:-2:7:7:-2
1723 # Use the default values with @command{ffmpeg}
1724 ./ffmpeg -i in.avi -vf "unsharp" out.mp4
1729 Flip the input video vertically.
1732 ./ffmpeg -i in.avi -vf "vflip" out.avi
1737 Deinterlace the input video ("yadif" means "yet another deinterlacing
1740 It accepts the optional parameters: @var{mode}:@var{parity}.
1742 @var{mode} specifies the interlacing mode to adopt, accepts one of the
1747 output 1 frame for each frame
1749 output 1 frame for each field
1751 like 0 but skips spatial interlacing check
1753 like 1 but skips spatial interlacing check
1758 @var{parity} specifies the picture field parity assumed for the input
1759 interlaced video, accepts one of the following values:
1763 assume bottom field first
1765 assume top field first
1767 enable automatic detection
1770 Default value is -1.
1771 If interlacing is unknown or decoder does not export this information,
1772 top field first will be assumed.
1774 @c man end VIDEO FILTERS
1776 @chapter Video Sources
1777 @c man begin VIDEO SOURCES
1779 Below is a description of the currently available video sources.
1783 Buffer video frames, and make them available to the filter chain.
1785 This source is mainly intended for a programmatic use, in particular
1786 through the interface defined in @file{libavfilter/vsrc_buffer.h}.
1788 It accepts the following parameters:
1789 @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}
1791 All the parameters but @var{scale_params} need to be explicitely
1794 Follows the list of the accepted parameters.
1799 Specify the width and height of the buffered video frames.
1801 @item pix_fmt_string
1802 A string representing the pixel format of the buffered video frames.
1803 It may be a number corresponding to a pixel format, or a pixel format
1806 @item timebase_num, timebase_den
1807 Specify numerator and denomitor of the timebase assumed by the
1808 timestamps of the buffered frames.
1810 @item sample_aspect_ratio.num, sample_aspect_ratio.den
1811 Specify numerator and denominator of the sample aspect ratio assumed
1812 by the video frames.
1815 Specify the optional parameters to be used for the scale filter which
1816 is automatically inserted when an input change is detected in the
1817 input size or format.
1822 buffer=320:240:yuv410p:1:24:1:1
1825 will instruct the source to accept video frames with size 320x240 and
1826 with format "yuv410p", assuming 1/24 as the timestamps timebase and
1827 square pixels (1:1 sample aspect ratio).
1828 Since the pixel format with name "yuv410p" corresponds to the number 6
1829 (check the enum PixelFormat definition in @file{libavutil/pixfmt.h}),
1830 this example corresponds to:
1832 buffer=320:240:6:1:24:1:1
1837 Provide an uniformly colored input.
1839 It accepts the following parameters:
1840 @var{color}:@var{frame_size}:@var{frame_rate}
1842 Follows the description of the accepted parameters.
1847 Specify the color of the source. It can be the name of a color (case
1848 insensitive match) or a 0xRRGGBB[AA] sequence, possibly followed by an
1849 alpha specifier. The default value is "black".
1852 Specify the size of the sourced video, it may be a string of the form
1853 @var{width}x@var{heigth}, or the name of a size abbreviation. The
1854 default value is "320x240".
1857 Specify the frame rate of the sourced video, as the number of frames
1858 generated per second. It has to be a string in the format
1859 @var{frame_rate_num}/@var{frame_rate_den}, an integer number, a float
1860 number or a valid video frame rate abbreviation. The default value is
1865 For example the following graph description will generate a red source
1866 with an opacity of 0.2, with size "qcif" and a frame rate of 10
1867 frames per second, which will be overlayed over the source connected
1868 to the pad with identifier "in".
1871 "color=red@@0.2:qcif:10 [color]; [in][color] overlay [out]"
1876 Read a video stream from a movie container.
1878 It accepts the syntax: @var{movie_name}[:@var{options}] where
1879 @var{movie_name} is the name of the resource to read (not necessarily
1880 a file but also a device or a stream accessed through some protocol),
1881 and @var{options} is an optional sequence of @var{key}=@var{value}
1882 pairs, separated by ":".
1884 The description of the accepted options follows.
1888 @item format_name, f
1889 Specifies the format assumed for the movie to read, and can be either
1890 the name of a container or an input device. If not specified the
1891 format is guessed from @var{movie_name} or by probing.
1893 @item seek_point, sp
1894 Specifies the seek point in seconds, the frames will be output
1895 starting from this seek point, the parameter is evaluated with
1896 @code{av_strtod} so the numerical value may be suffixed by an IS
1897 postfix. Default value is "0".
1899 @item stream_index, si
1900 Specifies the index of the video stream to read. If the value is -1,
1901 the best suited video stream will be automatically selected. Default
1906 This filter allows to overlay a second video on top of main input of
1907 a filtergraph as shown in this graph:
1909 input -----------> deltapts0 --> overlay --> output
1912 movie --> scale--> deltapts1 -------+
1915 Some examples follow:
1917 # skip 3.2 seconds from the start of the avi file in.avi, and overlay it
1918 # on top of the input labelled as "in".
1919 movie=in.avi:seek_point=3.2, scale=180:-1, setpts=PTS-STARTPTS [movie];
1920 [in] setpts=PTS-STARTPTS, [movie] overlay=16:16 [out]
1922 # read from a video4linux2 device, and overlay it on top of the input
1924 movie=/dev/video0:f=video4linux2, scale=180:-1, setpts=PTS-STARTPTS [movie];
1925 [in] setpts=PTS-STARTPTS, [movie] overlay=16:16 [out]
1931 Null video source, never return images. It is mainly useful as a
1932 template and to be employed in analysis / debugging tools.
1934 It accepts as optional parameter a string of the form
1935 @var{width}:@var{height}:@var{timebase}.
1937 @var{width} and @var{height} specify the size of the configured
1938 source. The default values of @var{width} and @var{height} are
1939 respectively 352 and 288 (corresponding to the CIF size format).
1941 @var{timebase} specifies an arithmetic expression representing a
1942 timebase. The expression can contain the constants "PI", "E", "PHI",
1943 "AVTB" (the default timebase), and defaults to the value "AVTB".
1947 Provide a frei0r source.
1949 To enable compilation of this filter you need to install the frei0r
1950 header and configure FFmpeg with --enable-frei0r.
1952 The source supports the syntax:
1954 @var{size}:@var{rate}:@var{src_name}[@{=|:@}@var{param1}:@var{param2}:...:@var{paramN}]
1957 @var{size} is the size of the video to generate, may be a string of the
1958 form @var{width}x@var{height} or a frame size abbreviation.
1959 @var{rate} is the rate of the video to generate, may be a string of
1960 the form @var{num}/@var{den} or a frame rate abbreviation.
1961 @var{src_name} is the name to the frei0r source to load. For more
1962 information regarding frei0r and how to set the parameters read the
1963 section "frei0r" (@pxref{frei0r}) in the description of the video
1966 Some examples follow:
1968 # generate a frei0r partik0l source with size 200x200 and framerate 10
1969 # which is overlayed on the overlay filter main input
1970 frei0r_src=200x200:10:partik0l=1234 [overlay]; [in][overlay] overlay
1973 @c man end VIDEO SOURCES
1975 @chapter Video Sinks
1976 @c man begin VIDEO SINKS
1978 Below is a description of the currently available video sinks.
1982 Buffer video frames, and make them available to the end of the filter
1985 This sink is mainly intended for a programmatic use, in particular
1986 through the interface defined in @file{libavfilter/vsink_buffer.h}.
1988 It does not require a string parameter in input, but you need to
1989 specify a pointer to a list of supported pixel formats terminated by
1990 -1 in the opaque parameter provided to @code{avfilter_init_filter}
1991 when initializing this sink.
1995 Null video sink, do absolutely nothing with the input video. It is
1996 mainly useful as a template and to be employed in analysis / debugging
1999 @c man end VIDEO SINKS