Below is a description of the currently available audio filters.
+@section acompressor
+
+A compressor is mainly used to reduce the dynamic range of a signal.
+Especially modern music is mostly compressed at a high ratio to
+improve the overall loudness. It's done to get the highest attention
+of a listener, "fatten" the sound and bring more "power" to the track.
+If a signal is compressed too much it may sound dull or "dead"
+afterwards or it may start to "pump" (which could be a powerful effect
+but can also destroy a track completely).
+The right compression is the key to reach a professional sound and is
+the high art of mixing and mastering. Because of its complex settings
+it may take a long time to get the right feeling for this kind of effect.
+
+Compression is done by detecting the volume above a chosen level
+@code{threshold} and dividing it by the factor set with @code{ratio}.
+So if you set the threshold to -12dB and your signal reaches -6dB a ratio
+of 2:1 will result in a signal at -9dB. Because an exact manipulation of
+the signal would cause distortion of the waveform the reduction can be
+levelled over the time. This is done by setting "Attack" and "Release".
+@code{attack} determines how long the signal has to rise above the threshold
+before any reduction will occur and @code{release} sets the time the signal
+has to fall below the threshold to reduce the reduction again. Shorter signals
+than the chosen attack time will be left untouched.
+The overall reduction of the signal can be made up afterwards with the
+@code{makeup} setting. So compressing the peaks of a signal about 6dB and
+raising the makeup to this level results in a signal twice as loud than the
+source. To gain a softer entry in the compression the @code{knee} flattens the
+hard edge at the threshold in the range of the chosen decibels.
+
+The filter accepts the following options:
+
+@table @option
+@item level_in
+Set input gain. Default is 1. Range is between 0.015625 and 64.
+
+@item threshold
+If a signal of second stream rises above this level it will affect the gain
+reduction of the first stream.
+By default it is 0.125. Range is between 0.00097563 and 1.
+
+@item ratio
+Set a ratio by which the signal is reduced. 1:2 means that if the level
+rose 4dB above the threshold, it will be only 2dB above after the reduction.
+Default is 2. Range is between 1 and 20.
+
+@item attack
+Amount of milliseconds the signal has to rise above the threshold before gain
+reduction starts. Default is 20. Range is between 0.01 and 2000.
+
+@item release
+Amount of milliseconds the signal has to fall below the threshold before
+reduction is decreased again. Default is 250. Range is between 0.01 and 9000.
+
+@item makeup
+Set the amount by how much signal will be amplified after processing.
+Default is 2. Range is from 1 and 64.
+
+@item knee
+Curve the sharp knee around the threshold to enter gain reduction more softly.
+Default is 2.82843. Range is between 1 and 8.
+
+@item link
+Choose if the @code{average} level between all channels of input stream
+or the louder(@code{maximum}) channel of input stream affects the
+reduction. Default is @code{average}.
+
+@item detection
+Should the exact signal be taken in case of @code{peak} or an RMS one in case
+of @code{rms}. Default is @code{rms} which is mostly smoother.
+
+@item mix
+How much to use compressed signal in output. Default is 1.
+Range is between 0 and 1.
+@end table
+
@section acrossfade
Apply cross fade from one input audio stream to another input audio stream.
@end example
@end itemize
+@section aemphasis
+Audio emphasis filter creates or restores material directly taken from LPs or
+emphased CDs with different filter curves. E.g. to store music on vinyl the
+signal has to be altered by a filter first to even out the disadvantages of
+this recording medium.
+Once the material is played back the inverse filter has to be applied to
+restore the distortion of the frequency response.
+
+The filter accepts the following options:
+
+@table @option
+@item level_in
+Set input gain.
+
+@item level_out
+Set output gain.
+
+@item mode
+Set filter mode. For restoring material use @code{reproduction} mode, otherwise
+use @code{production} mode. Default is @code{reproduction} mode.
+
+@item type
+Set filter type. Selects medium. Can be one of the following:
+
+@table @option
+@item col
+select Columbia.
+@item emi
+select EMI.
+@item bsi
+select BSI (78RPM).
+@item riaa
+select RIAA.
+@item cd
+select Compact Disc (CD).
+@item 50fm
+select 50µs (FM).
+@item 75fm
+select 75µs (FM).
+@item 50kf
+select 50µs (FM-KF).
+@item 75kf
+select 75µs (FM-KF).
+@end table
+@end table
+
@section aeval
Modify an audio signal according to the specified expressions.
@table @option
@item level_in
Set input level before filtering.
+Default is 1. Allowed range is from 0.015625 to 64.
@item range
Set the level of gain reduction when the signal is below the threshold.
+Default is 0.06125. Allowed range is from 0 to 1.
@item threshold
If a signal rises above this level the gain reduction is released.
+Default is 0.125. Allowed range is from 0 to 1.
@item ratio
Set a ratio about which the signal is reduced.
+Default is 2. Allowed range is from 1 to 9000.
@item attack
Amount of milliseconds the signal has to rise above the threshold before gain
reduction stops.
+Default is 20 milliseconds. Allowed range is from 0.01 to 9000.
@item release
Amount of milliseconds the signal has to fall below the threshold before the
-reduction is increased again.
+reduction is increased again. Default is 250 milliseconds.
+Allowed range is from 0.01 to 9000.
@item makeup
Set amount of amplification of signal after processing.
+Default is 1. Allowed range is from 1 to 64.
@item knee
Curve the sharp knee around the threshold to enter gain reduction more softly.
+Default is 2.828427125. Allowed range is from 1 to 8.
@item detection
Choose if exact signal should be taken for detection or an RMS like one.
+Default is rms. Can be peak or rms.
@item link
Choose if the average level between all channels or the louder channel affects
the reduction.
+Default is average. Can be average or maximum.
@end table
@section alimiter
@end table
@end table
+@section apulsator
+
+Audio pulsator is something between an autopanner and a tremolo.
+But it can produce funny stereo effects as well. Pulsator changes the volume
+of the left and right channel based on a LFO (low frequency oscillator) with
+different waveforms and shifted phases.
+This filter have the ability to define an offset between left and right
+channel. An offset of 0 means that both LFO shapes match each other.
+The left and right channel are altered equally - a conventional tremolo.
+An offset of 50% means that the shape of the right channel is exactly shifted
+in phase (or moved backwards about half of the frequency) - pulsator acts as
+an autopanner. At 1 both curves match again. Every setting in between moves the
+phase shift gapless between all stages and produces some "bypassing" sounds with
+sine and triangle waveforms. The more you set the offset near 1 (starting from
+the 0.5) the faster the signal passes from the left to the right speaker.
+
+The filter accepts the following options:
+
+@table @option
+@item level_in
+Set input gain. By default it is 1. Range is [0.015625 - 64].
+
+@item level_out
+Set output gain. By default it is 1. Range is [0.015625 - 64].
+
+@item mode
+Set waveform shape the LFO will use. Can be one of: sine, triangle, square,
+sawup or sawdown. Default is sine.
+
+@item amount
+Set modulation. Define how much of original signal is affected by the LFO.
+
+@item offset_l
+Set left channel offset. Default is 0. Allowed range is [0 - 1].
+
+@item offset_r
+Set right channel offset. Default is 0.5. Allowed range is [0 - 1].
+
+@item width
+Set pulse width. Default is 1. Allowed range is [0 - 2].
+
+@item timing
+Set possible timing mode. Can be one of: bpm, ms or hz. Default is hz.
+
+@item bpm
+Set bpm. Default is 120. Allowed range is [30 - 300]. Only used if timing
+is set to bpm.
+
+@item ms
+Set ms. Default is 500. Allowed range is [10 - 2000]. Only used if timing
+is set to ms.
+
+@item hz
+Set frequency in Hz. Default is 2. Allowed range is [0.01 - 100]. Only used
+if timing is set to hz.
+@end table
+
@anchor{aresample}
@section aresample
@end example
@end itemize
+@section compensationdelay
+
+Compensation Delay Line is a metric based delay to compensate differing
+positions of microphones or speakers.
+
+For example, you have recorded guitar with two microphones placed in
+different location. Because the front of sound wave has fixed speed in
+normal conditions, the phasing of microphones can vary and depends on
+their location and interposition. The best sound mix can be achieved when
+these microphones are in phase (synchronized). Note that distance of
+~30 cm between microphones makes one microphone to capture signal in
+antiphase to another microphone. That makes the final mix sounding moody.
+This filter helps to solve phasing problems by adding different delays
+to each microphone track and make them synchronized.
+
+The best result can be reached when you take one track as base and
+synchronize other tracks one by one with it.
+Remember that synchronization/delay tolerance depends on sample rate, too.
+Higher sample rates will give more tolerance.
+
+It accepts the following parameters:
+
+@table @option
+@item mm
+Set millimeters distance. This is compensation distance for fine tuning.
+Default is 0.
+
+@item cm
+Set cm distance. This is compensation distance for tightening distance setup.
+Default is 0.
+
+@item m
+Set meters distance. This is compensation distance for hard distance setup.
+Default is 0.
+
+@item dry
+Set dry amount. Amount of unprocessed (dry) signal.
+Default is 0.
+
+@item wet
+Set wet amount. Amount of processed (wet) signal.
+Default is 1.
+
+@item temp
+Set temperature degree in Celsius. This is the temperature of the environment.
+Default is 20.
+@end table
+
@section dcshift
Apply a DC shift to the audio.
The filter accepts the following options:
@table @option
+@item level_in
+Set input gain. Default is 1. Range is between 0.015625 and 64.
+
@item threshold
If a signal of second stream raises above this level it will affect the gain
reduction of first stream.
@item detection
Should the exact signal be taken in case of @code{peak} or an RMS one in case
of @code{rms}. Default is @code{rms} which is mainly smoother.
+
+@item level_sc
+Set sidechain gain. Default is 1. Range is between 0.015625 and 64.
+
+@item mix
+How much to use compressed signal in output. Default is 1.
+Range is between 0 and 1.
@end table
@subsection Examples
@end example
@end itemize
+@section sidechaingate
+
+A sidechain gate acts like a normal (wideband) gate but has the ability to
+filter the detected signal before sending it to the gain reduction stage.
+Normally a gate uses the full range signal to detect a level above the
+threshold.
+For example: If you cut all lower frequencies from your sidechain signal
+the gate will decrease the volume of your track only if not enough highs
+appear. With this technique you are able to reduce the resonation of a
+natural drum or remove "rumbling" of muted strokes from a heavily distorted
+guitar.
+It needs two input streams and returns one output stream.
+First input stream will be processed depending on second stream signal.
+
+The filter accepts the following options:
+
+@table @option
+@item level_in
+Set input level before filtering.
+Default is 1. Allowed range is from 0.015625 to 64.
+
+@item range
+Set the level of gain reduction when the signal is below the threshold.
+Default is 0.06125. Allowed range is from 0 to 1.
+
+@item threshold
+If a signal rises above this level the gain reduction is released.
+Default is 0.125. Allowed range is from 0 to 1.
+
+@item ratio
+Set a ratio about which the signal is reduced.
+Default is 2. Allowed range is from 1 to 9000.
+
+@item attack
+Amount of milliseconds the signal has to rise above the threshold before gain
+reduction stops.
+Default is 20 milliseconds. Allowed range is from 0.01 to 9000.
+
+@item release
+Amount of milliseconds the signal has to fall below the threshold before the
+reduction is increased again. Default is 250 milliseconds.
+Allowed range is from 0.01 to 9000.
+
+@item makeup
+Set amount of amplification of signal after processing.
+Default is 1. Allowed range is from 1 to 64.
+
+@item knee
+Curve the sharp knee around the threshold to enter gain reduction more softly.
+Default is 2.828427125. Allowed range is from 1 to 8.
+
+@item detection
+Choose if exact signal should be taken for detection or an RMS like one.
+Default is rms. Can be peak or rms.
+
+@item link
+Choose if the average level between all channels or the louder channel affects
+the reduction.
+Default is average. Can be average or maximum.
+
+@item level_sc
+Set sidechain gain. Default is 1. Range is from 0.015625 to 64.
+@end table
+
@section silencedetect
Detect silence in an audio stream.
@item bb
backward predicted MVs of B-frames
@end table
+
+@item qp
+Display quantization parameters using the chroma planes
@end table
@subsection Examples
@item
Show the text at the center of the video frame:
@example
-drawtext="fontsize=30:fontfile=FreeSerif.ttf:text='hello world':x=(w-text_w)/2:y=(h-text_h-line_h)/2"
+drawtext="fontsize=30:fontfile=FreeSerif.ttf:text='hello world':x=(w-text_w)/2:y=(h-text_h)/2"
@end example
@item
ffmpeg -i in.vob -vf "fieldorder=bff" out.dv
@end example
-@section fifo
+@section fifo, afifo
Buffer input images and send them when they are requested.
The computed histogram is a representation of the color component
distribution in an image.
-The filter accepts the following options:
-
-@table @option
-@item mode
-Set histogram mode.
-
-It accepts the following values:
-@table @samp
-@item levels
-Standard histogram that displays the color components distribution in an
-image. Displays color graph for each color component. Shows distribution of
+Standard histogram displays the color components distribution in an image.
+Displays color graph for each color component. Shows distribution of
the Y, U, V, A or R, G, B components, depending on input format, in the
current frame. Below each graph a color component scale meter is shown.
-@item color
-Displays chroma values (U/V color placement) in a two dimensional
-graph (which is called a vectorscope). The brighter a pixel in the
-vectorscope, the more pixels of the input frame correspond to that pixel
-(i.e., more pixels have this chroma value). The V component is displayed on
-the horizontal (X) axis, with the leftmost side being V = 0 and the rightmost
-side being V = 255. The U component is displayed on the vertical (Y) axis,
-with the top representing U = 0 and the bottom representing U = 255.
-
-The position of a white pixel in the graph corresponds to the chroma value of
-a pixel of the input clip. The graph can therefore be used to read the hue
-(color flavor) and the saturation (the dominance of the hue in the color). As
-the hue of a color changes, it moves around the square. At the center of the
-square the saturation is zero, which means that the corresponding pixel has no
-color. If the amount of a specific color is increased (while leaving the other
-colors unchanged) the saturation increases, and the indicator moves towards
-the edge of the square.
-
-@item color2
-Chroma values in vectorscope, similar as @code{color} but actual chroma values
-are displayed.
-
-@item waveform
-Per row/column color component graph. In row mode, the graph on the left side
-represents color component value 0 and the right side represents value = 255.
-In column mode, the top side represents color component value = 0 and bottom
-side represents value = 255.
-@end table
-Default value is @code{levels}.
+The filter accepts the following options:
+@table @option
@item level_height
-Set height of level in @code{levels}. Default value is @code{200}.
+Set height of level. Default value is @code{200}.
Allowed range is [50, 2048].
@item scale_height
-Set height of color scale in @code{levels}. Default value is @code{12}.
+Set height of color scale. Default value is @code{12}.
Allowed range is [0, 40].
-@item step
-Set step for @code{waveform} mode. Smaller values are useful to find out how
-many values of the same luminance are distributed across input rows/columns.
-Default value is @code{10}. Allowed range is [1, 255].
-
-@item waveform_mode
-Set mode for @code{waveform}. Can be either @code{row}, or @code{column}.
-Default is @code{row}.
-
-@item waveform_mirror
-Set mirroring mode for @code{waveform}. @code{0} means unmirrored, @code{1}
-means mirrored. In mirrored mode, higher values will be represented on the left
-side for @code{row} mode and at the top for @code{column} mode. Default is
-@code{0} (unmirrored).
-
@item display_mode
-Set display mode for @code{waveform} and @code{levels}.
+Set display mode.
It accepts the following values:
@table @samp
@item parade
-Display separate graph for the color components side by side in
-@code{row} waveform mode or one below the other in @code{column} waveform mode
-for @code{waveform} histogram mode. For @code{levels} histogram mode,
-per color component graphs are placed below each other.
-
-Using this display mode in @code{waveform} histogram mode makes it easy to
-spot color casts in the highlights and shadows of an image, by comparing the
-contours of the top and the bottom graphs of each waveform. Since whites,
-grays, and blacks are characterized by exactly equal amounts of red, green,
-and blue, neutral areas of the picture should display three waveforms of
-roughly equal width/height. If not, the correction is easy to perform by
-making level adjustments the three waveforms.
+Per color component graphs are placed below each other.
@item overlay
Presents information identical to that in the @code{parade}, except
that the graphs representing color components are superimposed directly
over one another.
-
-This display mode in @code{waveform} histogram mode makes it easier to spot
-relative differences or similarities in overlapping areas of the color
-components that are supposed to be identical, such as neutral whites, grays,
-or blacks.
@end table
Default is @code{parade}.
@item levels_mode
-Set mode for @code{levels}. Can be either @code{linear}, or @code{logarithmic}.
+Set mode. Can be either @code{linear}, or @code{logarithmic}.
Default is @code{linear}.
@item components
-Set what color components to display for mode @code{levels}.
+Set what color components to display.
Default is @code{7}.
@end table
@table @option
@item inputs
Set number of input streams. Default is 2.
+
+@item shortest
+If set to 1, force the output to terminate when the shortest input
+terminates. Default value is 0.
@end table
@section hue
@table @option
@item inputs
Set number of input streams. Default is 2.
+
+@item shortest
+If set to 1, force the output to terminate when the shortest input
+terminates. Default value is 0.
@end table
@section w3fdif
probability for the current frame to introduce a new scene, while a higher
value means the current frame is more likely to be one (see the example below)
+@item concatdec_select
+The concat demuxer can select only part of a concat input file by setting an
+inpoint and an outpoint, but the output packets may not be entirely contained
+in the selected interval. By using this variable, it is possible to skip frames
+generated by the concat demuxer which are not exactly contained in the selected
+interval.
+
+This works by comparing the frame pts against the @var{lavf.concat.start_time}
+and the @var{lavf.concat.duration} packet metadata values which are also
+present in the decoded frames.
+
+The @var{concatdec_select} variable is -1 if the frame pts is at least
+start_time and either the duration metadata is missing or the frame pts is less
+than start_time + duration, 0 otherwise, and NaN if the start_time metadata is
+missing.
+
+That basically means that an input frame is selected if its pts is within the
+interval set by the concat demuxer.
+
@end table
The default value of the select expression is "1".
@example
select=n=2:e='mod(n, 2)+1' [odd][even]; [odd] pad=h=2*ih [tmp]; [tmp][even] overlay=y=h
@end example
+
+@item
+Select useful frames from an ffconcat file which is using inpoints and
+outpoints but where the source files are not intra frame only.
+@example
+ffmpeg -copyts -vsync 0 -segment_time_metadata 1 -i input.ffconcat -vf select=concatdec_select -af aselect=concatdec_select output.avi
+@end example
@end itemize
@section selectivecolor
Set border width, allowed range is [0, 5]. Default is 1.
@item w
-Set channel width, allowed range is [40, 1080]. Default is 400.
+Set channel width, allowed range is [80, 1080]. Default is 400.
@item h
Set channel height, allowed range is [1, 100]. Default is 20.
@item f
-Set fade, allowed range is [1, 255]. Default is 20.
+Set fade, allowed range is [0.001, 1]. Default is 0.95.
@item c
Set volume color expression.
@item t
If set, displays channel names. Default is enabled.
+
+@item v
+If set, displays volume values. Default is enabled.
@end table
@section showwaves
projects / ffmpeg / blobdiff