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FilteringGuide

FFmpeg Filtering Guide

FFmpeg has access to many filters and more are added on a regular basis. To see what filters are available with your build see ffmpeg -filters.

Documentation

Refer to the FFmpeg filters documentation for more information and examples for each filter. This wiki page is for user contributed examples and tips, and contributions to this page are encouraged.

Filter syntax

When documentation refers to "filter options", or says the "filter accepts the following options", the syntax to use for the options is as described in FFmpeg Filters, section 4.1 Filtergraph syntax. Briefly, that syntax is to add, after the name of the filter, an = character, then the name of the first filter option, an = character, and the value of that option. If you want to specify further filter options, you delimit them with :, then append the name of the next filter option, an = character, and the next value.

For instance, to apply the loudnorm filter to an audio stream, the basic syntax is:

ffmpeg -i input -filter:a loudnorm  output

To add the print_format and linear filter options, use the syntax:

ffmpeg -i input -filter:a loudnorm=print_format=summary:linear=true  output

As described in section 4.1 Filtergraph syntax, you can omit the option names and = characters, supplying just the values, delimited by : characters. For example, in this invocation:

ffmpeg -i input -vf scale=iw/2:-1 output

FFmpeg assumes the option names in the order they are declared in the source code. For instance, in this use of the scale filter, FFmpeg assumes the option name width for the value iw/2, and the name height for the value -1.

Filtergraph, Chain, Filter relationship

What follows the -vf in an ffmpeg command line is a filtergraph description. This filtergraph may contain a number of chains, each of which may contain a number of filters.

Whilst a full filtergraph description can be complicated, it is possible to simplify it for simpler graphs provided ambiguity is avoided.

Remembering that filters in a chain are separated by commas "," chains by a semicolon ";" and that if an input or output is not specified it is assumed to come from the preceding or sent to the following item in the chain.

The following are equivalent:

ffmpeg -i input -vf [in]scale=iw/2:-1[out] output
ffmpeg -i input -vf scale=iw/2:-1 output                                      # the input and output are implied without ambiguity

As are:

ffmpeg -i input -vf [in]yadif=0:0:0[middle];[middle]scale=iw/2:-1[out] output # 2 chains form, one filter per chain, chains linked by the [middle] pad
ffmpeg -i input -vf [in]yadif=0:0:0,scale=iw/2:-1[out] output                 # 1 chain form, with 2 filters in the chain, linking implied
ffmpeg -i input -vf yadif=0:0:0,scale=iw/2:-1  output                         # the input and output are implied without ambiguity

Escaping characters

As described in the documentation, it can be necessary to escape commas "," that need to appear in some arguments, for example the select filter:

ffmpeg -i input -vf select='eq(pict_type\,I)' -vsync vfr output_%04d.png        # to select only I frames

However an alternative, which also allows for white space within the filtergraph, and which may assist in clarity of reading complex graphs, is to enclose the whole filtergraph within double quotes " " thus:

ffmpeg -i input -vf "select='eq(pict_type,I)'" output       # to select only I frames
ffmpeg -i input -vf "yadif=0:-1:0, scale=iw/2:-1" output    # deinterlace then resize

Note that the examples given in the documentation mix and match the use of "full quoting" and "\" escaping, and that use of unusual shells may upset escaping. See Notes on filtergraph escaping for more information.

Examples

Scaling

Starting with something simple. Resize a 640x480 input to a 320x240 output.

ffmpeg -i input -vf scale=iw/2:-1 output

iw is input width. In this example the input width is 640. 640/2 = 320. The -1 tells the scale filter to preserve the aspect ratio of the output, so in this example the scale filter will choose a value of 240. See the FFmpeg documentation for additional information.

Speed up your video

See How to speed up / slow down a video for examples.

Multiple input overlay in 2x2 grid

Here four inputs are filtered together using the -filter_complex option. In this case all of the inputs are the -f lavfi -i testsrc (the testsrc source filter) but could be other inputs.

Within the filtergraph the first input is unchanged, and the other three inputs are individually filtered using hflip, negate, and edgedetect. The hstack and vstack filters are then used to stack each video into the desired location.

ffmpeg -f lavfi -i testsrc -f lavfi -i testsrc -f lavfi -i testsrc -f lavfi -i testsrc -filter_complex \
"[1:v]negate[a]; \
 [2:v]hflip[b]; \
 [3:v]edgedetect[c]; \
 [0:v][a]hstack=inputs=2[top]; \
 [b][c]hstack=inputs=2[bottom]; \
 [top][bottom]vstack=inputs=2[out]" -map "[out]" -c:v ffv1 -t 5 multiple_input_grid.avi

This next example is the same as above, but uses the pad and overlay filters instead. The pad filter is used to make an appropriate sized background, and overlay is used to place each video into the correct location. This method is slower than using hstack + vstack as shown above.

ffmpeg -f lavfi -i testsrc -f lavfi -i testsrc -f lavfi -i testsrc -f lavfi -i testsrc -filter_complex \
"[0:v]pad=iw*2:ih*2[a]; \
 [1:v]negate[b]; \
 [2:v]hflip[c]; \
 [3:v]edgedetect[d]; \
 [a][b]overlay=w[x]; \
 [x][c]overlay=0:h[y]; \
 [y][d]overlay=w:h[out]" -map "[out]" -c:v ffv1 -t 5 multiple_input_grid.avi

Be aware that frames are taken from each input video in timestamp order, so it is a good idea to pass all overlay inputs through a setpts=PTS-STARTPTS filter to have them begin in the same zero timestamp, such as [0:v]hflip,setpts=PTS-STARTPTS[a];[1:v]setpts=PTS-STARTPTS[b];[a][b]overlay.

Burnt in Timecode

Using the drawtext video filter.

PAL 25 fps non drop frame:

ffmpeg -i in.mp4 -vf "drawtext=fontfile=/usr/share/fonts/truetype/DroidSans.ttf: timecode='09\:57\:00\:00': r=25: \
x=(w-tw)/2: y=h-(2*lh): fontcolor=white: box=1: boxcolor=0x00000000@1" -an -y out.mp4

NTSC 30 fps drop frame

(change the : to a ; before the frame count)_________________________________________________________
                                                                                                     \
ffmpeg -i in.mp4 -vf "drawtext=fontfile=/usr/share/fonts/truetype/DroidSans.ttf: timecode='09\:57\:00\;00': r=30: \
x=(w-tw)/2: y=h-(2*lh): fontcolor=white: box=1: boxcolor=0x00000000@1" -an -y out.mp4

Synthetic Input

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

This example will create a 10 second output, 30 fps (300 frames total), with a frame size of 1280x720:

ffmpeg -f lavfi -i testsrc=duration=10:size=1280x720:rate=30 output.mpg

ffplay can also be used to view the resulting filtergraph:

ffplay -f lavfi -i "testsrc=duration=10:size=1280x720:rate=30"

You can also specify testsrc as a filter:

ffmpeg -filter_complex testsrc OUTPUT

Another type of testsrc is using the smptebars source filter:

ffmpeg -f lavfi -i "smptebars=duration=5:size=1280x720:rate=30" output.mp4

Or a color

./ffmpeg -f lavfi -i color=c=red:size=100x100

There are other options for generating synthetic video input, see here and here ("generic equation" filter).

Other Filter Examples

Filter Metadata

Filters may write metadata entries that can be used for debugging their functionality, or extracting additional information from the input file. For a general description, see the metadata filter documentation.

Metadata keys are defined by the respective filters, and there is no globally accessible list. Some of them are mentioned in the filter documentation itself.

Here are some important metadata keys, all starting with lavfi.<filter>, where <filter> is the name of the filter itself.

Filter Key Description
aphasemeter phase
astats Bit_depth2
astats Bit_depth
astats Crest_factor
astats DC_offset
astats Dynamic_range
astats Flat_factor
astats Max_difference
astats Max_level
astats Mean_difference
astats Min_difference
astats Min_level
astats Overall.Bit_depth2
astats Overall.Bit_depth
astats Overall.DC_offset
astats Overall.Flat_factor
astats Overall.Max_difference
astats Overall.Max_level
astats Overall.Mean_difference
astats Overall.Min_difference
astats Overall.Min_level
astats Overall.Number_of_samples
astats Overall.Peak_count
astats Overall.Peak_level
astats Overall.RMS_difference
astats Overall.RMS_level
astats Overall.RMS_peak
astats Overall.RMS_trough
astats Peak_count
astats Peak_level
astats RMS_difference
astats RMS_level
astats RMS_peak
astats RMS_trough
astats Zero_crossings_rate
astats Zero_crossings
bbox h
bbox w
bbox x1
bbox x2
bbox y1
bbox y2
blackframe pblack
cropdetect h
cropdetect w
cropdetect x1
cropdetect x2
cropdetect x
cropdetect y1
cropdetect y2
cropdetect y
ebur128 r128.I
ebur128 r128.LRA.high
ebur128 r128.LRA.low
ebur128 r128.LRA
ebur128 r128.M
ebur128 r128.S
freezedetect freeze_duration Duration of the freeze period
freezedetect freeze_end End of the freeze period
freezedetect freeze_start Start of the freeze period
psnr mse.u
psnr mse.v
psnr mse.y
psnr mse_avg
psnr psnr.u
psnr psnr.v
psnr psnr.y
psnr psnr_avg
signalstats HUEAVG
signalstats HUEMED
signalstats key
signalstats SATAVG
signalstats SATHIGH
signalstats SATLOW
signalstats SATMAX
signalstats SATMIN
signalstats UAVG
signalstats UBITDEPTH
signalstats UDIF
signalstats UHIGH
signalstats ULOW
signalstats UMAX
signalstats UMIN
signalstats VAVG
signalstats VBITDEPTH
signalstats VDIF
signalstats VHIGH
signalstats VLOW
signalstats VMAX
signalstats VMIN
signalstats YAVG
signalstats YBITDEPTH
signalstats YDIF
signalstats YHIGH
signalstats YLOW
signalstats YMAX
signalstats YMIN
silencedetect silence_duration Duration of the silence period
silencedetect silence_end End of the silence period
silencedetect silence_start Start of the silence period
ssim All
ssim dB
ssim u
ssim v
ssim y

Scripting Filters

From a File

Suppose you want to change some filter parameters based on an input file. Some filters support the option to receive commands via `sendcmd`. Run ffmpeg -filters and check the C column – if it is present, a filter supports receiving input this way.

For example, if you want to rotate the input at seconds 0, 1, and 2, create a file called cmd.txt with the content:

0 rotate angle '45*PI/180';
1 rotate angle '90*PI/180';
2 rotate angle '180*PI/180';

Now run an example stream:

ffmpeg -f lavfi -i testsrc -filter_complex "[0:v]sendcmd=f=cmd.txt,rotate" -f matroska - | ffplay -

Some examples of this technique can be seen here.

With a Shell Script

When building complex filtergraphs, it may help to break the command down into manageable pieces. However one needs to be careful when joining them all together, in order to avoid issues due escaped characters.

The following example shows a sample bash script containing a filtergraph of one chain with three filters: yadif, scale and drawtext.

#!/bin/bash
# ffmpeg test script

path="/path/to/file/"

in_file="in.mp4"
out_file="out.mp4"

cd $path

filter="yadif=0:-1:0, scale=400:226, drawtext=fontfile=/usr/share/fonts/truetype/DroidSans.ttf: \
text='tod- %X':x=(w-text_w)/2:y=H-60 :fontcolor=white :box=1:boxcolor=0x00000000@1"
codec="-vcodec libx264  -pix_fmt yuv420p -b:v 700k -r 25 -maxrate 700k -bufsize 5097k"

command_line=(ffmpeg -i "$in_file" -vf "$filter" "$codec" -an $out_file")

echo "${command_line[@]}"
"${command_line[@]}"
exit

Note that the filtergraph spans more than one line. The echo command shows the full command as it is executed. This is useful for debugging.

The array in the $command_line variable helps avoid loss of the quotes which occurs otherwise. Other shells may behave differently.

Developing your own Filters

Last modified 4 months ago Last modified on Nov 29, 2019, 12:15:28 PM

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