FFmpeg Filtering Guide 多视频叠加

FFmpeg Filtering Guide

Contents

1. Documentation
2. Examples
   1. Scaling
   2. Speed up your video
   3. Filtergraph,Chain,Filter relationship
   4. multiple input overlay in 2x2 grid
   5. Escaping characters
   6. Burnt in Timecode
   7. Scripting your command line parameters
   8. Synthetic Input
   9. Other Filter Examples
   10. Developing your own Filters

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

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.

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

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 padded to the right and bottom by double its height, and the other three inputs are individually filtered using hflip, negate, and edgedetect.

The overlay video filter is then used multiple times for placement of each input. The offsets used in the overlay filter arrange the inputs into a grid shape.

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.

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\,PICT_TYPE_I)' output                         # 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,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.

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

Scripting your command line parameters

If building complex filtergraphs the command line can get very messy so it can help to break things down into manageable pieces. However one needs to be careful when joining them all together to avoid issues due to your shell and 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. Useful for debugging.

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

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

• Fancy Filtering Examples – Examples for various psychedelic effects and other weird filtering.

• Null describes the nullsink filter.

Developing your own Filters