Ciro Santilli @cirosantilli 35

Filter graphs are a thing of great beauty. What an amazingly obscure domain-specific language, but which can produce striking results with very little!!!

A quick example from stackoverflow.com/questions/59551013/how-to-generate-stereo-sine-wave-using-ffmpeg-with-different-frequencies-for-eac/77730492#77730492 illustrates some of the fundamentals:

ffplay -autoexit -nodisp -f lavfi -i '
sine=frequency=500[a];
sine=frequency=1000[b];
[a][b]amerge, atrim=end=2
'

which creates a graph:

                              +--------+
[sine=frequency=500]--->[a]-->|        |
                              | amerge |-->[atrim]-->[output]
[sine=frequency=1000]-->[b]-->|        |
                              +--------+

and plays 500 Hz on the left channel and 1000 Hz on the right channel for 2 seconds.

So we see the following syntax patterns:

sine, amerge and atrim are filters
sine=frequency=500: the first = says "araguments follow"
- frequency=500 sets the frequency argument of the sine filter
- for multiple arguments the syntax is to separate arguments with colons e.g. sine=frequency=500:duration=2
;: separates statements
[a], [b]: sets the name of an edge
,: creates unnamed edge between filters that have one input and one output

A list of all filters can be obtained ith:

ffmpeg -filters

and parameters for a single filter can be obtained with:

ffmpeg --help filter=sine

TODO dump graph to ASCII art? trac.ffmpeg.org/wiki/FilteringGuide#Visualizingfilters mentions a -dumpgraph option, but haven't managed to use it yet.

Bibliography:

ffmpeg.org/ffmpeg-filters.html official documentation
trac.ffmpeg.org/wiki/FilteringGuide some handy tips from the FFMpeg Wiki

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ffplay by

Ciro Santilli 35  Updated 2025-04-24  +Created 1970-01-01

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Awesome tool to view quick stuff quickly without generating files. Unfortunately it doesn't support all options that the ffmpeg CLI supports, e.g. ffplay multiple input files. One day, one day.

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FFmpeg sound synthesis by

Ciro Santilli 35  Updated 2025-04-24  +Created 1970-01-01

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Simple sines and variants:

2 second 1000 Hz:

ffmpeg -f lavfi -i "sine=f=1000:d=2" out.wav

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FFmpeg video synthesis by

Ciro Santilli 35  Updated 2025-04-24  +Created 1970-01-01

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Video with a solid color:

2 second white video:

ffplay -autoexit -f lavfi -i 'color=white:640x480:d=3,format=rgb24,trim=end=2'

Also add some audio:

ffmpeg -lavfi "color=white:640x480:d=3,format=rgb24,trim=end=2[v];sine=f=1000:d=2[a]" -map '[a]' -map '[v]' out.mkv

TODO how to ffplay the video + audio directly? -map does not seem to work unfortunately.

2 second white followed by 2 second black video:

ffplay -autoexit -f lavfi -i 'color=white:640x480:d=3,format=rgb24,trim=end=2[a];color=black:640x480:d=3,format=rgb24,trim=end=2[b];[a][b]concat=n=2:v=1:a=0'

bibliography:
- superuser.com/questions/1153930/how-to-generate-a-pure-white-background-video-with-ffmpeg

Display count in seconds on the video:

black text on white background. Start from 0 and count up to 2:

ffplay -autoexit -f lavfi -i "
color=white:480x480:d=3,
format=rgb24,
drawtext=
  fontcolor=black:
  fontsize=600:
  text='%{eif\:t\:d}':
  x=(w-text_w)/2:
  y=(h-text_h)/2
"

bibliography:
- gist.github.com/derand/31b8312fd64156120cb8f45825a1f0f7
- www.reddit.com/r/ffmpeg/comments/11kxugt/make_a_video_timer_or_countdown/

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Display manager by

Ciro Santilli 35  Updated 2025-04-24  +Created 1970-01-01

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Check which you you have:

systemctl status display-manager.service

Tested on Ubuntu 23.10 I see:

● gdm.service - GNOME Display Manager
     Loaded: loaded (/lib/systemd/system/gdm.service; static)
     Active: active (running) since Sun 2023-12-24 10:34:50 GMT; 23min ago
    Process: 1827 ExecStartPre=/usr/share/gdm/generate-config (code=exited, status=0/SUCCESS)
   Main PID: 1850 (gdm3)
      Tasks: 4 (limit: 71817)
     Memory: 6.8M
        CPU: 119ms
     CGroup: /system.slice/gdm.service
             └─1850 /usr/sbin/gdm3

which means I have GNOME Display Manager.

Bibliography:

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General-purpose computing on graphics processing units by