How to Generate a Siren Audio Tone in FFmpeg
This article provides a quick guide on how to synthesize a custom
siren audio tone using FFmpeg. Although FFmpeg does not have a native
filter named “siren,” you can easily generate a realistic,
frequency-modulated siren sound using the aevalsrc (audio
evaluation source) filter or create constant tones using the
sine filter. Below, you will find the exact command-line
instructions needed to synthesize these audio tones and save them
directly to your system.
Generating a Siren Tone
with aevalsrc
The most effective way to create a classic wailing siren sound in
FFmpeg is to use the aevalsrc filter. This filter allows
you to use mathematical expressions to modulate a sine wave’s frequency
over time.
Run the following command to generate a 10-second modulated siren tone:
ffmpeg -f lavfi -i "aevalsrc=sin(2*PI*t*(600+200*sin(2*PI*t*0.5)))" -t 10 siren.wavHow it works: * -f lavfi: Specifies
that FFmpeg should use the Libreavfilter input virtual device. *
aevalsrc: Synthesizes an audio signal based on the
expression provided. * 600: The base frequency of the tone
in Hertz (Hz). * 200*sin(...): Modulates the frequency up
and down by 200 Hz. * 0.5: Controls the speed of the
siren’s oscillation (wail rate). * -t 10: Sets the output
duration to 10 seconds.
Generating a
Standard Constant Tone with sine
If you meant to use the basic sine generator filter to
create a flat, continuous synthesized tone instead of a modulated siren,
you can use the following command:
ffmpeg -f lavfi -i "sine=frequency=1000:duration=5" constant_tone.wavHow it works: * sine=frequency=1000:
Generates a pure sine wave tone at 1000 Hz. * duration=5:
Sets the generated audio length to 5 seconds.
Generating a Fast-Paced “Yelp” Siren
To create a faster, emergency-vehicle style “yelp” siren, increase
the modulation speed in the aevalsrc filter:
ffmpeg -f lavfi -i "aevalsrc=sin(2*PI*t*(800+300*sin(2*PI*t*3)))" -t 10 fast_siren.wavBy adjusting the numbers inside the mathematical expression, you can synthesize a wide variety of custom alert tones, sweeps, and sirens directly within FFmpeg.