Generate Constant Tone with FFmpeg Sine Filter

Generating audio tones programmatically is a fast and efficient task using FFmpeg's built-in sine audio filter. This article provides a straightforward guide on how to configure the sine filter to generate a constant tone, adjust its frequency, define its duration, and specify a custom audio sample rate.

The Basic Command

To generate a tone using the sine filter, use the lavfi (Libavfilter) input format with the -f flag. The parameters for frequency, sample rate, and duration are passed directly to the filter.

ffmpeg -f lavfi -i "sine=frequency=1000:sample_rate=48000:duration=5" output.wav

Parameter Breakdown

• -f lavfi: Specifies Libavfilter as the virtual input device.
• -i "sine=...": Calls the sine source filter and passes its options:
  • frequency (or f): Sets the tone's pitch in Hertz (Hz). The default value is 440 Hz (standard A4 pitch).
  • sample_rate (or r): Sets the audio sampling frequency in Hz. The default is 44100 Hz. In the example above, it is explicitly set to 48000 Hz.
  • duration (or d): Specifies the duration of the audio in seconds. If omitted, the tone will generate indefinitely until stopped manually.
• output.wav: The destination audio file. You can output to formats such as .wav, .mp3, or .flac.

Alternative Method: Using the -ar Flag

You can also control the sample rate using FFmpeg’s standard audio rate option (-ar) rather than defining it inside the filter string.

ffmpeg -f lavfi -i "sine=f=440:d=10" -ar 96000 output.wav

In this command, the sine filter generates the tone at its default internal rate, and FFmpeg resamples the final stream to 96,000 Hz before encoding the output file. However, setting sample_rate directly inside the filter is generally preferred to avoid unnecessary resampling steps.