ffdialtone

#!/usr/bin/env bash

# ffdialtone: Generate a US (North American) dialtone with the given duration.

set -eo pipefail

function help {
    echo "Usage: ffdialtone <duration> <output>"
    exit
}

function installed {
    cmd=$(command -v "${1}")

    [[ -n "${cmd}" ]] && [[ -f "${cmd}" ]]
    return ${?}
}

function cleanup {
    rm -f "${input350}"
    rm -f "${input440}"
}

trap cleanup EXIT

[[ $# -eq 2 && ! -f $2 ]] || help
installed ffmpeg || { >&2 echo "Missing ffmpeg."; exit 1; }

input350=$(mktemp -u ffdialtone-input350-XXXXX.wav)
input440=$(mktemp -u ffdialtone-input440-XXXXX.wav)

ffmpeg -f lavfi -i "sine=frequency=350:duration=${1}" -af "volume=-13dB" "${input350}"
ffmpeg -f lavfi -i "sine=frequency=440:duration=${1}" -af "volume=-13dB" "${input440}"

# if you'd like to output in GSM full-rate:
# ffmpeg -i "${input350}" -i "${input440}" -filter_complex "amix=inputs=2:duration=first" \
#     -ar 8000 -ab 13000 -ac 1 "${2}"

ffmpeg -i "${input350}" -i "${input440}" -filter_complex "amix=inputs=2:duration=first" "${2}"