relax

#!/bin/sh

help() {
	cat - >&2 <<EOF
relax - plays some relaxing noise

relax [--ffplay|--mpv|--ffmpeg|--sox]

Plays brown noise that fades in at the start, then continues with a
couple of slow, shallow, tremolo filters that are slightly offset from
each other to give the appearance of random/subtle "waves"

If a backend isn't specified then one will be automatically selected
in the same order as below:
	--ffplay (requires ffmpeg compiled with SDL)
	--mpv (requires mpv)
	--ffmpeg (requires ffmpeg, only plays into alsa)
	--sox (requires sox)
EOF
}

lavfifilter="anoisesrc=color=brown,afade=type=in:duration=90,tremolo=f=0.1:d=0.1,tremolo=f=0.16:d=0.2"

case "$1" in
	--ffplay)  backend=ffplay ;;
	--mpv)     backend=mpv ;;
	--sox)     backend=sox ;;
	--ffmpeg)  backend=ffmpeg ;;
	--help|-h) help; exit 0;;
	*)
		if command -v ffplay > /dev/null 2>&1; then
			backend=ffplay
		elif command -v mpv > /dev/null 2>&1; then
			backend=mpv
		elif command -v ffmpeg > /dev/null 2>&1; then
			backend=ffmpeg
		elif command -v play > /dev/null 2>&1; then
			backend=sox
		else
			printf '%s\n' "error: couldn't find a suitable backend. please install one of the following:" \
				'mpv' 'ffmpeg' 'sox' >&2
			exit 1
		fi
		;;
esac

case "$backend" in
	ffplay)
		exec ffplay -nodisp -f lavfi -i "$lavfifilter"
		;;
	mpv)
		exec mpv --no-config av://lavfi:"$lavfifilter"
		;;
	ffmpeg)
		exec ffmpeg -f lavfi -i "$lavfifilter" -f alsa default
		;;
	sox)
		exec play -Gn \
			synth brownnoise \
			tremolo 0.10 10 \
			tremolo 0.16 20 \
			fade t 90
		;;
esac