# get a single value out of ffprobe
# $ probe a:0 sample_rate in.flac
probe() {
    [ "$1" = "fmt" ] &&
        ffprobe -v error -show_entries format=$2 -of default=nk=1:nw=1 "$3" ||
        ffprobe -v error -select_streams $1 -show_entries stream=$2 -of default=nk=1:nw=1 "$3"
}