#!/bin/bash

function wavtovid {
    DURATION=$(($(mediainfo --output=General\;%Duration% "$0") / 1000))
    OUTNAME=$(basename "$0" .wav).mkv
    ffmpeg -i "$0" -loop 1 -f image2 -i bgsimple.bmp -acodec copy -r 30 -t ${DURATION} "${OUTNAME}"
}
export -f wavtovid

find . -name "*.wav" -type f -print0 | xargs -0 -n 1 -P 1 -i bash -c 'wavtovid "$@"' {}