$ ffmpeg -y -loop 1 -r 1 -i "$IMAGE" -i test.flac -shortest -c:v libx264 -preset ultrafast -tune stillimage -pix_fmt yuv420p -c:a libfdk_aac -vbr 5 "/tmp/1_$$.mp4"

$ ffmpeg -y -loop 1 -r 1 -i "$IMAGE" -i test.m4a -shortest -c:v libx264 -preset ultrafast -tune stillimage -pix_fmt yuv420p -c:a copy "/tmp/1_$$.mp4"