avirename.sh

#!/bin/sh
for file in "$@"; do
  [ ! -f "$file" ] && continue
  t="$(file "$file" --mime-type -b)"
  if [ "$t" = "video/x-ms-asf" ]; then
    mv -i "$file" "${file%.*}.wmv"
  fi
  if [ "$t" = "video/mp4" ]; then
    mv -i "$file" "${file%.*}.mp4"
  fi
done