#!/bin/sh
OVERWRITE=
printf_ds()
{
  local s
  [ "$2" = 1 ] && s= || s=s
  printf "$1" "$2" "$s"
}

fail=0
skip=0
for f in "$@"
do
  out=${f%.webm}.opus
  if [ ! "$OVERWRITE" -a -e "$out" ]
  then
    skip=$((skip + 1))
    continue
  fi
  ffmpeg -i "$f" -c:a copy "$out" || fail=$((fail + 1))
done

if [ "$skip" -gt 0 ]
then
  printf_ds 'Warning: refused to overwrite %d file%s\n' "$skip" "$s" >&2
fi

if [ "$fail" -gt 0 ]
then
  printf_ds 'Error: ffmpeg failed to convert %d file%s\n' "$fail" >&2
  exit 1
fi