diff --git a/.gitignore b/.gitignore
index 9178f67..58c9f11 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,6 @@
-out/
-src/
+**
+!.gitignore
+!to-m4b.sh
 
 *~
 
diff --git a/to-m4b.sh b/to-m4b.sh
index f92d736..894d653 100755
--- a/to-m4b.sh
+++ b/to-m4b.sh
@@ -98,9 +98,15 @@ get-book-directories() {
   # - ${SRC}/<author>/<year> - <title> {<narrator>}/
   # Prints matched directories, one per line
   local src_root="${1}"
-  local -a results=()
   local dir leaf
 
+  # Ensure globbing is enabled locally (script uses set -f globally)
+  local had_noglob=0
+  case $- in
+    *f*) had_noglob=1 ;;
+  esac
+  set +f
+
   # Iterate candidate depths using fast globbing (avoids slow full-recursive find)
   for dir in "${src_root}"/*/*/ "${src_root}"/*/*/*/; do
     [[ -d "$dir" ]] || continue
@@ -117,12 +123,18 @@ get-book-directories() {
     fi
 
     # Quick check: directory contains at least one likely audio file
-    if compgen -G "$dir"*.{mp3,m4a,m4b,aac,flac,wav} >/dev/null 2>&1; then
-      results+=("${dir%/}")
-    fi
+    local found=0 ext
+    for ext in mp3 m4a m4b aac flac wav ogg; do
+      if compgen -G "$dir"*."$ext" >/dev/null 2>&1; then
+        found=1
+        break
+      fi
+    done
+    (( found )) && printf '%s\n' "${dir%/}"
   done
 
-  printf '%s\n' "${results[@]}"
+  # Restore previous noglob state
+  (( had_noglob )) && set -f || true
 }
 
 m4b-merge() {
@@ -135,21 +147,38 @@ m4b-merge() {
   local series="${7}"
   local series_index=${8}
 
+  # Ensure destination directory exists
   mkdir -p "$(dirname "${output_file}")"
-  nix run github:sandreas/m4b-tool#m4b-tool-libfdk -- \
-    merge \
-      -v \
-      --jobs=6 \
-      --audio-samplerate=44100 \
-      --audio-quality=100 \
-      --writer="${author}" \
-      --artist="${narrator}" \
-      --title="${title}" \
-      --year="${year}" \
-      --album="${series}" \
-      --album-sort="${series_index}" \
-      --output-file="${output_file}/" \
-      -- "${source_dir}"
+
+  # Build args; add series flags only when present (standalone-friendly)
+  local args=(
+    merge
+    -v
+    --jobs=6
+    --audio-samplerate=44100
+    --audio-quality=100
+  )
+  if [[ -n "${author}" ]]; then
+    args+=("--writer=${author}")
+  fi
+  if [[ -n "${narrator}" ]]; then
+    args+=("--artist=${narrator}")
+  fi
+  if [[ -n "${title}" ]]; then
+    args+=("--album=${title}")
+  fi
+  if [[ -n "${year}" ]]; then
+    args+=("--year=${year}")
+  fi
+  if [[ -n "${series}" ]]; then
+    args+=("--series=${series}")
+  fi
+  if [[ -n "${series_index}" ]]; then
+    args+=("--series-part=${series_index}")
+  fi
+  args+=("--output-file=${output_file}" -- "${source_dir}")
+
+  nix run github:sandreas/m4b-tool#m4b-tool-libfdk -- "${args[@]}"
 }
 
 main() {
@@ -157,28 +186,44 @@ main() {
   local out_root="${OUT:-${script_dir}/out}"
   local dir author narrator title year series series_index output_file
 
-  mapfile -t dirs < <(get-book-directories "${src_root}")
+  # Build array of directories without using mapfile (Bash 3 compatibility)
+  # Portable array fill (Bash 3): split on newlines only
+  {
+    IFS=$'\n'
+    dirs=($(get-book-directories "${src_root}"))
+  }
 
-  for dir in "${dirs[@]}"; do
-    eval "$(parse-vars "$dir")"
-    if [[ -z "$title" ]]; then
-      echo "Skipping '$dir': could not parse title" >&2
-      continue
-    fi
+  if ((${#dirs[@]})); then
+    for dir in "${dirs[@]}"; do
+      eval "$(parse-vars "$dir")"
+      if [[ -z "$title" ]]; then
+        echo "Skipping '$dir': could not parse title" >&2
+        continue
+      fi
     if [[ -z "$author" ]]; then
       echo "Skipping '$dir': could not parse author" >&2
       continue
     fi
     # Construct output path: ${OUT}/<author>/<series or standalone>/<series_index - >title {narrator}.m4b
     if [[ -n "$series" ]]; then
-      output_file="${out_root}/${author}/${series}/${series_index:+${series_index} - }${title}${narrator:+ {${narrator}}}.m4b"
+      output_file="${out_root}/${author}/${series}/"
+      [[ -n "$series_index" ]] && output_file+="Book ${series_index} - "
+      [[ -n "$year" ]] && output_file+="${year} - "
+      output_file+="${title}"
     else
-      output_file="${out_root}/${author}/${year:+${year} - }${title}${narrator:+ {${narrator}}}.m4b"
+      output_file="${out_root}/${author}/"
+      [[ -n "$year" ]] && output_file+="${year} - "
+      output_file+="${title}"
     fi
+    [[ -n "$narrator" ]] && output_file+=" {${narrator}}"
+    output_file+=".m4b"
 
-    echo "Processing '$dir' -> '$output_file'"
-    # m4b-merge "$output_file" "$dir" "$author" "$narrator" "$title" "$year" "$series" "$series_index"
-  done
+      echo "Processing '$dir' -> '$output_file'"
+      m4b-merge "$output_file" "$dir" "$author" "$narrator" "$title" "$year" "$series" "$series_index"
+    done
+  else
+    echo "No book directories found under '${src_root}'." >&2
+  fi
 }
 
 main "$@"