refactor(preset): return ffargs via nameref instead of global variable

load_preset now accepts the name of the caller's array as a second
argument and populates it via a nameref (local -n), replacing the
previous implicit global ffargs. The preset is sourced into a local
ffargs contained within load_preset's scope and copied to the caller
on return.

encode_one declares its own local ffargs=() and passes its name to
load_preset, making the data flow explicit and eliminating the implicit
coupling through the global. The nameref variable is prefixed with an
underscore to avoid accidental aliasing of any same-named local in the
calling scope.

1 files changed, 15 insertions, 3 deletions

diff --git a/transcode.sh b/transcode.sh
index f3b5a4a..6b0bb22 100755
--- a/transcode.sh
+++ b/transcode.sh
@@ -339,6 +339,10 @@ fi
 
 # Load ffmpeg argument preset by name.
 #
+# Arguments:
+#   $1 - preset name
+#   $2 - name of the caller's array variable to populate (nameref)
+#
 # Security:
 #   Presets are sourced as shell code. Names are validated against a strict
 #   allowlist (alphanumerics, hyphens, underscores only) to prevent path
@@ -350,8 +354,12 @@ fi
 #   The sourced preset MUST set the bash array `ffargs`.
 #   Presets may reference variables from the caller (encode_one) such as:
 #     output_pixel_format, input_pixel_format, input_codec
+#   On return the caller's array (named by $2) is populated with the preset's
+#   ffargs; the preset-local `ffargs` variable is unset before returning.
 load_preset() {
   local preset="$1"
+  local -n _load_preset_out="$2"
+
   # Strict allowlist: only alphanumerics, hyphens, and underscores are permitted.
   # This prevents path traversal, shell metacharacter injection, and symlink-based
   # attacks more reliably than a blocklist approach.
@@ -381,8 +389,7 @@ load_preset() {
     exit $EXIT_CONFIG_ERROR
   fi
 
-  unset -v ffargs
-  ffargs=()
+  local ffargs=()
 
   debug "Sourcing preset file:" "$file"
 
@@ -395,6 +402,8 @@ load_preset() {
   }
 
   debug "Preset ffargs:" "$(printf "%q " "${ffargs[@]}")"
+
+  _load_preset_out=("${ffargs[@]}")
 }
 
 if [[ $# -eq 0 ]]; then
@@ -685,7 +694,10 @@ encode_one() {
   fi
   debug "Selected output pixel format:" "$output_pixel_format"
 
-  load_preset "$PRESET_NAME"
+  # Load preset early so a missing/invalid preset fails before we create a
+  # temp file or do any further work.
+  local ffargs=()
+  load_preset "$PRESET_NAME" ffargs
 
   local extension filename directory tmp base stem