feat: add audio mode option to videncode script

.local/bin/videncode

@@ -44,6 +44,7 @@ OVERWRITE_DIFFERENT=false
 IS_BATCH=false
 INPUT_DIR=""
 INPUT_FILES=()
+AUDIO_MODE="transcode"
 
 # Prints usage information to stdout.
 usage() {
@@ -62,6 +63,7 @@ Usage: $(basename "$0") -i input.mp4 [options]
     --max-h                Maximum height in pixels (default: ${DEFAULT_MAX_H})
     --overwrite-same       Overwrite output even if duration matches input
     --overwrite-different  Overwrite output even if duration differs from input
+    --audio-mode           Audio mode: transcode (default) or copy
     -h, --help             Show this help
 EOF
 }
@@ -86,6 +88,7 @@ parse_args() {
       --max-h) MAX_H="$2"; shift 2 ;;
       --overwrite-same) OVERWRITE_SAME=true; shift ;;
       --overwrite-different) OVERWRITE_DIFFERENT=true; shift ;;
+       --audio-mode) AUDIO_MODE="$2"; shift 2 ;;
       -h|--help) usage; exit 0 ;;
       --) shift; break ;;
       *) echo "Unknown argument: $1" >&2; usage; exit 1 ;;
@@ -148,8 +151,13 @@ validate_input_single() {
 
 # Assembles the full ffmpeg command array with all configured options.
 build_ffmpeg_cmd() {
-  # Sets audio flags to copy streams unchanged for fidelity.
-  local audio_flags=("-c:a" "copy")
+   # Sets audio flags to transcode to Opus or copy streams unchanged.
+   local audio_flags
+   if [[ "$AUDIO_MODE" == "transcode" ]]; then
+     audio_flags=("-c:a" "libopus")
+   else
+     audio_flags=("-c:a" "copy")
+   fi
 
   # Constructs the ffmpeg video scaling filter to fit within max dimensions while preserving aspect ratio.
   # Scale logic: for landscape (w>h), constrain width to MAX_W and height to MAX_H;