dnywh · February 4, 2026 23:58
diff --git a/shrinkvid.zsh b/shrinkvid.zsh
 # shrinkvid - batch shrink videos with ffmpeg
 # --------------------------------------------
 # Usage:
 #   shrinkvid [directory] [format] [crf] [scale_pct]
 #
 # Examples:
 #   shrinkvid                 # defaults: ~/Downloads, mp4, CRF=25
 #   shrinkvid . mp4 25 50     # 50% size
 #   shrinkvid ~/Movies        # custom directory
 #   shrinkvid . mkv 24        # current dir, mkv files, CRF=24
 #
 # Notes:
 # - Originals are renamed with `_Original` suffix.
 # - Skips files already ending in `_Original`.
 # - Does not overwrite existing `_Original` files.
 #
 # Important:
 # - libx264 commonly requires width/height divisible by 2 (e.g. yuv420p).
 #   Some inputs (or scaled results) can end up odd-sized, e.g. 1728x1117.
 #   This function forces the final dimensions to be even by rounding DOWN
 #   to the nearest multiple of 2 (changes at most 1px in each dimension).

 shrinkvid() {
  emulate -L zsh
  set -o pipefail
  setopt null_glob

  local dir="${1:-$HOME/Downloads}"
  local fmt="${2:-mp4}"
  local crf="${3:-25}" # 28 is very aggressive, 23 is almost visually the same as input
  local scale_pct="${4:-}"

  # Video filter:
  # - If scale_pct is provided, scale by that percentage.
  # - Always ensure the output width/height are even numbers by truncating down:
  #     trunc(x/2)*2  -> nearest even <= x
  #
  # This avoids: "height not divisible by 2" and similar libx264 encoder errors.
  local vf=""
  if [[ -n "$scale_pct" ]]; then
    # Scale *then* coerce to even dimensions (rounding down).
    vf="-vf scale=trunc(iw*${scale_pct}/100/2)*2:trunc(ih*${scale_pct}/100/2)*2"
  else
    # No scaling requested, but still coerce to even dimensions if needed.
    # If input is already even-sized, this is a no-op.
    vf="-vf scale=trunc(iw/2)*2:trunc(ih/2)*2"
  fi

  builtin pushd -q "$dir" || { echo "Directory not found: $dir"; return 1; }

  for i in *.${fmt}; do
    [[ "$i" == *_Original.${fmt} ]] && continue
    local original="${i%.*}_Original.${fmt}"
    mv -n -- "$i" "$original" || { echo "Skipping $i (backup exists)"; continue; }

    echo "Shrinking $i (CRF=$crf${scale_pct:+, scale=${scale_pct}%})..."
    echo "  Applying filter: ${vf#-vf }"
    echo "  Output dims will be forced to even numbers (rounded down if needed)."

    ffmpeg -y -i "$original" \
      -c:v libx264 -preset slow -crf "$crf" \
      ${=vf} \
      -c:a copy \
      "$i"
  done

  popd -q
 }
	# shrinkvid - batch shrink videos with ffmpeg
	# --------------------------------------------
	# Usage:
	# shrinkvid [directory] [format] [crf] [scale_pct]
	#
	# Examples:
	# shrinkvid # defaults: ~/Downloads, mp4, CRF=25
	# shrinkvid . mp4 25 50 # 50% size
	# shrinkvid ~/Movies # custom directory
	# shrinkvid . mkv 24 # current dir, mkv files, CRF=24
	#
	# Notes:
	# - Originals are renamed with `_Original` suffix.
	# - Skips files already ending in `_Original`.
	# - Does not overwrite existing `_Original` files.
	#
	# Important:
	# - libx264 commonly requires width/height divisible by 2 (e.g. yuv420p).
	# Some inputs (or scaled results) can end up odd-sized, e.g. 1728x1117.
	# This function forces the final dimensions to be even by rounding DOWN
	# to the nearest multiple of 2 (changes at most 1px in each dimension).

	shrinkvid() {
	emulate -L zsh
	set -o pipefail
	setopt null_glob

	local dir="${1:-$HOME/Downloads}"
	local fmt="${2:-mp4}"
	local crf="${3:-25}" # 28 is very aggressive, 23 is almost visually the same as input
	local scale_pct="${4:-}"

	# Video filter:
	# - If scale_pct is provided, scale by that percentage.
	# - Always ensure the output width/height are even numbers by truncating down:
	# trunc(x/2)*2 -> nearest even <= x
	#
	# This avoids: "height not divisible by 2" and similar libx264 encoder errors.
	local vf=""
	if [[ -n "$scale_pct" ]]; then
	# Scale then coerce to even dimensions (rounding down).
	vf="-vf scale=trunc(iw${scale_pct}/100/2)2:trunc(ih${scale_pct}/100/2)2"
	else
	# No scaling requested, but still coerce to even dimensions if needed.
	# If input is already even-sized, this is a no-op.
	vf="-vf scale=trunc(iw/2)2:trunc(ih/2)2"
	fi

	builtin pushd -q "$dir" \|\| { echo "Directory not found: $dir"; return 1; }

	for i in *.${fmt}; do
	[[ "$i" == *_Original.${fmt} ]] && continue
	local original="${i%.*}_Original.${fmt}"
	mv -n -- "$i" "$original" \|\| { echo "Skipping $i (backup exists)"; continue; }

	echo "Shrinking $i (CRF=$crf${scale_pct:+, scale=${scale_pct}%})..."
	echo " Applying filter: ${vf#-vf }"
	echo " Output dims will be forced to even numbers (rounded down if needed)."

	ffmpeg -y -i "$original" \
	-c:v libx264 -preset slow -crf "$crf" \
	${=vf} \
	-c:a copy \
	"$i"
	done

	popd -q
	}
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