A simple graphical region selector feeding into ffmpeg video recording

region_record.sh

!/usr/bin/env bash
set -euo pipefail

FPS=30
CQ=23
PRESET="p5"
AUDIO=0
USE_LAST=0
CLEAR_LAST=0

STATE_DIR="${XDG_STATE_HOME:-$HOME/.local/state}/record-region"
STATE_FILE="$STATE_DIR/last_region.env"

usage() {
  cat <<EOF
Usage:
  record-region [options]

Options:
  --last         Use the last saved region (skip selection UI)
  --clear        Clear the saved region
  --audio        Record microphone audio (PulseAudio default input)
  --fps N        Set framerate (default: ${FPS})
  --cq N         NVENC constant quality (default: ${CQ})
  -h, --help     Show this help

Notes:
  - Stop recording with Ctrl+C.
  - Output files go to ~/Videos/
EOF
}

while [[ $# -gt 0 ]]; do
  case "$1" in
    --last) USE_LAST=1; shift ;;
    --clear) CLEAR_LAST=1; shift ;;
    --audio) AUDIO=1; shift ;;
    --fps) FPS="${2:?missing value}"; shift 2 ;;
    --cq) CQ="${2:?missing value}"; shift 2 ;;
    -h|--help) usage; exit 0 ;;
    *) echo "Unknown option: $1"; usage; exit 1 ;;
  esac
done

mkdir -p "$STATE_DIR"

if [[ "$CLEAR_LAST" -eq 1 ]]; then
  rm -f "$STATE_FILE"
  echo "Cleared saved region."
  exit 0
fi

select_region() {
  # This prints shell assignments like: X=.. Y=.. W=.. H=..
  eval "$(slop -f "X=%x Y=%y W=%w H=%h")"
}

load_last_region() {
  if [[ ! -f "$STATE_FILE" ]]; then
    echo "No saved region found. Run without --last to select one first."
    exit 1
  fi
  # shellcheck disable=SC1090
  source "$STATE_FILE"
}

save_region() {
  cat > "$STATE_FILE" <<EOF
X=${X}
Y=${Y}
W=${W}
H=${H}
EOF
}

# Get region
if [[ "$USE_LAST" -eq 1 ]]; then
  load_last_region
else
  echo "Drag to select recording region..."
  select_region
  save_region
fi

# Basic validation
if [[ -z "${W:-}" || -z "${H:-}" || "$W" -le 0 || "$H" -le 0 ]]; then
  echo "Invalid region selected."
  exit 1
fi

OUT="$HOME/Videos/Screencasts/region_$(date +%F_%H-%M-%S).mp4"

echo "Recording region: ${W}x${H} at +${X},${Y}"
echo "Saving to: $OUT"
echo "Press Ctrl+C to stop."

# Build ffmpeg command
# crop filter ensures even dimensions for h264 encoding
VIDEO_INPUT=(-f x11grab -framerate "$FPS" -video_size "${W}x${H}" -i "${DISPLAY}+${X},${Y}")
VIDEO_ENC=(-vf "crop=floor(iw/2)*2:floor(ih/2)*2" -c:v h264_nvenc -preset "$PRESET" -cq "$CQ")

if [[ "$AUDIO" -eq 1 ]]; then
  ffmpeg \
    "${VIDEO_INPUT[@]}" \
    -f pulse -i default \
    "${VIDEO_ENC[@]}" \
    -c:a aac -b:a 160k \
    "$OUT"
else
  ffmpeg \
    "${VIDEO_INPUT[@]}" \
    "${VIDEO_ENC[@]}" \
    "$OUT"
fi