Convert video to MP4 with optional quality presets

convert-video.sh

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

usage() {
  cat <<'EOF'
convert-video — convert video to MP4 with optional quality presets

Usage:
  convert-video [--quality small|tiny] [--force] <input>
  convert-video --help

Options:
  -q, --quality PRESET   Re-encode with preset (small, tiny). Omit for remux.
  -f, --force            Overwrite existing output file.
  -h, --help             Show this help.

Presets:
  (default)  Stream-copy remux. Fast, lossless. Requires H.264+AAC source.
  small      960x540, CRF 26, ~35-50% of source size.
  tiny       854x480 @ 15fps, CRF 30, mono audio, ~15-25% of source size.

Output: <input-stem>.mp4 (same directory as input).
EOF
}

die() {
  echo "convert-video: $*" >&2
  exit 1
}

quality=""
force=0
input=""

while [[ $# -gt 0 ]]; do
  case "$1" in
    -q|--quality)
      [[ $# -ge 2 ]] || die "missing value for $1"
      quality="$2"
      shift 2
      ;;
    -f|--force)
      force=1
      shift
      ;;
    -h|--help)
      usage
      exit 0
      ;;
    --)
      shift
      break
      ;;
    -*)
      die "unknown flag: $1"
      ;;
    *)
      [[ -z "$input" ]] || die "only one input file allowed (got '$input' and '$1')"
      input="$1"
      shift
      ;;
  esac
done

if [[ -z "$input" ]]; then
  usage >&2
  exit 1
fi

case "$quality" in
  ""|small|tiny) ;;
  *) die "invalid --quality: '$quality' (expected: small, tiny)" ;;
esac

command -v ffmpeg >/dev/null 2>&1 \
  || die "ffmpeg not found. Install with: brew install ffmpeg"

[[ -f "$input" ]] || die "input file not found: $input"

output="${input%.*}.mp4"

if [[ -e "$output" && "$force" -ne 1 ]]; then
  die "output exists: $output
  (input: $input)
  Use --force to overwrite."
fi

success=0
trap '[[ $success -eq 1 ]] || rm -f "$output"' EXIT

ffmpeg_common=(-hide_banner -loglevel warning -stats -y -i "$input")
faststart=(-movflags +faststart)

case "$quality" in
  "")
    ffmpeg "${ffmpeg_common[@]}" -map 0 -c copy "${faststart[@]}" "$output"
    ;;
  small)
    ffmpeg "${ffmpeg_common[@]}" \
      -c:v libx264 -preset veryfast -crf 26 -vf scale=960:540 -pix_fmt yuv420p \
      -c:a aac -b:a 128k \
      "${faststart[@]}" "$output"
    ;;
  tiny)
    ffmpeg "${ffmpeg_common[@]}" \
      -c:v libx264 -preset veryfast -crf 30 -vf scale=854:480 -r 15 -pix_fmt yuv420p \
      -c:a aac -b:a 96k -ac 1 \
      "${faststart[@]}" "$output"
    ;;
esac

success=1
echo "done: $output"