convert_screencapture.sh

convert_screencapture.sh

#!/bin/bash
# Convert macOS screencapture recording to variable frame rate to better compress low motion sequences (reduces size by ~90%).
set -e -u -o pipefail

: "${INPUT:=${1:-}}"
: "${OUTPUT:=${2:-"${INPUT%.*}-$(date +%Y%m%dT%H%M%S).${INPUT##*.}"}}"

: "${Q:=55}"    # video quality (0-100)
: "${G:=300}"   # max I-frame gap in frames
: "${BF:=1}"    # use B-frames -- videotoolbox defaults to 0 which wastes a lot on mostly static content
: "${ABR:=96k}" # audio bitrate

[ -f "$INPUT" ] || { echo "Expected input file."; exit 1; }

ffmpeg \
  -hwaccel videotoolbox \
  -i "$INPUT" \
  -map 0:v:0 \
  -map '0:a?' -c:a aac_at -b:a "$ABR" \
  -map_metadata 0 \
  -c:v hevc_videotoolbox -q:v "$Q" -g "$G" -bf "$BF" \
  -fps_mode:v vfr -enc_time_base:v demux \
  -prio_speed 0 -spatial_aq 1 \
  -tag:v hvc1 \
  -movflags +faststart+use_metadata_tags \
  "$OUTPUT"