overlay.sh

#!/bin/bash

# Variables
INPUT_VIDEO="./input.mov"
OVERLAY_VIDEO="./overlay.mov"
OUTPUT_VIDEO_FILENAME="output.mov"
OVERLAY_START="0"

# Delete existing output file if it exists
if [ -f $OUTPUT_VIDEO_FILENAME ]; then
  rm $OUTPUT_VIDEO_FILENAME
fi

# Command
ffmpeg -i $INPUT_VIDEO -i $OVERLAY_VIDEO \
-filter_complex "[1:v]setpts=PTS+$OVERLAY_START/TB[a]; \
                 [0:v][a]overlay=w:h" \
-c:v libx264 -crf 18 -pix_fmt yuv420p \
$OUTPUT_VIDEO_FILENAME

# Open new video
open $OUTPUT_VIDEO_FILENAME