crop-aigis-chrome.sh

#!/bin/bash

set -e

if [ -z "$1" ]; then
    echo "Usage: $0 <path to video which play on chrome>"
    exit 1
fi

FILEPATH="$1"
BASENAME=$(basename "$FILEPATH")
NO_EXT_BASENAME="${BASENAME%.*}"

# take a screenshot
# ref: https://trac.ffmpeg.org/wiki/Seeking

SCREENSHOT_PATH=$(mktemp -u -t XXXXXX --suffix .jpg)
ffmpeg -ss 00:00:05 -i "$FILEPATH" -frames:v 1 -q:v 5 "${SCREENSHOT_PATH}"

# get gameplay area
# ref: https://imagemagick.org/script/connected-components.php

# the output will be like:
#   20342: 960x640+470+165 963.3,484.1 589712 gray(0)
# which means:
#   id:    bounding-box    centroid    area   mean-color

TMP_STDERR=$(mktemp -u -t XXXXXX --suffix .stderr)
THRESHOLD=600000
THRESHOLD_STEP=10000

function get-segmentation-objects() {
  convert "${SCREENSHOT_PATH}" \
    -type bilevel \
    -define connected-components:area-threshold="$1" \
    -define connected-components:verbose=true \
    -connected-components 8 \
    /dev/null 2>"${TMP_STDERR}"
}

function get-gameplay-area() {
  get-segmentation-objects "$1" | jq --raw-input 'match("960x640\\S+")'
}

echo "threshold: $THRESHOLD"
CONNECTED_COMPONENT_RESULT=$(get-gameplay-area "${THRESHOLD}")
while [ -z "$CONNECTED_COMPONENT_RESULT" ] && [ -z "$(cat "$TMP_STDERR")" ] && [ "${THRESHOLD}" -gt 0 ]; do
  THRESHOLD=$((THRESHOLD - THRESHOLD_STEP))

  echo "threshold: $THRESHOLD"
  CONNECTED_COMPONENT_RESULT=$(get-gameplay-area "${THRESHOLD}")
done

if [ -z "$CONNECTED_COMPONENT_RESULT" ]; then
  echo "Failed to get gameplay area"
  exit 1
fi

# the CROP_POSITION will thansform above result to be: "470:165"

CROP_POSITION=$(
  echo "${CONNECTED_COMPONENT_RESULT}" | \
  jq --raw-input --raw-output --slurp \
  '[match("960x640[+](\\d+)[+](\\d+)").captures[].string] | join(":")'
)

# do crop video

ffmpeg -i "$BASENAME" -vf crop="960:640:${CROP_POSITION}" -c:a copy "$NO_EXT_BASENAME"-crop.mp4

# clean up

rm "${SCREENSHOT_PATH}" "${TMP_STDERR}"

Screenshot example: