Self-contained OpenWRT crontab for IP camera records management

crontab

# #ffmpeg
# SECONDS=900
# DURATION=$(($(date "+$SECONDS-(%M%%15)*60-%S")))
## tcp transport ensures bottom half of frame is not pixelated
# PRE_IN="-t $DURATION -rtsp_transport tcp"
# LOGIN=
# PASSWORD=
# IP=
# IN=rtsp://$LOGIN${PASSWORD:+:$PASSWORD}@$IP:554/mpeg4
# START="$(date '+%Y%m%d_%H%M%S')"
# META="-metadata title=$START"
# FLAGS="-an -vcodec copy $META -bsf hevc_mp4toannexb -f mp4"
# OUT="/records/$START.mp4"
# PID=$(pgrep ffmpeg) && {
#   du -h "$(tr '\0' '\n' < /proc/$PID/cmdline | tail -1)" | logger -t ffmpeg
#   [ "$DURATION" -lt "$(($SECONDS-10))" ] && exit 0
# }
# logger -t ffmpeg ffmpeg $PRE_IN -i "$IN" $FLAGS "$OUT"
# exec ffmpeg $PRE_IN -i "$IN" $FLAGS "$OUT" #2> "${OUT%/*}/.${OUT##*/}.stderr"
## $'\43' works around busybox's logging of cron command only up to first #
* * * * * C=ffmpeg && H=$'\043' && crontab -l | sed -nre "/^$H $H$C/,/^$H exec $C /{s/^$H *//;p}" | sh > /dev/null 2>&1 &
# delete hour-sized batches once 90% disk usage is exceeded
1 * * * * D=/records && while df -P "$D" | awk '-F[ %]+' '{f=NR>1 && $5 > 90} END{exit 1-f}' && ls -1rtc "$D" | head -4 | xargs -t rm ; do true ; done