timelens.sh

#!/bin/bash

set -e

INFILE="rc3-mcr-11512-eng-deu-CIA_vs_Wikileaks_hd.mp4"
OUTDIR="output/"
FRAMES=1000



tmpdir="$(mktemp -d)"

framecount=$(ffprobe -v error -select_streams v:0 -show_entries stream=nb_frames -of default=nokey=1:noprint_wrappers=1 "${INFILE}")
nthframe=$((framecount/FRAMES))
duration=$(echo "$(ffprobe -v error -select_streams v:0 -show_entries stream=duration -of default=nokey=1:noprint_wrappers=1 "${INFILE}") * 1000" | bc -l | cut -d'.' -f1)
framedur=$((duration/FRAMES))

ffmpeg -i "${INFILE}" -filter_complex "[v] select=not(mod(n\,${nthframe})) [frames]; [frames] scale=160:-1 [scaled]" -map '[scaled]' -vsync vfr -compression_algo raw -pix_fmt rgb24 -vframes 1000 "${tmpdir}/%04d.tiff"

width=$(identify -format "%w" "${tmpdir}/0001.tiff")
height=$(identify -format "%h" "${tmpdir}/0001.tiff")

montage "${tmpdir}"/*.tiff -tile 6x11 -geometry '+0x+0' "${OUTDIR}/frames-%d.jpg"
montage "${tmpdir}"/*.tiff -tile x1 -geometry 1x90'!' "${OUTDIR}/timeline.jpg"

print_timestamp() {
	minutes=$(((${1}/1000)/60))
	seconds=$(((${1}/1000)%60))
	hundreds=$((${1}%1000))
	printf "%02d:%02d.%03d" ${minutes} ${seconds} ${hundreds}
}

(
	echo "WEBVTT"
	echo ""
	lasttimestamp=0
	for i in $(seq 0 $((FRAMES-1))); do
		row=$(((i%66)/6))
		col=$(((i%66)%6))
		timestamp=$((lasttimestamp+framedur))
		echo "$(print_timestamp ${lasttimestamp}) --> $(print_timestamp ${timestamp})"
		echo "frames-$((i/66)).jpg?xywh=$((width*col)),$((height*row)),${width},${height}"
		echo ""
		lasttimestamp=$timestamp
	done
)> "${OUTDIR}/timelens.vtt"

rm -r "${tmpdir}"