Generate test-videos, black with white number, increases 1/frame

generate.sh

#!/bin/bash
set -euxo pipefail

FPS=(25 30)
CODEC=(libx264 nvenc_h264)

rm -f out*.mp4

for n in $(seq -f '%03.0f' 0 999); do
        [ -f "${n}.png" ] || convert \
                -size 1920x1080 \
                xc:black \
                -font 'DejaVu-Sans-Mono' \
                -pointsize 150 \
                -fill white \
                -gravity center \
                -draw "text 0,0 '${n}'" \
                "${n}.png"
done

for fps in "${FPS[@]}"; do
        for codec in "${CODEC[@]}"; do

                ffmpeg \
                        -f lavfi \
                        -i "anullsrc=channel_layout=stereo:sample_rate=44100" \
                        -framerate ${fps} \
                        -i %03d.png \
                        -c:v ${codec} \
                        -c:a aac \
                        -filter_complex "fps=${fps},format=yuv420p,loop=loop=100:size=1000:start=0" \
                        -g ${fps} \
                        -t 00:10:00.000 \
                        "out_${codec}_${fps}.mp4"

        done
done