Ugoira to mjpg mkv

import json, subprocess

with open('ugoira_meta.json') as f:
    data = json.load(f)
f.closed

with open('timestamps.txt', 'w') as f:
    f.write('# timestamp format v2\n')
    f.write('0\n')

    cur_time = 0

    for i in data['body']['frames']:
        cur_time += i['delay']
        f.write(str(cur_time)+"\n")

f.closed

print(subprocess.run(['ffmpeg',
                '-framerate',
                '30',
                '-i',
                '%06d.jpg',
                '-codec',
                'copy',
                'mjpg.mkv']))

print(subprocess.run(['mkvmerge',
                '-o',
                'ugoira.mkv',
                '-d',
                '0',
                '-A',
                '--timestamps',
                '0:timestamps.txt',
                'mjpg.mkv']))