Convert TTML2 subtitles (https://www.w3.org/TR/2021/CR-ttml2-20210309/) to SRT (https://en.wikipedia.org/wiki/SubRip)

ttml2-to-srt.py

#!/usr/bin/env python3

# DEPENDENCIES
#     pip3 install srt lxml

# TTML2 to SRT subtitle converter
# USAGE:
#   ttml2srt.py matrix.ttml2

import sys
import xml.etree.ElementTree as ET
from pathlib import Path

import srt
from lxml import etree
from srt import srt_timestamp_to_timedelta


def to_string(tree):
    return etree.tostring(tree, pretty_print=True)


if __name__ == '__main__':

    subs = []
    i = 0

    root = ET.parse(sys.argv[1])
    nodes = root.findall('//{http://www.w3.org/ns/ttml}p')

    for node in nodes:
        start = srt_timestamp_to_timedelta(node.attrib['begin'])
        end = srt_timestamp_to_timedelta(node.attrib['end'])
        text = node.text
        i += 1
        subs.append(srt.Subtitle(index=i, start=start, end=end, content=text))

    all_subs = srt.compose(subs)
    print(all_subs)

    output_file = Path(sys.argv[1]).with_suffix('.srt')
    with open(output_file, 'w', encoding='utf8') as fo:
        fo.write(all_subs)
        print(f"Wrote file {output_file}")