Mux multiple subtitle files into an mp4 file

mp4_srt.py

# pip install sh pycountry
import re
from pathlib import Path

import pycountry
from sh import ffmpeg


def mux_mp4_subs(inp, outp, *subs, _cwd=None, **subs_map):
    """Mux multiple subtitle files into an mp4 file.

    Example:
        >>> mux_mp4_subs(
        ...     "original.mp4",
        ...     "original.subs.mp4",
        ...     "2_English.srt",
        ...     czech="Subs/4_Czech.srt",
        ... )
    """
    sub_files, sub_commands = [], []
    subs_map = {**{Path(sub).stem: sub for sub in subs}, **subs_map}
    for i, (lang, path) in enumerate(subs_map.items()):
        sub_files += ["-i", path]
        lang = "".join(re.findall("[a-z]+", lang.lower()))
        try:
            # https://en.wikibooks.org/wiki/FFMPEG_An_Intermediate_Guide/subtitle_options#Set_Subtitle_Language
            try:
                lang = pycountry.languages.lookup(lang).alpha_3
            except LookupError:
                lang = pycountry.countries.search_fuzzy(lang)[0].alpha_3.lower()
        except LookupError:
            pass
        sub_commands += ["-map", str(i + 1), f"-metadata:s:s:{i}", f"language={lang}"]
    try:
        # https://stackoverflow.com/questions/46521858/adding-multiple-srt-subtitle-streams-to-mp4-with-ffmpeg#comment129177458_65587372
        return ffmpeg(
            "-i",
            inp,
            *sub_files,
            *sub_commands,
            *"-map 0:v -map 0:a -c:v copy -c:a copy -c:s mov_text -movflags use_metadata_tags -map_metadata 0".split(),
            outp,
            _cwd=_cwd,
        )
    except Exception as exc:
        raise Exception(exc.stderr.decode())