Video utils

Video Subtitles

This tutorial explains how to add subtitles to the video files.

Prepare

Install:

sudo apt install qnapi uchardet ffmpeg recode

Download subtitles for your language

Qnapi

qnapi -l pl *.mp4
qnapi -l pl *.mkv

VLsub

or open with VLC, with VLsub extension.

Subliminal

pip install subliminal
subliminal download -l pl *.mkv

Detect encoding

uchardet *.txt

Expect UTF-8, Windows-1250 or UTF-16.

Verify that converted encoding is actually fine

cat *.txt | recode cp1250..utf8
cat *.txt | recode utf16..utf8

Available encodings:

recode --list

Recode to UTF8

recode cp1250..utf8 *.txt
# or
recode utf16..utf8 *.txt

Convert to SRT

Convert TXT to SRT, add .default.srt suffix for Jellyfin:

ffmpeg -i 'S01E03.txt' 'S01E03.default.srt'

ls -1 *.txt | sed -e 's/\.txt$//g' | xargs -d '\n' -I %s echo 'ffmpeg -i "%s.txt" "%s.default.srt"'

Appendix

Do the ffmpeg conversion for all TXT files in the current directory:

from pathlib import Path
from nuclear import shell

for path in Path('.').iterdir():
    if path.name.endswith('.txt'):
        stem = path.name[:-4]
        print(f'converting {path.name}')
        shell(f"ffmpeg -i '{stem}.txt' '{stem}.default.srt'")

Download YouTube video as MP4

pip install -U yt-dlp
yt-dlp -f 'bestvideo[height<=1080][ext=mp4]+bestaudio[ext=m4a]/best[ext=mp4]/best' URL

Dynamic Audio Normalizer

This allows for applying extra gain to the "quiet" sections of the audio while avoiding distortions or clipping the "loud" sections. In other words: The Dynamic Audio Normalizer will "even out" the volume of quiet and loud sections, in the sense that the volume of each section is brought to the same target level.

ffmpeg -i "$INPUT.mkv" -c:v copy -af "dynaudnorm=maxgain=30" -c:a aac -b:a 192k "$INPUT.norm.mkv"

ls -1 *.mkv | sed -e 's/\.mkv$//g' | xargs -d '\n' -I %s echo 'ffmpeg -i "%s.mkv" -c:v copy -af "dynaudnorm=maxgain=30" -c:a aac -b:a 192k "%s.norm.mkv"'
ls -1 *.mp4 | sed -e 's/\.mp4$//g' | xargs -d '\n' -I %s echo 'ffmpeg -i "%s.mp4" -c:v copy -af "dynaudnorm=maxgain=30" -c:a aac -b:a 192k "%s.norm.mp4"'

Extract normalized audio from video:

ffmpeg -i input.mkv -map a \
    -filter:a "pan=stereo|FL < 1.0*FL + 0.707*FC + 0.707*BL|FR < 1.0*FR + 0.707*FC + 0.707*BR" \
    -filter:a "aresample=matrix_encoding=dplii" \
    -filter:a "dynaudnorm=maxgain=50:framelen=400:gausssize=15" \
    -ac 2 -q:a 0 \
    output.mp3

Split video into chunks

#!/usr/bin/env -S uv run --script
# /// script
# dependencies = [
#   "nuclear",
# ]
# ///
from nuclear import shell, logger
from pathlib import Path

src_path = '[INPUT_PATH].mkv'
dst_suffix = '-[TITLE].mkv'
chunk_duration = 10  # in minutes

def format_duration_m(minutes: int) -> str:
    return f"{minutes // 60}:{minutes % 60}:00"

src_duration_s = float(shell(f'ffprobe -v error -show_entries format=duration -of default=noprint_wrappers=1:nokey=1 "{src_path}"').strip())
parts = list(range(0, int(src_duration_s // 60), chunk_duration))
logger.debug('Creating chunks', parts=parts, count=len(parts))
for index, part in enumerate(parts):
    minutes_from = part
    minutes_to = part + chunk_duration
    out_path = f'{str(index+1).zfill(3)}{dst_suffix}'
    shell(
        f'ffmpeg'
        f' -i "{src_path}"'
        f' -ss {format_duration_m(minutes_from)} -to {format_duration_m(minutes_to)}'
        f' -c:v copy'
        f' -filter:a "pan=stereo|FL < 1.0*FL + 0.707*FC + 0.707*BL|FR < 1.0*FR + 0.707*FC + 0.707*BR"'  # Downmix to stereo
        f' -filter:a "aresample=matrix_encoding=dplii"'
        f' -filter:a "dynaudnorm=maxgain=50:framelen=400:gausssize=15"'  # Dynamic audio normalization
        f' -ac 2 -c:a aac -b:a 192k'
        f' "{out_path}"'
    )
    logger.info(f'Created: {out_path}')