Find all video of the series, trim splash screen for each of them, keep and reorder two audio streams and make first by default

video_cutter.sh

#!/usr/bin/env bash

source="/home/user/source"
target="/home/user/target"

find "$source" -type f -name "*.mkv" -print0 | while read -d $'\0' f; do
  name=$(basename "$f" .mkv)
  echo "$name"

  ss=$(ffprobe -i "$f" 2>&1 | grep "Chapter #0:1" | grep -Eo "[0-9.]+" | head -3 | tail +3)
  ss=$(echo $ss + 7 | bc)
  ffmpeg \
    -v error \
    -nostdin \
    -y \
    -i "$f" \
    -ss "$ss" \
    -map 0:v -c:v copy \
    -map 0:a:1 -c:a:0 copy \
    -map 0:a:0 -c:a:1 copy \
    -disposition:a:0 default \
    -async 1 \
    "$target/$name.mkv"
done

find "$source" -type f -name "*.mkv" -print0 | while read -d $'\0' f; do - just a fucking magic about find all video files and look up through each of them

ffprobe options:

• ffprobe -i "$f" 2>&1 - outputs information into stdout
• grep "Chapter #0:1" - find line with information about second chapter
• grep -Eo "[0-9.]+" - extract any numbers from the line and print each on own line
• head -3 - keep only first three lines
• tail +3 - skip first two lines

ss=$(echo $ss + 7 | bc) - I don't know why but ffmpeg starts to cut the video at ~7 seconds early than specified, so this is the correction

ffmpeg options:

• -v error - show only errors
• -nostdin - ignore any data from stdin
• -y - overwrite existent target files w/o any questions
• -i "$f" input file
• -ss "$ss" splash screen ends time
• -map 0:v -c:v copy - copy video stream from file #0 into output file
• -map 0:a:1 -c:a:0 copy - copy audio stream #1 from file #0 into stream #0 of output file
• -map 0:a:0 -c:a:1 copy - copy audio stream #0 from file #0 into stream #1 of output file
• -disposition:a:0 default - make audio stream #0 default
• -async 1 not sure about it, probably may be removed
• "$target/$name.mkv" - output file

If the stream disposition doesn't apply and first stream is remains default prepend this option with -disposition:s:0 0 that remove default disposition of the first stream.