yt-part.sh

#!/bin/bash

# Partial YouTube downloader (bash script for Windows).
# goncalomb (goncalomb.com), 2018

set -e
cd "$(dirname -- "$0")"

[ -f "youtube-dl.exe" ] || {
    echo "Downloading youtube-dl..."
    curl -ROL#C - "https://yt-dl.org/downloads/2018.09.18/youtube-dl.exe"
    echo
}

[ -f "ffmpeg.exe" ] || {
    echo "Downloading ffmpeg..."
    curl -ROL#C - "https://ffmpeg.zeranoe.com/builds/win64/static/ffmpeg-20180917-bd10c1e-win64-static.zip"
    unzip -jo ffmpeg-*.zip ffmpeg-20180917-bd10c1e-win64-static/bin/ffmpeg.exe
    echo
}

format_time() { echo "$1s" | sed -e 's/\(.*\):/\1m/' -e 's/\(.*\):/\1h/'; }

if [ -z "$1" ] || [ -z "$2" ] || [ -z "$3" ]; then
    echo "usage: $0 <youtube-url> <start> <duration> [-t]"
    echo "  -t transcode video for perfect slicing (slower)"
    echo "start/duration format: 00:00:00 (h:m:s) or 00:00 (m:s) or 00 (s)"
    exit
fi

DIR="videos"
mkdir -p "$DIR"

TRANSCODE=
CODEC="-c copy"
if [ "$4" == "-t" ]; then
    TRANSCODE="-transcoded"
    CODEC=""
else
    echo "Not transcoding! Video slicing may not be perfect, use -t to enable transcoding (slower)."
fi

echo "Fetching video urls..."
URLS=$(./youtube-dl.exe -g "$1")
URL_VIDEO=$(echo "$URLS" | sed '1q;d')
URL_AUDIO=$(echo "$URLS" | sed '2q;d')

echo "Fetching video name..."
FILENAME=$(./youtube-dl.exe --get-filename "$1")
FILENAME="$DIR/${FILENAME%.*}-$(format_time "$2")($(format_time "$3"))$TRANSCODE.mkv"

echo "Saving to '$FILENAME'..."
./ffmpeg.exe -hide_banner -loglevel info -y -ss "$2" -i "$URL_VIDEO" -ss "$2" -i "$URL_AUDIO" -t "$3" $CODEC -map "0:v:0" -map "1:a:0" "$FILENAME"

echo
echo "Saved '$FILENAME'."