download fragment of a youtube video without downloading the whole thing

yt-seek.sh

#!/bin/bash

NAME=yt-seek
if [ "$#" -ne 3 ]; then
    echo "Usage: $NAME <url> <start> <duration>"
    exit 1
fi

URL=$1
START=$2
DURATION=$3

AV=($(youtube-dl -g $URL))
if [ "${#AV[@]}" -ne 2 ]; then
    echo "Could not extract streams"
    exit 1
fi

AUDIO=${AV[0]}
VIDEO=${AV[1]}

ffmpeg -ss $START -i $VIDEO \
       -ss $START -i $AUDIO \
       -t $DURATION -c copy out.mp4