sample_from_youtube.bash

#!/usr/bin/env bash

function parse {
	awk '
	function trim(str) {
		# Remove leading and trailing whitespaces
		gsub(/^\s*/, "", str)
		gsub(/\s*$/, "", str)
		return str
	}

	BEGIN {
		FS = "|"
		OFS = ","
	}

	# A Comment:
	/^#/ {
		next
	}

	# Video link:
	/^-/ {
		if (NF != 2) {
			print "Check line", NR > "/dev/stderr"
			exit 1
		}

		first = substr($1, 2)

		record_name = first
		yt_url = $2

		record_name = trim(record_name)
		yt_url = trim(yt_url)
	}

	# Sample snippet:
	!/^-/ && !/^$/ {
		if (NF != 2) {
			print "Check line", NR > "/dev/stderr"
			exit 2
		}

		timestamps_string = $1 # Like "0:12 - 0:19"
		sample_name = $2

		timestamps_string = trim(timestamps_string)
		sample_name = trim(sample_name)

		if (split(timestamps_string, timestamps, "-") != 2) {
			print "Check line", NR > "/dev/stderr"
			exit 3
		}

		for (i in timestamps) {
			timestamps[i] = trim(timestamps[i])
		}

		filename = record_name "__" sample_name
		gsub(/ /, "_", filename)

		# Output format: filename, youtube url, start timestamp, end timestamp
		print filename, yt_url, timestamps[1], timestamps[2]
	}
	' "$1"
}

function skip_collected {
	while IFS=',' read -ra LINE
	do
		FNAME="${LINE[0]}"
		YT_URL="${LINE[1]}"
		START="${LINE[2]}"
		END="${LINE[3]}"

		if test -f "${SAMPLES_DIR}/${FNAME}.wav"
		then
			echo "Skipping \"$FNAME\", file already exists..." 1>&2
			continue
		fi

		echo $FNAME,$YT_URL,$START,$END
	done
}

function append_video_id {
	awk '
		BEGIN {
			FS=","
			OFS=","
		}

		{
			# Match video id in youtube url query string:
			idx = match($2, /(\?v|&v)[^&]*/)
			if (idx == 0 || RLENGTH - 3 != 11) {
				printf("Could not extract video id from %s for \"%s\", skipping\n", $2, $1) > "/dev/stderr"
				next
			}
			# +=3 because of "?v" or "&v" prefix:
			print $0, substr($2, RSTART + 3, RLENGTH - 3)
		}'
}

# NOTE: couldn't I have just deleted temp files with 'sample_from_youtube_downloaded_files_' prefix?
# answer: NO! what about other users who might be downloading samples in parallel (Really???)?
# NOTE: I could also have made per-process unique prefix...
DOWNLOADED_FILES=$(mktemp -t "sample_from_youtube_downloaded_files_XXXXXXX")
trap "(cat $DOWNLOADED_FILES | xargs -r rm) && rm $DOWNLOADED_FILES" EXIT

function download_audio {
	declare -A id_to_file

	while IFS=',' read -ra LINE
	do
		FNAME="${LINE[0]}"
		YT_URL="${LINE[1]}"
		START="${LINE[2]}"
		END="${LINE[3]}"
		YT_ID="${LINE[4]}"

		if test -n "${id_to_file[$YT_ID]}"
		then
			TMPFILE="${id_to_file[$YT_ID]}"
		else
			TMPFILE=$(mktemp -t "sample_from_youtube_${YT_ID}_XXXXX.wav")

			echo "Starting $YT_ID download..." 1>&2
			youtube-dl \
				--no-cache-dir \
				--quiet \
				--no-continue \
				--no-playlist \
				--extract-audio \
				--audio-format wav \
				--audio-quality 0 \
				--output "$TMPFILE" \
				"$YT_URL"
			youtube_dl_status="$?"
			if test 0 == "$youtube_dl_status"
			then
				echo "Downloading $YT_ID complete." 1>&2
			else
				echo "Failed to download $YT_ID. `youtube-dl` exit status: $youtube_dl_status" 1>&2
				continue
			fi

			echo $TMPFILE >> $DOWNLOADED_FILES
			id_to_file[$YT_ID]=$TMPFILE
		fi

		echo $FNAME,$TMPFILE,$START,$END

	done
}

function crop_sample {
	while IFS=',' read -ra LINE
	do
		FNAME="${LINE[0]}"
		AUDIO_FILE="${LINE[1]}"
		START="${LINE[2]}"
		END="${LINE[3]}"

		# TODO: $END needs +1 second.
		ffmpeg \
			-nostdin \
			-i "$AUDIO_FILE" \
			-ss "$START" \
			-to "$END" \
			-n \
			-loglevel "quiet" \
			"${SAMPLES_DIR}/${FNAME}.wav" \
			2>/dev/null
		if test 0 == $?
		then
			echo "Done: ${FNAME}.wav"
		else
			echo "There was an error with ${FNAME}.wav"
		fi
	done
}

if ! command -v youtube-dl 1>/dev/null
then
	echo "Please install youtube-dl first!" 1>&2
	exit 1
fi

USAGE="Usage: $(basename "$0") [-h] [-s samples_file] [-o output_directory]"

while getopts ":s:o:h" opt; do
	case ${opt} in
		h)
			echo "$USAGE"
			exit 0
			;;
		s)
			SAMPLES=$OPTARG
			;;
		o)
			SAMPLES_DIR=$OPTARG
			;;
		\?)
			echo "Invalid option: -$OPTARG" 1>&2
			echo "$USAGE" 1>&2
			exit 1
			;;
		:)
			echo "Invalid option: -$OPTARG requires an argument" 1>&2
			echo "$USAGE" 1>&2
			exit 1
			;;
	esac
done
shift $((OPTIND-1))

SAMPLES=${SAMPLES:-~/samples}
SAMPLES_DIR=${SAMPLES_DIR:-~/samples.out}
mkdir -p "$SAMPLES_DIR"

parse $SAMPLES \
	| skip_collected \
	| append_video_id \
	| download_audio \
	| crop_sample