Simple and dumb script to import the most important meta data to Quod Libet from SQLite. It was sufficient for me but might not be for you, for example it lacks a check for multiple artists. However I thought it might be helpful since the documentation for the Quod Libet python API is not great

import-sqlite-to-quodlibet.py

import quodlibet.library
from quodlibet.query import Query
from quodlibet import app
import sqlite3

# you need a Quod Libet dev environment
# this script and your QL songs file need to be placed at the root of your Quod Libet git checkout
# there is another one for copying QL data to SQLite https://gist.github.com/WildRikku/15b645d236b2d4edf32c01c9603a2c86

dbcon = sqlite3.connect("../songs.db")
dbcur = dbcon.cursor()

# realdata is the file you copied from your actual Quod Libet config dir
library = quodlibet.library.init('../realdata')
app.library = library

for song in Query('').filter(app.library):
	songDict = {}
	whereStr = []
	title = song.get('title', None),
	artist = song.get('artist', None),
	album = song.get('album', None),
	version = song.get('version', None)

	if title is not None and title[0] is not None:
		songDict['title'] = title[0]
		whereStr.append('title=:title')
	else:
		whereStr.append('title IS NULL')
	if artist is not None and artist[0] is not None:
		songDict['artist'] = artist[0]
		whereStr.append('artist=:artist')
	else:
		whereStr.append('artist IS NULL')
	if album is not None and album[0] is not None:
		songDict['album'] = album[0]
		whereStr.append('album=:album')
	else:
		whereStr.append('album IS NULL')
	if version is not None:
		songDict['version'] = version
		whereStr.append('version=:version')
	else:
		whereStr.append('version IS NULL')

	# ugh this is so inefficient, running a query for every song, but well, it works
	res = dbcur.execute(
		"SELECT playCount, skipCount, added, lastplayed, laststarted FROM songs_merged WHERE " + ' AND '.join(
			whereStr),
		songDict)
	data = res.fetchone()
	if data is not None:
		song['~#playcount'] = data[0]
		song['~#skipcount'] = data[1]
		song['~#added'] = data[2]
		song['~#lastplayed'] = data[3]
		song['~#laststarted'] = data[4]
	else:
		# for debugging only, set breakpoint to next line
		print(
			"SELECT playCount, skipCount, added, lastplayed, laststarted FROM songs_merged WHERE " + ' AND '.join(
				whereStr))

app.library.dirty = True
app.library.save()