YouTube - MP4 to MP3 messes up - node.js

Question

It's supposed to download all the videos in the playlist and convert them to mp3. But all this does is make the mp4's and 1 empty mp3 with a number higher than the max mp4. My newbie brain doesn't know how to fix this...
var ytpl = require('ytpl');
var fs = require('fs-extra');
var path = require('path');
var ffmpeg = require('fluent-ffmpeg');
var binaries = require('ffmpeg-static');
var ytdl = require('ytdl-core');
var output_dir = path.join(__dirname+"/dl");
ytpl("PL8n8S4mVUWvprlN2dCAMoIo6h47ZwR_gn", (err, pl) => {
if(err) throw err;
let c = 0;
pl.items.forEach((i) => {
ytdl(i.url_simple+"", { filter: 'audioonly' }).pipe(fs.createWriteStream(output_dir+"/"+c+".mp4")).on('finish', () => {
console.log("Finished MP4 DL, starting conversion...");
ffmpeg(output_dir+"/"+c+".mp4")
.setFfmpegPath(binaries.path)
.format('mp3')
.audioBitrate(320)
.output(fs.createWriteStream(output_dir+"/"+c+".mp3"))
.on('end', () => {
console.log("Finished MP3 Convert...");
})
.run();
});
c++;
});
});

Answer 1

Fixed using an example by ytdl-core Link
Fixed code:
var ytpl = require('ytpl');
var fs = require('fs-extra');
var path = require('path');
var ffmpeg = require('fluent-ffmpeg');
var binaries = require('ffmpeg-static');
var sanitize = require('sanitize-filename');
var ytdl = require('ytdl-core');
var output_dir = path.join(__dirname+"/dl");
ytpl("PL8n8S4mVUWvprlN2dCAMoIo6h47ZwR_gn", (err, pl) => {
if(err) throw err;
for (const i of pl.items) {
let stream = ytdl(i.id, {
filter: 'audioonly'
});
ffmpeg(stream)
.audioBitrate(320)
.save(`${output_dir}/${sanitize(i.title + " (by " + i.author.name + ")")}.mp3`)
.on('end', () => {
console.log("Done! Downloaded \""+i.title + " (by " + i.author.name + ")"+"\"");
});
}
});