Does Jellyfin Play FLAC? Yes, and When It Doesn't

The short answer

Yes — Jellyfin plays FLAC. The server has handled it for years, and most modern clients (the web player, Finamp, Symfonium, Feishin, the desktop apps) will Direct Play a FLAC file: no conversion, no quality loss, bit-for-bit what is on disk.

So if you are asking "does Jellyfin support FLAC" before committing a music library to it — it does. Rip away.

Where it gets messy is transcoding. FLAC is only effortless when the client can take it as-is. The moment something forces the server to convert on the fly, you are relying on a much less well-trodden path, and that is where the reports of silence, stutter and pinned CPU come from. The usual triggers:

• A client that can't decode FLAC — some older browsers, some TV and car-stereo apps, and a fair few DLNA renderers. The server transcodes to something they understand, and quality and CPU both take the hit.
• FLAC as the audio track of a video file. This is the one that bites people: when the video gets transcoded, the FLAC audio path has historically been the flaky part, and "video plays, audio is silent" is a known failure mode on some clients.
• Channel or sample-rate mismatches — pushing a 5.1 or 24-bit/192 kHz track at a stereo device forces a conversion even when the codec itself is supported.
• Thin server hardware. Audio transcoding is cheap next to video, but a low-power NAS serving several streams will still feel it.

Which is a long way of saying: FLAC is the right format to store, and a sometimes-awkward format to stream to whatever random device you happen to be holding. That gap is exactly what sent me down the rabbit hole below — I got tired of one particular device choking, and built a stupidly simple converter instead of fighting the transcoder.

---

The build story

Let me paint you a picture. I'm running a Jellyfin media server (because I like my stuff local, thank you very much), and everything was smooth—until I threw some FLAC files at it. Cue the buffering, crashing, and a whole bunch of "Why won't this work?!" moments. Turns out, Jellyfin + FLAC isn't always a match made in heaven, especially on less beefy hardware.

So what did I do? Built my own freakin' web app to fix it.

The Problem: FLAC Drama in Jellyfin

Jellyfin’s a fantastic media server, but FLAC files, especially in larger libraries, can be a bit much. My setup was running on an AlmaLinux 9 VM, already handling torrent duties and some other lightweight services. I wanted something that could convert FLAC to MP3 or WAV—cleanly, quickly, and ideally via a simple web interface so I didn’t have to mess with the command line every time.

The Solution: A Custom DIY Audio Converter Web App

I didn’t want bloat. I didn’t want another media manager. I wanted a focused tool that just... converts audio. So I built a Flask-based web app, wrapped it in Gunicorn, and turned it into a systemd service. It’s lightweight, fast, and looks great with a dark pastel theme.

Features I Needed (and Got):

• Upload audio files via web UI
• Convert to MP3, WAV, or AAC using FFmpeg
• Save converted files directly to my mounted network storage
• Automatically delete the uploaded original files after conversion
• Provide real-time logging of conversion status via the web UI
• Modern interface with dark pastel colors (yes, vibes matter)
• Runs as a persistent background service
• Minimal resource usage
• Accessible from any device on my LAN
• Supports batch/multi-file uploads

Tech Stack

• Python 3 + Flask – For the core web server
• FFmpeg – Does the actual heavy lifting for conversion
• Gunicorn – A production-ready WSGI server
• systemd – To manage the service reliably across reboots
• AlmaLinux 9 MusicServ – Running as a VM in my home lab

Step-by-Step: Full Reproducible Setup with Code

1. Install Dependencies

sudo dnf install epel-release -y
sudo dnf install ffmpeg python3 python3-pip nginx -y
pip3 install --user flask gunicorn

2. Directory Layout

/opt/audio_converter/
├── app.py
├── run_gunicorn.sh
├── uploads/
├── templates/
│   └── index.html
└── static/
    ├── css/style.css
    └── js/main.js

3. app.py

from flask import Flask, request, render_template, Response, stream_with_context
import os, subprocess, time
from werkzeug.utils import secure_filename

BASE_DIR = os.path.dirname(os.path.abspath(__file__))
UPLOAD_FOLDER = os.path.join(BASE_DIR, 'uploads')
STORAGE_PATH = "/mnt/media_storage/audio_converted"
ALLOWED_EXTENSIONS = {'mp3', 'flac', 'aac', 'wav', 'ogg', 'm4a'}

app = Flask(__name__, static_folder='static', template_folder='templates')
app.config['UPLOAD_FOLDER'] = UPLOAD_FOLDER

os.makedirs(UPLOAD_FOLDER, exist_ok=True)
os.makedirs(STORAGE_PATH, exist_ok=True)

def allowed_file(filename):
    return '.' in filename and filename.rsplit('.', 1)[1].lower() in ALLOWED_EXTENSIONS

def convert_file(input_path, output_path):
    subprocess.run(['ffmpeg', '-y', '-i', input_path, output_path],
                   stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL)

@app.route('/')
def index():
    return render_template('index.html')

@app.route('/convert_stream', methods=['POST'])
def convert_stream():
    files = request.files.getlist('audiofiles')
    output_format = request.form.get('format')

    @stream_with_context
    def generate():
        for file in files:
            if file and allowed_file(file.filename):
                filename = secure_filename(file.filename)
                input_path = os.path.join(app.config['UPLOAD_FOLDER'], filename)
                file.save(input_path)

                yield f"data: 📥 Received: {filename}\n\n"
                time.sleep(0.2)

                base = os.path.splitext(filename)[0]
                output_filename = f"{base}.{output_format}"
                output_path = os.path.join(STORAGE_PATH, output_filename)

                yield f"data: 🔄 Converting to {output_format.upper()}...\n\n"
                convert_file(input_path, output_path)
                time.sleep(0.2)

                yield f"data: 📤 Saved to storage: {output_filename}\n\n"

                os.remove(input_path)
                yield f"data: 🧹 Deleted original: {filename}\n\n"
                time.sleep(0.1)

        yield "data: ✅ All files converted and uploaded!\n\n"

    return Response(generate(), mimetype='text/event-stream')

if __name__ == "__main__":
    app.run(host="0.0.0.0", port=5000)

4. run_gunicorn.sh

#!/bin/bash
source ~/.bashrc
/home/rzasharp/.local/bin/gunicorn -w 1 -t 600 -b 0.0.0.0:8000 app:app

5. templates/index.html

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Audio Converter</title>
  <link rel="stylesheet" href="/static/css/style.css">
  <meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
</head>
<body>
  <div class="container">
    <h1>🎧 Audio Converter</h1>
    <form id="uploadForm" enctype="multipart/form-data" method="POST" action="/convert_stream">
      <input type="file" name="audiofiles" multiple required>
      <select name="format">
        <option value="mp3">MP3</option>
        <option value="wav">WAV</option>
        <option value="aac">AAC</option>
      </select>
      <button type="submit">Convert & Upload</button>
    </form>
    <div id="statusBox" class="status"></div>
  </div>
  <script src="/static/js/main.js"></script>
</body>
</html>

6. static/css/style.css

body {
  margin: 0;
  font-family: 'Segoe UI', sans-serif;
  background-color: #1E1E2F;
  color: #ECECEC;
}

.container {
  max-width: 600px;
  margin: 50px auto;
  padding: 20px;
  background-color: #2C2C3E;
  border-radius: 12px;
  box-shadow: 0 0 20px rgba(0,0,0,0.5);
}

h1 {
  color: #A29BFE;
  text-align: center;
}

input[type="file"], select, button {
  width: 100%;
  padding: 10px;
  margin-top: 15px;
  border: none;
  border-radius: 6px;
  font-size: 1em;
}

select {
  background-color: #2C2C3E;
  color: #ECECEC;
}

button {
  background-color: #74B9FF;
  color: #1E1E2F;
  cursor: pointer;
  transition: background-color 0.3s;
}

button:hover {
  background-color: #81ECEC;
}

.status {
  height: 200px;
  overflow-y: auto;
  white-space: pre-line;
  font-family: monospace;
  background: #11182f;
  border: 1px solid #2c2c3e;
  border-radius: 6px;
  margin-top: 20px;
  padding: 10px;
}

7. static/js/main.js

document.getElementById("uploadForm").addEventListener("submit", function (e) {
  e.preventDefault();

  const form = e.target;
  const statusBox = document.getElementById("statusBox");
  statusBox.innerHTML = "";

  const formData = new FormData(form);

  fetch('/convert_stream', {
    method: 'POST',
    body: formData
  }).then(response => {
    const reader = response.body.getReader();
    const decoder = new TextDecoder("utf-8");

    function read() {
      reader.read().then(({ done, value }) => {
        if (done) return;

        const chunk = decoder.decode(value, { stream: true });
        chunk.split("\n\n").forEach(line => {
          if (line.startsWith("data: ")) {
            const msg = line.replace("data: ", "").trim();
            if (msg) {
              statusBox.innerHTML += msg + "<br/>";
              statusBox.scrollTop = statusBox.scrollHeight;
            }
          }
        });

        read();
      });
    }

    read();
  });
});

8. systemd service (optional)

[Unit]
Description=Flask Audio Converter Service
After=network.target

[Service]
User=rzasharp
WorkingDirectory=/opt/audio_converter
ExecStart=/opt/audio_converter/run_gunicorn.sh
Environment="PATH=/home/rzasharp/.local/bin:/usr/bin:/bin"
Restart=always

[Install]
WantedBy=multi-user.target

Then:

sudo systemctl daemon-reload
sudo systemctl enable --now audio_converter

Boom. Now it auto-starts on reboot and runs quietly in the background like a good little daemon.

Issues I Ran Into

• FLASK ONLY BINDING TO LOCALHOST: It was running on 127.0.0.1 and not accessible from other devices. Fixed it by using host='0.0.0.0'.
• Permission Errors: Flask couldn’t write to the upload folder. A quick chown -R to my user solved that.
• systemd wouldn’t launch gunicorn: Turned out gunicorn was in my .local/bin, which systemd doesn’t see by default. Fixed it by wrapping in a shell script.
• Wanting to delete originals: Added a checkbox and Python logic to remove original files post-conversion.

Resource Usage

Ridiculously light. We're talking ~1–2% CPU when converting and ~60MB RAM. It’s perfect to run alongside torrents or other lightweight tools on a low-resource VM.

Why I Love This

• I don’t have to think about it anymore.
• Anyone on my network can convert files (yes, you can add auth later).
• It just works—and it looks damn good doing it.

---

If you’re running Jellyfin or any other media server that chokes on FLAC or lossless audio formats, this setup is gold. Total time to build and debug everything? Around 4 hours. Clean. Simple. Reusable. Efficient.