---
title: "yt-dlp YouTube JS Challenge Fix (Fedora)"
domain: troubleshooting
category: general
tags: [yt-dlp, fedora, youtube, javascript, deno]
status: published
created: 2026-04-02
updated: 2026-04-02
---
# yt-dlp YouTube JS Challenge Fix (Fedora)

## Problem

When running `yt-dlp` on Fedora, downloads may fail with the following warnings and errors:

```
WARNING: [youtube] No supported JavaScript runtime could be found.
WARNING: [youtube] [jsc:deno] Challenge solver lib script version 0.3.2 is not supported (supported version: 0.4.0)
WARNING: [youtube] 0qhgPKRzlvs: n challenge solving failed: Some formats may be missing.
ERROR: Did not get any data blocks
ERROR: fragment 1 not found, unable to continue
```

This causes subtitle downloads (and sometimes video formats) to fail silently, with the MP4 completing but subtitles being skipped.

### Root Causes

1. **No JavaScript runtime installed** — yt-dlp requires Deno or Node.js to solve YouTube's JS challenges
2. **Outdated yt-dlp** — the bundled challenge solver script is behind the required version
3. **Remote challenge solver not enabled** — the updated solver script must be explicitly fetched

---

## Fix

### 1. Install Deno

Deno is not in the Fedora repos. Install via the official installer:

```bash
curl -fsSL https://deno.land/install.sh | sh
sudo mv ~/.deno/bin/deno /usr/local/bin/deno
deno --version
```

> Alternatively, Node.js works and is available via `sudo dnf install nodejs`.

### 2. Update yt-dlp

```bash
sudo pip install -U yt-dlp --break-system-packages
```

> If installed via standalone binary: `yt-dlp -U`

### 3. Enable Remote Challenge Solver

Add `--remote-components ejs:github` to the yt-dlp command. This fetches the latest JS challenge solver from GitHub at runtime:

```bash
yt-dlp -f 'bestvideo[vcodec^=avc]+bestaudio[ext=m4a]/bestvideo+bestaudio' \
  --merge-output-format mp4 \
  -o "/plex/plex/%(title)s.%(ext)s" \
  --write-auto-subs --embed-subs \
  --remote-components ejs:github \
  https://www.youtube.com/watch?v=VIDEO_ID
```

### 4. Persist the Config

Create a yt-dlp config file so `--remote-components` is applied automatically:

```bash
mkdir -p ~/.config/yt-dlp
echo '--remote-components ejs:github' > ~/.config/yt-dlp/config
```

---

## Maintenance

YouTube pushes extractor changes frequently. Keep yt-dlp current:

```bash
sudo pip install -U yt-dlp --break-system-packages
```

---

## Known Limitations

### n-Challenge Failure: "found 0 n function possibilities"

Even with Deno installed, the remote solver downloaded, and yt-dlp up to date, some YouTube player versions can still fail n-challenge solving:

```
WARNING: [youtube] [jsc] Error solving n challenge request using "deno" provider:
Error running deno process (returncode: 1): error: Uncaught (in promise)
"found 0 n function possibilities".
WARNING: [youtube] n challenge solving failed: Some formats may be missing.
ERROR: [youtube] Requested format is not available.
```

This is a known upstream issue tied to specific YouTube player builds (e.g. `e42f4bf8`). It is not fixable locally — it requires a yt-dlp patch when YouTube rotates the player.

**Workaround:** Use a permissive format fallback instead of forcing AVC:

```bash
yt-dlp -f 'bestvideo+bestaudio/best' \
  --merge-output-format mp4 \
  -o "/plex/plex/%(title)s.%(ext)s" \
  --write-auto-subs --embed-subs \
  --remote-components ejs:github \
  https://www.youtube.com/watch?v=VIDEO_ID
```

This lets yt-dlp pick the best available format rather than failing on a missing AVC stream. To inspect what formats are actually available:

```bash
yt-dlp --list-formats --remote-components ejs:github \
  https://www.youtube.com/watch?v=VIDEO_ID
```

### HTTP 429 Too Many Requests + Impersonation Warning

Downloads or subtitle fetches fail with:

```
WARNING: The extractor specified to use impersonation for this download,
but no impersonate target is available.
ERROR: Unable to download video subtitles for 'en-en-US': HTTP Error 429: Too Many Requests
```

**Cause:** yt-dlp needs `curl_cffi` to impersonate a real browser's TLS fingerprint. Without it, YouTube detects the non-browser client and rate-limits with 429s. Subtitle downloads are usually the first to fail.

**Fix:**

```bash
pip3 install --upgrade yt-dlp curl_cffi
```

Once `curl_cffi` is installed, yt-dlp automatically uses browser impersonation and the 429s stop. No config changes needed.

### SABR-Only Streaming Warning

Some videos may show:

```
WARNING: [youtube] Some android_vr client https formats have been skipped as they
are missing a URL. YouTube may have enabled the SABR-only streaming experiment.
```

This is a YouTube-side experiment. yt-dlp falls back to other clients automatically — no action needed.

### pip Version Check

`pip show` does not accept `--break-system-packages`. Run separately:

```bash
yt-dlp --version
pip show yt-dlp
```

### Format Not Available: Strict AVC+M4A Selector

The format selector `bestvideo[vcodec^=avc]+bestaudio[ext=m4a]` will hard-fail if YouTube doesn't serve H.264 (AVC) video for a given video:

```
ERROR: [youtube] Requested format is not available. Use --list-formats for a list of available formats
```

This is separate from the n-challenge issue — the format simply doesn't exist for that video (common with newer uploads that are VP9/AV1-only).

**Fix 1 — Relax the selector to mp4 container without enforcing codec:**

```bash
yt-dlp -f 'bestvideo[ext=mp4]+bestaudio[ext=m4a]/bestvideo+bestaudio' \
  --merge-output-format mp4 \
  -o "/plex/plex/%(title)s.%(ext)s" \
  --write-auto-subs --embed-subs \
  https://youtu.be/VIDEO_ID
```

**Fix 2 — Let yt-dlp pick best and re-encode to H.264 via ffmpeg (Plex-safe, slower):**

```bash
yt-dlp -f 'bestvideo+bestaudio' \
  --merge-output-format mp4 \
  --recode-video mp4 \
  -o "/plex/plex/%(title)s.%(ext)s" \
  --write-auto-subs --embed-subs \
  https://youtu.be/VIDEO_ID
```

Use `--recode-video mp4` when Plex direct play is required and the source stream may be VP9/AV1. Requires ffmpeg.

**Inspect available formats first:**

```bash
yt-dlp --list-formats https://youtu.be/VIDEO_ID
```