fix: normalize YouTube URLs before passing to yt-dlp

Converts youtu.be short URLs to youtube.com/watch?v= format and strips
tracking/share parameters (si=, is=, feature=, etc.) that can confuse yt-dlp.

app/downloader.py

@@ -2,13 +2,41 @@ import asyncio
 import uuid
 import os
 from pathlib import Path
+from urllib.parse import urlparse, parse_qs, urlencode, urlunparse
 from app.config import settings
 
 AUDIO_TMP_DIR = "/tmp/apoena-audio"
 
+# Query parameters that are tracking/share metadata and not part of the video identity
+_STRIP_PARAMS = {"si", "is", "feature", "pp", "ab_channel"}
+
+
+def normalize_youtube_url(url: str) -> str:
+    """Normalize YouTube URLs to canonical form for yt-dlp compatibility.
+
+    Converts youtu.be short URLs to youtube.com/watch?v= and strips
+    tracking/share parameters (si=, is=, feature=, etc.).
+    """
+    parsed = urlparse(url)
+    netloc = parsed.netloc.lower()
+
+    if netloc in ("youtu.be", "www.youtu.be"):
+        video_id = parsed.path.lstrip("/")
+        if video_id:
+            return f"https://www.youtube.com/watch?v={video_id}"
+
+    if netloc in ("youtube.com", "www.youtube.com", "m.youtube.com"):
+        qs = parse_qs(parsed.query, keep_blank_values=True)
+        cleaned = {k: v for k, v in qs.items() if k not in _STRIP_PARAMS}
+        new_query = urlencode({k: v[0] for k, v in cleaned.items()})
+        return urlunparse(parsed._replace(netloc="www.youtube.com", query=new_query))
+
+    return url
+
 
 async def extract_audio(url: str) -> Path:
     """Download audio-only from a URL using yt-dlp. Returns path to an mp3 temp file."""
+    url = normalize_youtube_url(url)
     job_id = str(uuid.uuid4())
     outtmpl = f"{AUDIO_TMP_DIR}/{job_id}.%(ext)s"
     expected = Path(f"{AUDIO_TMP_DIR}/{job_id}.mp3")