Add download preview flow and search fallback

worker/downloader.py

@@ -5,6 +5,7 @@ import os
 import subprocess
 import sys
 import tempfile
+from typing import List
 
 
 def emit(status, progress, message="", output=""):
@@ -25,14 +26,74 @@ def run(cmd):
     return proc
 
 
+def parse_duration(value):
+    if value is None:
+        return "00:00:10"
+    total = int(float(value))
+    hours = total // 3600
+    minutes = (total % 3600) // 60
+    seconds = total % 60
+    return f"{hours:02d}:{minutes:02d}:{seconds:02d}"
+
+
+def format_label(height, ext):
+    if height:
+        return f"{height}p ({ext})"
+    return f"Best ({ext})"
+
+
+def build_quality_options(formats: List[dict]):
+    heights = []
+    for item in formats:
+        height = item.get("height")
+        if isinstance(height, int) and height > 0:
+            heights.append(height)
+
+    unique_heights = sorted(set(heights))
+    options = [{"value": "best", "label": "Best available"}]
+    for height in unique_heights:
+        options.append(
+            {
+                "value": f"bestvideo[height<={height}]+bestaudio/best[height<={height}]",
+                "label": f"Up to {height}p",
+            }
+        )
+    return options
+
+
+def probe(url):
+    cmd = ["yt-dlp", "--dump-single-json", "--no-playlist", url]
+    proc = run(cmd)
+    payload = json.loads(proc.stdout)
+    thumbnail = payload.get("thumbnail") or ""
+    duration = payload.get("duration")
+    formats = payload.get("formats") or []
+    preview = {
+        "title": payload.get("title") or "Untitled",
+        "thumbnail": thumbnail,
+        "durationSeconds": duration or 0,
+        "duration": parse_duration(duration),
+        "startDefault": "00:00:00",
+        "endDefault": parse_duration(duration),
+        "qualities": build_quality_options(formats),
+    }
+    print(json.dumps(preview), flush=True)
+
+
 def main():
     parser = argparse.ArgumentParser()
+    parser.add_argument("--mode", choices=["probe", "download"], default="download")
     parser.add_argument("--url", required=True)
     parser.add_argument("--start", default="00:00:00")
     parser.add_argument("--end", default="00:00:10")
     parser.add_argument("--output", required=True)
+    parser.add_argument("--quality", default="best")
     args = parser.parse_args()
 
+    if args.mode == "probe":
+        probe(args.url)
+        return
+
     os.makedirs(os.path.dirname(args.output), exist_ok=True)
     emit("starting", 5, "Resolving media stream")
 
@@ -42,7 +103,7 @@ def main():
             "yt-dlp",
             "--no-playlist",
             "-f",
-            "mp4/bestvideo*+bestaudio/best",
+            args.quality,
             "-o",
             source_path,
             args.url,