Pin all yt-dlp calls to tv_embedded client to stop IP rate limiting

Without a player_client, yt-dlp probes web+mweb+android+tv in sequence
for every request, multiplying API calls ~4x and triggering YouTube IP
blocks. tv_embedded exposes the full format list in one shot and is the
least restricted client for authenticated sessions.

Applies to: search, trending, video/channel metadata, playlists, subs,
comments, and downloads — every yt-dlp invocation site.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/services/ytdlp.py

@@ -55,6 +55,12 @@ _meta_lock = threading.Lock()
 _meta_last_call: float = 0.0
 _META_MIN_GAP = 12.0  # seconds between any two metadata requests
 
+# Pin to tv_embedded client — it exposes full format list without SABR
+# restrictions and makes exactly ONE set of API requests per operation.
+# Without this yt-dlp probes web + mweb + android + tv in sequence,
+# multiplying requests and triggering YouTube IP rate limits.
+_YT_CLIENT = ["--extractor-args", "youtube:player_client=tv_embedded"]
+
 # Active download counter — _meta_run pauses while any download is running so
 # background discovery and a concurrent download never share the YouTube session
 # at the same time. Downloads set/clear this; _meta_run reads it.
@@ -211,6 +217,7 @@ def search_youtube(query: str, max_results: int = 40, polite: bool = False) -> l
         "--dump-json",
         "--flat-playlist",
         "--quiet",
+        *_YT_CLIENT,
         *_cookie_args(),
     ], timeout=60)
 
@@ -259,6 +266,7 @@ def fetch_trending(region: str = "US", max_results: int = 50) -> list[dict]:
         "--flat-playlist",
         "--quiet",
         "--playlist-end", str(max_results),
+        *_YT_CLIENT,
         *_cookie_args(),
     ], timeout=60)
 
@@ -309,6 +317,7 @@ def fetch_video_metadata(video_id: str, polite: bool = False) -> dict | None:
     base_cmd = [
         "yt-dlp", url,
         "--dump-json", "--no-download", "--no-playlist",
+        *_YT_CLIENT,
     ]
     runner = _meta_run if polite else _run
     stdout, stderr, code = runner([*base_cmd, *cookie_args], timeout=30)
@@ -379,6 +388,7 @@ def fetch_channel_metadata(channel_id: str, max_videos: int = 30, start_video: i
         "--dump-single-json",
         "--flat-playlist",
         "--quiet",
+        *_YT_CLIENT,
         *_cookie_args(),
     ]
     if start_video > 1:
@@ -442,6 +452,7 @@ def fetch_channel_playlists(channel_id: str, max_results: int = 100) -> list[dic
         "--dump-json", "--flat-playlist",
         "--playlist-end", str(max_results),
         "--quiet",
+        *_YT_CLIENT,
         *_cookie_args(),
     ], timeout=60)
 
@@ -484,6 +495,7 @@ def fetch_playlist_videos(playlist_id: str, max_videos: int = 200) -> list[dict]
         "yt-dlp", url,
         "--dump-json", "--flat-playlist",
         "--quiet",
+        *_YT_CLIENT,
         *_cookie_args(),
     ]
     if max_videos > 0:
@@ -532,6 +544,7 @@ def fetch_featured_channels(channel_id: str) -> list[str]:
         "--dump-json",
         "--flat-playlist",
         "--quiet",
+        *_YT_CLIENT,
         *_cookie_args(),
     ], timeout=30)
 
@@ -564,6 +577,7 @@ def fetch_channel_links(channel_id: str) -> list[str]:
         "--flat-playlist",
         "--playlist-end", "1",
         "--quiet",
+        *_YT_CLIENT,
         *_cookie_args(),
     ], timeout=30)
 
@@ -614,6 +628,7 @@ def download_subs_only(video_id: str, subtitle_langs: str) -> bool:
         "--sub-langs", subtitle_langs,
         "--convert-subs", "vtt",
         "-o", output_template,
+        *_YT_CLIENT,
         *_cookie_args(),
     ], timeout=60)
     if code == 0:
@@ -628,7 +643,7 @@ def fetch_available_subs(video_id: str) -> dict:
     BCP-47 lang codes. Manual = human-made; auto = auto-generated captions.
     """
     url = f"https://www.youtube.com/watch?v={video_id}"
-    base_cmd = ["yt-dlp", url, "--dump-json", "--no-download", "--no-playlist"]
+    base_cmd = ["yt-dlp", url, "--dump-json", "--no-download", "--no-playlist", *_YT_CLIENT]
     cookie_args = _cookie_args()
     stdout, _, code = _meta_run([*base_cmd, *cookie_args], timeout=30)
     if code != 0 and cookie_args:
@@ -674,6 +689,7 @@ def fetch_video_comments(youtube_video_id: str, max_comments: int = 20) -> list[
             "--skip-download",
             "--no-playlist",
             "--output", out_tmpl,
+            *_YT_CLIENT,
             *_cookie_args(),
         ]
         _run(args, timeout=90)
@@ -928,6 +944,7 @@ def start_download(
                     "-o", output_template,
                     "--newline", "--progress", "--no-colors",
                     *subtitle_args,
+                    *_YT_CLIENT,
                     *cookie_args,
                 ]
                 cmd, tmp_cookie_path = _make_private_cookie_copy(cmd)