ytdl_hook.lua: support playlist_title

Adds support for capturing the playlist_title from playlists and making
it available to subsequent instances of run_ytdl_hook()

This enables the inclusion of ytdl_playlist_title in the metadata
property for single videos which resulted from a playlist entry.

This may also be resolved with yt-dlp/yt-dlp#11234

player/lua/ytdl_hook.lua

@@ -28,6 +28,11 @@ end)
 local chapter_list = {}
 local playlist_cookies = {}
 
+local playlist = {
+    metadata = {},
+    path = {}
+}
+
 local function Set (t)
     local set = {}
     for _, v in pairs(t) do set[v] = true end
@@ -1079,6 +1084,12 @@ local function run_ytdl_hook(url)
             return
         end
 
+        -- capture the playlist metadata and associate it with all entries in
+        -- the playlist
+        playlist.metadata["playlist_title"] = json["title"]
+        playlist.metadata["playlist_id"] = json["id"]
+        playlist.path[json.original_url] = playlist.metadata
+
         local self_redirecting_url =
             json.entries[1]["_type"] ~= "url_transparent" and
             json.entries[1]["webpage_url"] and
@@ -1193,6 +1204,15 @@ local function run_ytdl_hook(url)
         end
 
     else -- probably a video
+        -- restore playlist metadata if any belong to the current url
+        local metadata = playlist.path[mp.get_property("playlist-path")] or {}
+
+        for key, value in pairs(metadata) do
+            if value then
+                json[key] = value
+            end
+        end
+
         add_single_video(json)
     end
     msg.debug('script running time: '..os.clock()-start_time..' seconds')