ytdl_hook.lua: trim preceding text before JSON

There might be additional text in the output before the JSON payload if certain options like `--list-format` are specified in the config.

Author: TheDcoder

player/lua/ytdl_hook.lua

@@ -1006,6 +1006,16 @@ local function run_ytdl_hook(url)
     if result.status ~= 0 or json == "" then
         json = nil
     elseif json then
+        -- trim any preceding text before JSON
+        local start = string.find(json, "{", 1, true)
+        if start ~= 1 then
+            if start == nil then
+                msg.error("youtube-dl failed: couldn't find JSON data")
+                return
+            end
+            json = string.sub(json, start)
+        end
+
         json, parse_err = utils.parse_json(json)
     end