feat: support YouTube VTT subtitle selection

Checks/resolved-playback.py

@@ -70,7 +70,7 @@ class Handler(http.server.BaseHTTPRequestHandler):
         captions = path.startswith("/captions/")
         if alternate or captions:
             path = "/" + path.split("/", 2)[2]
-        expected = "alternate-private" if alternate else "subtitle-private" if captions or path == "/english.jpeg" else "stream-private"
+        expected = "alternate-private" if alternate else "subtitle-private" if captions or path in ("/english.jpeg", "/denied.vtt") else "stream-private"
         if self.headers.get("X-Resource") != expected:
             errors.append("wrong resource headers: " + path)
             self.send_error(403)
@@ -90,6 +90,11 @@ class Handler(http.server.BaseHTTPRequestHandler):
         elif path == "/english.jpeg":
             data = (b'WEBVTT\n\n00:00.000 --> 00:10.000\nAlternate English cue\n' if alternate else
                     b'WEBVTT\n\n00:00.000 --> 00:02.000\nFirst English cue\n\n00:02.000 --> 00:04.000\nSecond English cue\n')
+            if parse_qs(urlsplit(self.path).query).get("auto") == ["1"]:
+                data = data.replace(b"First English cue", b"First automatic cue").replace(b"Second English cue", b"Second automatic cue")
+        elif path == "/denied.vtt":
+            self.send_error(403)
+            return
         elif path.startswith("/resolved-vod-") and path.endswith(".ts"):
             data = (fixtures / path[1:]).read_bytes()
         else: