Function without_server_chosen_subtitle 

pub fn without_server_chosen_subtitle(url: &str) -> String

Rewrite a stream URL so it asks for no subtitle, whoever built it.

playback_subtitle_stream_index only governs the URLs this app builds. When PlaybackInfo answers with a TranscodingUrl, the URL was built by the server from its own subtitle verdict, and we play it verbatim — so a server that picked a track anyway (a live channel opened without an index, a source whose default is image-based) hands us SubtitleMethod=Encode, and the burn-in the negotiation just declined comes back through the URL. Burn-in is a video cost: it rules out remuxing and forces a full re-encode.

Stripping the keys is not enough on its own — an absent index is not “none”, it is “you choose” — so the sentinel is always appended.

TRACES: UR-020, UR-004 | DR-176 | UT-168