fix(player): strip the burn-in the server puts back into its own transcode URL

The negotiation asks for no subtitle stream (DR-176), but when PlaybackInfo answers with a TranscodingUrl we played that URL verbatim — and the server built it from its own subtitle verdict. Jellyfin's StreamInfo.ToUrl appends SubtitleStreamIndex and SubtitleMethod whenever it picked a track, so the burn-in we had just declined came straight back through the URL, turning a remux into a full frame-by-frame re-encode. Live TV never declined it at all: open_live_stream sent no index, so the server applied the channel's default track, and broadcast subtitles are DVB bitmaps that NormalizeSubtitleEmbed converts to burn-in on sight. without_server_chosen_subtitle() drops SubtitleStreamIndex, SubtitleMethod, SubtitleCodec and alwaysBurnInSubtitleWhenTranscoding from any URL the server built — matched case-insensitively, as Jellyfin binds query keys — and re-appends the -1 sentinel, because an absent index is not "none", it is "you choose". Applied at both adoption points, plus the sentinel in the live-stream negotiation body and its fallback URL.
2026-08-16 14:56:40 +02:00
parent d9e1e256e9
commit f0f98feae8
2 changed files with 151 additions and 3 deletions
@@ -122,6 +122,55 @@ pub fn playback_subtitle_stream_index() -> i32 {
    NO_SUBTITLE_STREAM
 }

+/// Query keys through which a stream URL can carry a subtitle decision.
+///
+/// Jellyfin binds query keys case-insensitively, so the match has to be too —
+/// the server itself mixes casing (`SubtitleStreamIndex` but
+/// `alwaysBurnInSubtitleWhenTranscoding`).
+const SUBTITLE_QUERY_KEYS: &[&str] = &[
+    "subtitlestreamindex",
+    "subtitlemethod",
+    "subtitlecodec",
+    "alwaysburninsubtitlewhentranscoding",
+];
+
+/// 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
+pub fn without_server_chosen_subtitle(url: &str) -> String {
+    let (path, query) = match url.split_once('?') {
+        Some((path, query)) => (path, query),
+        None => (url, ""),
+    };
+
+    let mut kept: Vec<&str> = query
+        .split('&')
+        .filter(|param| !param.is_empty())
+        .filter(|param| {
+            let key = param.split_once('=').map_or(*param, |(key, _)| key);
+            !SUBTITLE_QUERY_KEYS
+                .iter()
+                .any(|subtitle_key| key.eq_ignore_ascii_case(subtitle_key))
+        })
+        .collect();
+
+    let sentinel = format!("SubtitleStreamIndex={}", NO_SUBTITLE_STREAM);
+    kept.push(&sentinel);
+
+    format!("{}?{}", path, kept.join("&"))
+}
+
 /// Whether a subtitle in this format can reach the app as a sidecar it draws
 /// itself — the same verdict as [`subtitle_forces_burn_in`], from the reader's
 /// side, and the one a subtitle picker needs.
@@ -249,6 +298,81 @@ mod tests {
        assert_eq!(playback_subtitle_stream_index(), -1);
    }

+    /// A transcode URL the *server* built carries the server's own subtitle
+    /// verdict. Adopting it verbatim re-introduces the burn-in
+    /// [`playback_subtitle_stream_index`] exists to prevent — the negotiation
+    /// asks for no subtitle, and then we play a URL that asks for one anyway.
+    ///
+    /// TRACES: UR-020, UR-004 | DR-176 | UT-168
+    #[test]
+    fn a_server_built_transcode_url_has_its_burn_in_stripped() {
+        // Shape taken from Jellyfin's `StreamInfo.ToUrl`: it appends
+        // `SubtitleStreamIndex` and `SubtitleMethod` whenever it picked a track.
+        let served = "/videos/abc/master.m3u8?DeviceId=jt&MediaSourceId=src1\
+             &VideoCodec=h264&SubtitleMethod=Encode&SubtitleStreamIndex=2\
+             &PlaySessionId=xyz";
+
+        let url = without_server_chosen_subtitle(served);
+
+        assert!(
+            url.contains("SubtitleStreamIndex=-1"),
+            "the adopted URL must ask for no subtitle: {url}"
+        );
+        assert!(
+            !url.contains("SubtitleStreamIndex=2"),
+            "the server's chosen track must not survive: {url}"
+        );
+        assert!(
+            !url.contains("SubtitleMethod"),
+            "burn-in must not be requested: {url}"
+        );
+        // Everything else identifies the job and must survive untouched.
+        for kept in [
+            "DeviceId=jt",
+            "MediaSourceId=src1",
+            "VideoCodec=h264",
+            "PlaySessionId=xyz",
+        ] {
+            assert!(url.contains(kept), "{kept} must survive: {url}");
+        }
+    }
+
+    /// The server may also be told to burn in unconditionally
+    /// (`alwaysBurnInSubtitleWhenTranscoding`), which is appended to the URL
+    /// rather than expressed as a method — and its keys are not PascalCase.
+    ///
+    /// TRACES: UR-020, UR-004 | DR-176 | UT-168
+    #[test]
+    fn an_unconditional_burn_in_flag_is_stripped_whatever_its_casing() {
+        let url = without_server_chosen_subtitle(
+            "/videos/abc/master.m3u8?api_key=k&alwaysBurnInSubtitleWhenTranscoding=true\
+             &subtitlestreamindex=3&SubtitleCodec=ass",
+        );
+
+        assert!(!url.to_lowercase().contains("alwaysburnin"), "{url}");
+        assert!(!url.to_lowercase().contains("subtitlecodec"), "{url}");
+        assert!(!url.contains("subtitlestreamindex=3"), "{url}");
+        assert!(url.contains("SubtitleStreamIndex=-1"), "{url}");
+        assert!(url.contains("api_key=k"), "{url}");
+    }
+
+    /// A URL the server built without any subtitle in it still has to *say* so:
+    /// omitting the index is what makes the server apply the source's default.
+    ///
+    /// TRACES: UR-020, UR-004 | DR-176 | UT-168
+    #[test]
+    fn a_url_with_no_subtitle_params_is_still_made_to_ask_for_none() {
+        let url = without_server_chosen_subtitle("/videos/abc/master.m3u8?api_key=k");
+        assert_eq!(
+            url,
+            "/videos/abc/master.m3u8?api_key=k&SubtitleStreamIndex=-1"
+        );
+
+        // A bare URL is rare but must not come out malformed.
+        let bare = without_server_chosen_subtitle("/videos/abc/master.m3u8");
+        assert_eq!(bare, "/videos/abc/master.m3u8?SubtitleStreamIndex=-1");
+    }
+
    /// TRACES: UR-020 | DR-176 | UT-168
    #[test]
    fn text_subtitles_are_advertised_as_external_sidecars() {