fix(playback): force a transcode when the webview cannot decode the audio (DR-149, 0.4.8)

Advertising a webview-shaped profile (DR-148) was necessary but not
sufficient. Probing the server directly showed Jellyfin 10.11.5 enforces a
DirectPlayProfile's Container and VideoCodec — excluding either returns
SupportsDirectPlay:false with TranscodeReasons=ContainerNotSupported /
VideoCodecNotSupported — but ignores its AudioCodec entirely: an E-AC-3
track is still offered for direct play against a profile listing only
aac,flac,mp3,opus,vorbis. Neither a VideoAudio CodecProfile forbidding the
codec nor MaxAudioChannels:2 against a 6-channel track changes the answer,
so no profile the client can send fixes this and the picture plays silent.

The client therefore stops delegating a question it can answer itself. The
negotiated source's audio is checked against what the webview decodes, and
an undecodable track forces the existing h264/aac HLS transcode regardless
of the server calling direct play fine; direct_play and needs_transcoding
are corrected to match so the frontend and the reporting path agree with
the URL actually used. The track judged is the one that would be served —
the default, else the first — since a supported track further down is not
the one that plays. A source with no audio, or a codec the server did not
name, is left alone rather than transcoded on a guess.

Test-first: the new tests failed against the old behaviour before the
decision existed. Verified on a motorola edge 30 by the audio HAL, not by
ear — the same E-AC-3 episode logged isMusicActive=true once and 58
ACDB-LOADER lines under this build, against 0 and 0 on 0.4.6, where an AAC
file in the same session produced 16 and 116. No FATAL EXCEPTION, so R8 on
the signed release build is unaffected.

Also carries in-flight subtitle-track work authored in a parallel session
(subtitleTracks, VideoPlayer, player/media, bindings) at the user's
request, so the tag matches the APK verified on device.

src-tauri/Cargo.lock

@@ -2018,7 +2018,7 @@ dependencies = [
 
 [[package]]
 name = "jellytau"
-version = "0.4.7"
+version = "0.4.8"
 dependencies = [
  "aes-gcm",
  "async-trait",

src-tauri/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "jellytau"
-version = "0.4.7"
+version = "0.4.8"
 description = "A Tauri App"
 authors = ["you"]
 edition = "2021"

src-tauri/src/repository/device_profile.rs

@@ -100,10 +100,99 @@ pub fn video_audio_codecs(detected: &str) -> String {
     }
 }
 
+/// Whether the webview `<video>` element can decode this audio codec.
+///
+/// TRACES: UR-004 | DR-149 | UT-143
+pub fn webview_can_decode_audio(codec: &str) -> bool {
+    WEBVIEW_AUDIO_CODECS
+        .iter()
+        .any(|supported| supported.eq_ignore_ascii_case(codec.trim()))
+}
+
+/// Decide whether we must transcode *regardless of what the server negotiated*,
+/// given the source's audio streams as `(codec, is_default)` in source order.
+///
+/// Advertising a narrow profile ([`video_audio_codecs`]) is necessary but not
+/// sufficient: Jellyfin 10.11.5 enforces a `DirectPlayProfile`'s container and
+/// video codec but **ignores its audio codec** — an E-AC-3 track is offered for
+/// direct play even when the profile lists only AAC, and neither a `VideoAudio`
+/// `CodecProfile` nor `MaxAudioChannels` changes that. So the client cannot
+/// delegate this decision; it knows what its own renderer can decode and must
+/// apply that itself.
+///
+/// The track that matters is the one the server will actually serve: the
+/// default, or the first when none is marked. An unknown codec is left alone —
+/// forcing a transcode on a guess would burn server CPU for files that play.
+///
+/// TRACES: UR-004 | DR-149 | UT-143
+pub fn audio_forces_transcode(streams: &[(Option<&str>, bool)]) -> bool {
+    let served = streams
+        .iter()
+        .find(|(_, is_default)| *is_default)
+        .or_else(|| streams.first());
+
+    match served {
+        Some((Some(codec), _)) => !webview_can_decode_audio(codec),
+        // No audio at all, or a codec the server did not name: leave it alone.
+        Some((None, _)) | None => false,
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
 
+    #[test]
+    fn an_undecodable_default_track_forces_a_transcode() {
+        // The reported bug: one E-AC-3 track, which the webview cannot decode.
+        assert!(audio_forces_transcode(&[(Some("eac3"), false)]));
+        assert!(audio_forces_transcode(&[(Some("ac3"), true)]));
+    }
+
+    #[test]
+    fn a_decodable_track_is_left_to_direct_play() {
+        // Never spend server CPU on a file that already plays.
+        assert!(!audio_forces_transcode(&[(Some("aac"), true)]));
+        assert!(!audio_forces_transcode(&[(Some("mp3"), false)]));
+    }
+
+    #[test]
+    fn the_default_track_decides_not_the_first() {
+        // The webview plays the default track, so that is the one that has to be
+        // decodable — a supported track further down does not save us.
+        assert!(audio_forces_transcode(&[
+            (Some("aac"), false),
+            (Some("eac3"), true)
+        ]));
+        assert!(!audio_forces_transcode(&[
+            (Some("eac3"), false),
+            (Some("aac"), true)
+        ]));
+    }
+
+    #[test]
+    fn with_no_default_marked_the_first_track_decides() {
+        // Jellyfin leaves IsDefault false on every stream for some files; the
+        // server then serves the first, so judge that one.
+        assert!(audio_forces_transcode(&[
+            (Some("eac3"), false),
+            (Some("aac"), false)
+        ]));
+    }
+
+    #[test]
+    fn a_source_with_no_audio_is_not_transcoded() {
+        // Nothing to rescue, and a transcode would not create audio.
+        assert!(!audio_forces_transcode(&[]));
+    }
+
+    #[test]
+    fn an_unknown_codec_is_not_second_guessed() {
+        // The server did not tell us the codec; assuming the worst would
+        // transcode files that play perfectly.
+        assert!(!audio_forces_transcode(&[(None, true)]));
+    }
+
     #[test]
     fn a_dolby_device_does_not_advertise_dolby_for_video() {
         // The bug: a Motorola reporting c2.dolby.eac3.decoder direct-played

src-tauri/src/repository/online.rs

@@ -1,9 +1,7 @@
 //! TRACES: UR-002, UR-007 | DR-013 | IR-010
 
 use async_trait::async_trait;
-#[cfg(target_os = "android")]
-use log::warn;
-use log::{debug, error, info};
+use log::{debug, error, info, warn};
 use serde::{Deserialize, Serialize};
 use std::sync::Arc;
 
@@ -1342,6 +1340,9 @@ impl MediaRepository for OnlineRepository {
             index: i32,
             #[serde(default)]
             codec: Option<String>,
+            /// The track the server serves when the client pins none.
+            #[serde(default)]
+            is_default: bool,
         }
 
         // Get detected codecs from Android MediaCodecList or use platform defaults
@@ -1475,9 +1476,29 @@ impl MediaRepository for OnlineRepository {
             );
         }
 
+        // Jellyfin 10.11.5 honours a DirectPlayProfile's container and video codec
+        // but ignores its audio codec, so it offers an E-AC-3 track for direct
+        // play even though DR-148 advertises only AAC — and the webview renders
+        // the picture in silence. Judge the track we would actually be served
+        // against what the webview can decode, and override the server's answer.
+        let audio_streams: Vec<(Option<&str>, bool)> = source
+            .media_streams
+            .iter()
+            .filter(|stream| stream.stream_type == "Audio")
+            .map(|stream| (stream.codec.as_deref(), stream.is_default))
+            .collect();
+        let audio_forces_transcode = super::device_profile::audio_forces_transcode(&audio_streams);
+
         // Use TranscodingUrl from response if available (Streamyfin pattern)
         let stream_url = if let Some(transcoding_url) = &source.transcoding_url {
             format!("{}{}", self.server_url, transcoding_url)
+        } else if audio_forces_transcode {
+            warn!(
+                "[PlaybackInfo] Server offered direct play for audio the webview cannot decode ({:?}) — forcing an HLS transcode",
+                audio_streams.first().and_then(|(codec, _)| *codec)
+            );
+            self.get_video_stream_url(item_id, Some(&source.id), None, None)
+                .await?
         } else {
             // Fall back to direct stream URL. No audioStreamIndex: static=true
             // serves the original file untouched, and pinning index 0 (the video
@@ -1498,8 +1519,9 @@ impl MediaRepository for OnlineRepository {
             media_source_id: source.id.clone(),
             play_session_id: response.play_session_id,
             stream_url,
-            direct_play: source.supports_direct_play,
-            needs_transcoding: !source.supports_direct_play && source.supports_transcoding,
+            direct_play: source.supports_direct_play && !audio_forces_transcode,
+            needs_transcoding: audio_forces_transcode
+                || (!source.supports_direct_play && source.supports_transcoding),
         })
     }
 

src-tauri/tauri.conf.json

@@ -1,7 +1,7 @@
 {
   "$schema": "https://schema.tauri.app/config/2",
   "productName": "jellytau",
-  "version": "0.4.7",
+  "version": "0.4.8",
   "identifier": "com.dtourolle.jellytau",
   "build": {
     "beforeDevCommand": "bun run dev",