fix(windows): transcode WebP cover to PNG for the media controls (#1102)

Windows SMTC could not render our cached WebP album covers: souvlaki loads the
file and SetThumbnail/set_metadata succeed, but the lock screen and Quick
Settings media tile showed a blank cover, because the OS thumbnail decoder does
not handle WebP even with the Store WebP extension installed.

Transcode local file:// WebP covers to PNG (libwebp decode then image PNG
encode, into a single reusable temp file) before handing them to the OS media
controls, gated to Windows. macOS (ImageIO) and Linux pass through unchanged.

CHANGELOG.md

@@ -43,6 +43,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 * On large libraries (reported with ~200,000 tracks on Navidrome), background library sync could lock up database writes for minutes at a time — playback history, ratings and other saves piled up waiting behind it.
 * Root cause: the track id-remap step ran a database lookup that couldn't use its indexes and scanned the entire track table once per incoming track, so the cost grew with the square of the library size. The lookup now uses the proper indexes, bringing it back to a fast, near-instant operation.
 
+### Album cover missing in Windows media controls
+
+* On Windows, the system media controls (the Quick Settings media tile, the lock screen and third-party media flyouts) showed the track title and artist but no album cover. Windows could not decode the cached WebP cover art for its thumbnail, even with the Store WebP extension installed. The cover is now converted to PNG before it is handed to the media controls, so the artwork shows again. macOS and Linux are unaffected.
+
 ### Windows media controls showed "Unknown application"
 
 * On Windows, the system media controls (the Quick Settings media tile, the lock screen and third-party media flyouts) labelled playback as "Unknown application" with no icon. The app now registers an explicit application identity at startup so Windows shows "Psysonic" and its icon as the playback source.

src-tauri/src/lib_commands/app_api/integration.rs

@@ -84,6 +84,15 @@ pub(crate) fn mpris_set_metadata(
     let duration = duration_secs.map(Duration::from_secs_f64);
     let mut guard = controls.lock().unwrap();
     let Some(ctrl) = guard.as_mut() else { return Ok(()); };
+
+    // #1102: Windows SMTC cannot render our cached WebP covers. souvlaki loads
+    // the file and SetThumbnail/set_metadata succeed, but the lock screen and
+    // Quick-Settings media tile show a blank cover (the OS thumbnail decoder
+    // does not handle WebP, even with the Store WebP extension installed).
+    // Transcode local WebP covers to PNG for the OS media controls; macOS
+    // (ImageIO) decodes WebP fine, so other platforms pass through unchanged.
+    let cover_url = smtc_cover_url(cover_url);
+
     ctrl.set_metadata(MediaMetadata {
         title: title.as_deref(),
         artist: artist.as_deref(),
@@ -94,6 +103,48 @@ pub(crate) fn mpris_set_metadata(
     .map_err(|e| format!("MPRIS set_metadata failed: {e:?}"))
 }
 
+/// Rewrite a cached WebP cover URL to a PNG the OS media controls can render.
+/// Windows SMTC cannot decode WebP thumbnails (#1102); other platforms and any
+/// non-`file://`/non-WebP URL pass through unchanged.
+fn smtc_cover_url(cover_url: Option<String>) -> Option<String> {
+    #[cfg(target_os = "windows")]
+    {
+        if let Some(url) = cover_url.as_deref() {
+            if let Some(path) = url.strip_prefix("file://") {
+                let is_webp = std::path::Path::new(path)
+                    .extension()
+                    .is_some_and(|e| e.eq_ignore_ascii_case("webp"));
+                if is_webp {
+                    match webp_file_to_temp_png(path) {
+                        Ok(png) => return Some(format!("file://{png}")),
+                        Err(e) => {
+                            crate::app_eprintln!("[mpris] cover WebP->PNG transcode failed: {e}")
+                        }
+                    }
+                }
+            }
+        }
+    }
+    cover_url
+}
+
+/// Decode a WebP file (libwebp, the same codec that wrote the cover cache) and
+/// re-encode it as a PNG in the temp dir, returning the native path. A single
+/// reusable file is fine: souvlaki reads it synchronously inside `set_metadata`,
+/// and the controls mutex serializes calls so it is never written concurrently.
+#[cfg(target_os = "windows")]
+fn webp_file_to_temp_png(webp_path: &str) -> Result<String, String> {
+    let bytes = std::fs::read(webp_path).map_err(|e| e.to_string())?;
+    let decoded = webp::Decoder::new(&bytes)
+        .decode()
+        .ok_or_else(|| "WebP decode returned None".to_string())?;
+    let img = decoded.to_image();
+    let out = std::env::temp_dir().join("psysonic-smtc-cover.png");
+    img.save_with_format(&out, image::ImageFormat::Png)
+        .map_err(|e| e.to_string())?;
+    Ok(out.to_string_lossy().into_owned())
+}
+
 #[tauri::command]
 pub(crate) fn mpris_set_playback(
     controls: tauri::State<MprisControls>,