From 4daf1728344e762b514cd407cd19e56594f620a5 Mon Sep 17 00:00:00 2001
From: Duncan Tourolle <duncan@tourolle.paris>
Date: Thu, 24 Sep 2026 22:25:31 -0400
Subject: [PATCH] feat(windows): mpv plays audio on Windows, with libmpv
 shipped in the installer

libmpv on Windows (DR-237):
- The builder image carries zhongfly's LGPL libmpv-2.dll, pinned by
  asset name and sha256, plus an MSVC mpv.lib generated from the DLL's
  own mpv_* exports (the archive ships only a MinGW .dll.a). LGPL, not
  the GPL builds: no x264/x265, mpv -Dgpl=false; FFmpeg is version3, so
  LGPL-3.0. THIRD_PARTY_NOTICES.md records it.
- build-windows-cross.sh stages both files into src-tauri/windows-libs/;
  build.rs links mpv.lib from there and tauri.windows.conf.json bundles
  the DLL beside jellytau.exe from there, with the licence texts under
  licenses/. One directory, so the DLL shipped is the one linked.
- Workflows move to builder image 2026.09.1.

Windows audio:
- MpvBackend replaces WebviewAudioBackend on Windows (ao=wasapi), so
  volume, EQ, normalization and gapless work there as on Linux. Local
  files are passed to mpv as native paths, not file:// URLs.

Fixes found on the way:
- player_play_item decided "does the backend render video" with
  cfg!(not(linux)), true on Windows, while get_player_status sent
  Windows video to the <video> element. With mpv as the backend that
  would decode every film's soundtrack twice. All three callers now
  ask video_renders_natively() (UT-273).
- confine_queued_path rebuilt paths with PathBuf::push, so on Windows
  a queued `downloads/x` was stored as `downloads\x`, no longer the
  spelling the app built. It now keeps the caller's separator (UT-205,
  which only ever ran on Linux, failed under Windows).

Verified: jellytau.exe imports libmpv-2.dll; the full unit suite
cross-compiled for Windows passes under wine against the shipped DLL
(943/943, including the mpv injection and TLS tests); the NSIS
installer contains the DLL and licence texts. Not yet run on real
Windows hardware.
---
 .gitea/workflows/build-and-test.yml        |   6 +-
 .gitea/workflows/build-release.yml         |  10 +-
 .gitea/workflows/build-test-apk.yml        |   2 +-
 .gitea/workflows/publish-docs.yml          |   2 +-
 .gitea/workflows/traceability-check.yml    |   2 +-
 Dockerfile                                 |   4 +-
 Dockerfile.builder                         |  36 ++
 THIRD_PARTY_NOTICES.md                     |  21 +
 docs/build/build-windows.md                |  46 +-
 docs/requirements.md                       |   3 +-
 docs/specs/desktop-native-video.md         |   4 +-
 docs/specs/windows-native-audio-backend.md |  13 +-
 packaging/windows/GPL-3.0.txt              | 674 +++++++++++++++++++++
 packaging/windows/LGPL-3.0.txt             | 165 +++++
 scripts/build-windows-cross.sh             |  24 +-
 src-tauri/.gitignore                       |   4 +
 src-tauri/Cargo.toml                       |  10 +-
 src-tauri/build.rs                         |  29 +
 src-tauri/src/commands/download/mod.rs     |  35 +-
 src-tauri/src/commands/player/mod.rs       |  62 +-
 src-tauri/src/lib.rs                       |  29 +-
 src-tauri/src/player/mod.rs                |  15 +-
 src-tauri/src/player/mpv_backend.rs        |  25 +-
 src-tauri/tauri.windows.conf.json          |  12 +
 24 files changed, 1163 insertions(+), 70 deletions(-)
 create mode 100644 packaging/windows/GPL-3.0.txt
 create mode 100644 packaging/windows/LGPL-3.0.txt
 create mode 100644 src-tauri/tauri.windows.conf.json

diff --git a/.gitea/workflows/build-and-test.yml b/.gitea/workflows/build-and-test.yml
index c5356e7a8..11b0c9a90 100644
--- a/.gitea/workflows/build-and-test.yml
+++ b/.gitea/workflows/build-and-test.yml
@@ -28,7 +28,7 @@ jobs:
     if: "!startsWith(github.event.head_commit.message, 'chore(release)')"
     runs-on: linux/amd64
     container:
-      image: gitea.tourolle.paris/dtourolle/jellytau-builder:2026.08.1
+      image: gitea.tourolle.paris/dtourolle/jellytau-builder:2026.09.1
 
     steps:
       - name: Checkout repository
@@ -187,7 +187,7 @@ jobs:
     runs-on: linux/amd64
     needs: test
     container:
-      image: gitea.tourolle.paris/dtourolle/jellytau-builder:2026.08.1
+      image: gitea.tourolle.paris/dtourolle/jellytau-builder:2026.09.1
     env:
       ANDROID_HOME: /opt/android-sdk
       ANDROID_SDK_ROOT: /opt/android-sdk
@@ -256,7 +256,7 @@ jobs:
     name: Supply Chain
     runs-on: linux/amd64
     container:
-      image: gitea.tourolle.paris/dtourolle/jellytau-builder:2026.08.1
+      image: gitea.tourolle.paris/dtourolle/jellytau-builder:2026.09.1
 
     steps:
       - name: Checkout repository
diff --git a/.gitea/workflows/build-release.yml b/.gitea/workflows/build-release.yml
index c89fce65a..54d10e191 100644
--- a/.gitea/workflows/build-release.yml
+++ b/.gitea/workflows/build-release.yml
@@ -21,7 +21,7 @@ jobs:
     name: Run Tests
     runs-on: linux/amd64
     container:
-      image: gitea.tourolle.paris/dtourolle/jellytau-builder:2026.08.1
+      image: gitea.tourolle.paris/dtourolle/jellytau-builder:2026.09.1
     steps:
       - name: Checkout repository
         uses: actions/checkout@v4
@@ -94,7 +94,7 @@ jobs:
     runs-on: linux/amd64
     needs: test
     container:
-      image: gitea.tourolle.paris/dtourolle/jellytau-builder:2026.08.1
+      image: gitea.tourolle.paris/dtourolle/jellytau-builder:2026.09.1
     steps:
       - name: Checkout repository
         uses: actions/checkout@v4
@@ -235,7 +235,7 @@ jobs:
     # baked into the builder image. No toolchain installs here — the image has
     # cargo-xwin, clang/clang-cl, lld, llvm, nsis and the msvc target.
     container:
-      image: gitea.tourolle.paris/dtourolle/jellytau-builder:2026.08.1
+      image: gitea.tourolle.paris/dtourolle/jellytau-builder:2026.09.1
     steps:
       - name: Checkout repository
         uses: actions/checkout@v4
@@ -308,7 +308,7 @@ jobs:
     runs-on: linux/amd64
     needs: test
     container:
-      image: gitea.tourolle.paris/dtourolle/jellytau-builder:2026.08.1
+      image: gitea.tourolle.paris/dtourolle/jellytau-builder:2026.09.1
     env:
       ANDROID_HOME: /opt/android-sdk
       ANDROID_SDK_ROOT: /opt/android-sdk
@@ -411,7 +411,7 @@ jobs:
     needs: [build-linux, build-windows, build-android]
     if: startsWith(github.ref, 'refs/tags/v')
     container:
-      image: gitea.tourolle.paris/dtourolle/jellytau-builder:2026.08.1
+      image: gitea.tourolle.paris/dtourolle/jellytau-builder:2026.09.1
     steps:
       - name: Checkout repository
         uses: actions/checkout@v4
diff --git a/.gitea/workflows/build-test-apk.yml b/.gitea/workflows/build-test-apk.yml
index 49dfbb1ed..591c220a6 100644
--- a/.gitea/workflows/build-test-apk.yml
+++ b/.gitea/workflows/build-test-apk.yml
@@ -85,7 +85,7 @@ jobs:
         # The short-SHA output below avoids depending on it regardless.
         shell: bash
     container:
-      image: gitea.tourolle.paris/dtourolle/jellytau-builder:2026.08.1
+      image: gitea.tourolle.paris/dtourolle/jellytau-builder:2026.09.1
     env:
       ANDROID_HOME: /opt/android-sdk
       ANDROID_SDK_ROOT: /opt/android-sdk
diff --git a/.gitea/workflows/publish-docs.yml b/.gitea/workflows/publish-docs.yml
index 7d08d86b3..0603ee4db 100644
--- a/.gitea/workflows/publish-docs.yml
+++ b/.gitea/workflows/publish-docs.yml
@@ -21,7 +21,7 @@ jobs:
     name: Build & publish docs to gitea-pages
     runs-on: linux/amd64
     container:
-      image: gitea.tourolle.paris/dtourolle/jellytau-builder:2026.08.1
+      image: gitea.tourolle.paris/dtourolle/jellytau-builder:2026.09.1
 
     steps:
       - name: Checkout code
diff --git a/.gitea/workflows/traceability-check.yml b/.gitea/workflows/traceability-check.yml
index e8fd7fb58..403910b96 100644
--- a/.gitea/workflows/traceability-check.yml
+++ b/.gitea/workflows/traceability-check.yml
@@ -17,7 +17,7 @@ jobs:
     runs-on: linux/amd64
     name: Check Requirement Traces
     container:
-      image: gitea.tourolle.paris/dtourolle/jellytau-builder:2026.08.1
+      image: gitea.tourolle.paris/dtourolle/jellytau-builder:2026.09.1
 
     steps:
       - name: Checkout repository
diff --git a/Dockerfile b/Dockerfile
index 24bc944e8..ed5711c37 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -136,8 +136,8 @@ WORKDIR /app
 CMD ["bash", "-c", "OUTPUT_DIR=/app/dist scripts/build-desktop-linux.sh"]
 
 # Windows cross-compile environment (MSVC target via cargo-xwin). Video works via
-# WebView2 and audio via the webview <audio> backend; NSIS installer is produced
-# from Linux by cargo-xwin. Default bundles NSIS; override WIN_BUNDLES=none for
+# WebView2 and audio via mpv, whose DLL the builder image carries
+# (/opt/libmpv-win64); NSIS installer is produced from Linux by cargo-xwin. Default bundles NSIS; override WIN_BUNDLES=none for
 # exe-only. Build runs at container-run time like above.
 FROM ${BUILDER_IMAGE} AS windows-cross
 WORKDIR /app
diff --git a/Dockerfile.builder b/Dockerfile.builder
index a86e464d3..4d10e7f5f 100644
--- a/Dockerfile.builder
+++ b/Dockerfile.builder
@@ -186,6 +186,42 @@ RUN . $HOME/.cargo/env && \
     cargo cyclonedx --version && \
     mdbook --version
 
+# ---------------------------------------------------------------------------
+# libmpv for Windows (DR-237) — the Windows build links it and ships the DLL.
+#
+# zhongfly/mpv-winbuild's **LGPL** dev build: libmpv-2.dll with FFmpeg compiled
+# in, built `-Dgpl=false` with no x264/x265 and no --enable-gpl (its
+# compile-lgpl-libmpv.patch). FFmpeg keeps --enable-version3, so the DLL is
+# LGPL-3.0: the installer ships the licence texts and keeps the DLL a separate,
+# replaceable file — THIRD_PARTY_NOTICES.md. Not the default (GPL) asset from
+# the same release, and not shinchiro's, which is GPL-3.0 only.
+#
+# Pinned by asset name *and* sha256: GitHub prunes old releases from that repo,
+# so a rebuild after pruning fails loudly here rather than quietly taking a
+# newer build. To bump, change all three values.
+#
+# The archive ships a MinGW import library (libmpv.dll.a); the MSVC target needs
+# `mpv.lib`, generated from the DLL's own mpv_* exports so it cannot name a
+# symbol the DLL lacks. Output: $LIBMPV_WIN_DIR/{libmpv-2.dll,mpv.lib,include}.
+ENV LIBMPV_WIN_RELEASE=2026-09-24-2a4eb8067c \
+    LIBMPV_WIN_ASSET=mpv-dev-lgpl-x86_64-20260924-git-2a4eb8067c.7z \
+    LIBMPV_WIN_SHA256=f89c6195e13bfce3e8c0cc5d7f5d889ebdcf12184a41c8288360f5acd1e7306c \
+    LIBMPV_WIN_DIR=/opt/libmpv-win64
+RUN apt-get update && apt-get install -y --no-install-recommends libarchive-tools \
+    && rm -rf /var/lib/apt/lists/* \
+    && wget -q "https://github.com/zhongfly/mpv-winbuild/releases/download/${LIBMPV_WIN_RELEASE}/${LIBMPV_WIN_ASSET}" \
+        -O /tmp/mpv-dev.7z \
+    && echo "${LIBMPV_WIN_SHA256}  /tmp/mpv-dev.7z" | sha256sum -c - \
+    && mkdir -p "$LIBMPV_WIN_DIR" \
+    && bsdtar -xf /tmp/mpv-dev.7z -C "$LIBMPV_WIN_DIR" libmpv-2.dll include \
+    && rm /tmp/mpv-dev.7z \
+    && { echo "LIBRARY libmpv-2.dll"; echo "EXPORTS"; \
+         llvm-readobj --coff-exports "$LIBMPV_WIN_DIR/libmpv-2.dll" \
+           | awk '/Name: mpv_/ { print "    " $2 }'; } > "$LIBMPV_WIN_DIR/mpv.def" \
+    && llvm-lib /def:"$LIBMPV_WIN_DIR/mpv.def" /out:"$LIBMPV_WIN_DIR/mpv.lib" /machine:x64 \
+    && test "$(grep -c '^    mpv_' "$LIBMPV_WIN_DIR/mpv.def")" -ge 50 \
+    && ls -la "$LIBMPV_WIN_DIR"
+
 WORKDIR /app
 
 ENTRYPOINT ["/bin/bash"]
diff --git a/THIRD_PARTY_NOTICES.md b/THIRD_PARTY_NOTICES.md
index c0854ae4c..0660fdfaf 100644
--- a/THIRD_PARTY_NOTICES.md
+++ b/THIRD_PARTY_NOTICES.md
@@ -19,3 +19,24 @@ to the terms of the GPL-3.0**. The complete corresponding source for JellyTau is
 available in this repository; JellyTau's own code remains available under MIT.
 
 Desktop builds do not include this component.
+
+## Windows: libmpv (LGPL-3.0)
+
+The Windows installer bundles **`libmpv-2.dll`**, the mpv media player library
+with FFmpeg compiled in, which plays audio on Windows. It is the LGPL build from
+<https://github.com/zhongfly/mpv-winbuild> (mpv built `-Dgpl=false`, FFmpeg
+without `--enable-gpl`), pinned by version and checksum in `Dockerfile.builder`.
+
+- Licence: **GNU Lesser General Public License v3.0** (FFmpeg is configured
+  `--enable-version3`; mpv itself is LGPL-2.1-or-later in this configuration).
+  The installer carries the texts as `licenses/LGPL-3.0.txt` and
+  `licenses/GPL-3.0.txt`, which the LGPL-3.0 incorporates.
+- Source: mpv <https://github.com/mpv-player/mpv> and FFmpeg
+  <https://ffmpeg.org>, built by the scripts at
+  <https://github.com/zhongfly/mpv-winbuild>; the exact mpv commit is in the
+  asset name in `Dockerfile.builder`.
+
+JellyTau links it dynamically, and the DLL sits beside `jellytau.exe` as a
+separate file, so it can be replaced with any compatible libmpv build. JellyTau's
+own code remains under MIT. The Linux builds use the system's libmpv and do not
+bundle it.
diff --git a/docs/build/build-windows.md b/docs/build/build-windows.md
index ccd942900..e48a3c731 100644
--- a/docs/build/build-windows.md
+++ b/docs/build/build-windows.md
@@ -7,17 +7,31 @@ job / SMTC lockscreen), but it runs and plays media.
 
 ## How playback works on Windows
 
-- **Video** — renders through the webview HTML5 `<video>` element (hls.js) on
-  *every* platform; on Windows that is WebView2 (Chromium/Edge), which plays HLS +
-  h264 fine. No Windows-specific code.
-- **Audio-only (music)** — the native audio backends are libmpv (Linux) and
-  ExoPlayer (Android); neither exists on Windows. Instead
-  `create_player_backend()` in [../src-tauri/src/lib.rs](../../src-tauri/src/lib.rs)
-  uses `WebviewAudioBackend` on non-Linux/non-Android targets: it hands the stream
-  URL to a webview `<audio>` element (see
-  [../src/lib/services/webviewAudio.ts](../../src/lib/services/webviewAudio.ts)),
-  which reports state back through the same `player_report_*` round-trip the video
-  path uses. Pure Rust + Tauri events.
+- **Video** — renders through the webview HTML5 `<video>` element (hls.js); on
+  Windows that is WebView2 (Chromium/Edge), which plays HLS + h264 fine. mpv
+  takes this over in DR-237's video phase; Linux already made that move.
+- **Audio** — **libmpv**, the same `MpvBackend` Linux uses, with `ao=wasapi`.
+  Volume, EQ, normalization and gapless all go through mpv's filter graph as on
+  Linux. `libmpv-2.dll` ships beside `jellytau.exe` in the installer.
+
+### libmpv on Windows
+
+- **Which build:** zhongfly/mpv-winbuild's *LGPL* dev asset, pinned by name and
+  sha256 in [Dockerfile.builder](../../Dockerfile.builder), which unpacks it to
+  `/opt/libmpv-win64`. Licence terms: [THIRD_PARTY_NOTICES.md](../../THIRD_PARTY_NOTICES.md).
+  The same release also carries a GPL asset (x264/x265) — do not switch to it
+  casually, it moves the installer onto GPL-3.0 terms.
+- **Import library:** the archive only ships a MinGW `libmpv.dll.a`. The image
+  generates an MSVC `mpv.lib` from the DLL's own `mpv_*` exports
+  (`llvm-readobj --coff-exports` → `.def` → `llvm-lib /def:`), so it cannot name
+  a symbol the DLL lacks.
+- **One directory:** `scripts/build-windows-cross.sh` copies both files into
+  `src-tauri/windows-libs/` (gitignored) before building. `build.rs` links
+  `mpv.lib` from there and `tauri.windows.conf.json` bundles the DLL from there,
+  so the DLL shipped is the one linked against. Outside the image, point
+  `LIBMPV_WIN_DIR` at a directory holding `libmpv-2.dll` and `mpv.lib`.
+- **Bumping it:** change the three `LIBMPV_WIN_*` values together, rebuild and
+  push the image, bump the image tag the workflows pin.
 
 ## Cross-compiling from Linux (MSVC + cargo-xwin)
 
@@ -35,7 +49,7 @@ Tauri CLI bundle the **NSIS installer from a Linux host**.
 
 The builder image ([../Dockerfile.builder](../../Dockerfile.builder)) bakes in the
 whole toolchain: the `x86_64-pc-windows-msvc` rust target, `cargo-xwin`, `lld`,
-`llvm`, and `nsis`.
+`llvm`, `nsis`, and the pinned Windows libmpv.
 
 ```bash
 bun run docker:build:windows            # NSIS installer + .exe -> ./dist
@@ -71,8 +85,6 @@ Outputs:
 
 ## Outstanding for a first-class Windows release
 
-1. Gapless/crossfade + SMTC (lockscreen) — currently no-ops in the webview audio
-   path.
-2. Downloaded (`Local` source) file playback needs `convertFileSrc` on the
-   frontend; streaming works today.
-3. Code signing + a Windows packaging CI job.
+1. SMTC (lockscreen / media keys) — not wired on Windows.
+2. Code signing — the installer is unsigned.
+3. Video through mpv (DR-237) — needs a WebView2-side surface.
diff --git a/docs/requirements.md b/docs/requirements.md
index 4195b5637..042b48b59 100644
--- a/docs/requirements.md
+++ b/docs/requirements.md
@@ -439,7 +439,7 @@ Internal architecture, components, and application logic.
 | DR-234 | The device profile is derived from the **renderer that will decode the stream**, not from a compile-time platform constant. `video_codecs` was `#[cfg(target_os)]`, which is correct only while a build has one video renderer; once mpv and the webview element coexist it must be runtime state. This is the change that converts the measured 7% desktop direct-play rate toward the 85% the Android profile achieves on the same library, because the two differ by nothing except which component decodes. It looks like configuration and is not — it is the input that decides whether the server re-encodes, and getting it wrong fails silently, a claimed codec the renderer cannot decode being a black picture or silence (DR-148, and DR-227's audio override). The webview's narrower *audio* set stops applying to the video path once mpv decodes it, while the multichannel bound still does, since a 5.1 track direct-played into a two-channel sink is silence or inaudible dialogue | Repository | UR-080, UR-070 | In Progress |
 | DR-235 | The webview video path is deleted, not merely bypassed. Staged, because a path cannot be removed while a shipped platform still needs it: Linux moves to mpv first, Windows follows, and only then do `hls.js`, `html5Adapter.ts`, `videoLoaderFor` and the `<video>` element go. The staging is the point — a Linux-only version would leave the fork alive permanently, taking video from three renderers to four and giving every seek strategy, track switch and lifecycle bug one more place to be got right. Android keeps ExoPlayer and keeps the webview as its documented opt-out; the background-audio `<audio>` path is untouched. With no HTML5 fallback left, a failed mpv init emits `backend-init-failed` and surfaces a real error rather than silently degrading to the transcode this work exists to stop paying for | Playback | UR-080 | In Progress |
 | DR-236 | Hardware-decode policy is decided from what mpv reports it **selected** (`hwdec-current`), never from what it was asked for. The spike established that hardware decode works through the render API at all — the load-bearing result, since it means direct play is not bought with software decoding — but also that `auto` reached for the discrete GPU in copy-back mode on a hybrid Intel+NVIDIA laptop, the least efficient hardware path, and that `vaapi` fell back to software silently because the libva driver was absent. So zero-copy VA-API on the integrated GPU is preferred where the driver is present, `auto` is a fallback rather than the default, and a missing driver is detected and logged rather than mistaken for a compositing limit | Playback | UR-080 | Proposed |
-| DR-237 | Windows reaches the same mpv path, reusing everything except the surface. The surface is genuinely different code — a native child window beneath a transparent WebView2, not GTK — but the render context, lifetime discipline, frame pacing, device profile and hwdec policy are shared, which is why none of them may be guarded on `cfg!(target_os = "linux")`. The cost is mostly build, not video: `libmpv` is currently a Linux-only dependency while Windows is cross-compiled from Linux via `x86_64-pc-windows-msvc` + `cargo-xwin`, so a Windows libmpv must reach that cross-build and its DLL must ship in the NSIS bundle, carrying the LGPL obligations DR-216 already records — dynamic linkage, licence text shipped alongside. Windows gains a native audio decoder as a side effect, which is what the long-blocked Windows audio work wants and cannot otherwise have | Playback | UR-080 | Proposed |
+| DR-237 | Windows reaches the same mpv path, reusing everything except the surface. The surface is genuinely different code — a native child window beneath a transparent WebView2, not GTK — but the render context, lifetime discipline, frame pacing, device profile and hwdec policy are shared, which is why none of them may be guarded on `cfg!(target_os = "linux")`. The cost is mostly build, not video: `libmpv` is currently a Linux-only dependency while Windows is cross-compiled from Linux via `x86_64-pc-windows-msvc` + `cargo-xwin`, so a Windows libmpv must reach that cross-build and its DLL must ship in the NSIS bundle, carrying the LGPL obligations DR-216 already records — dynamic linkage, licence text shipped alongside. Windows gains a native audio decoder as a side effect, which is what the long-blocked Windows audio work wants and cannot otherwise have | Playback | UR-080 | In Progress |
 | DR-238 | A transcoded seek re-negotiates the stream on every renderer, not just the webview. Jellyfin produces a transcode *from* `StartTimeTicks`, so where a seek lands is a property of the request rather than of the stream in hand. `determine_video_seek_strategy` treated `is_hls` as a proxy for "seekable in place", which held only because hls.js was always the HLS renderer — it seeks within the VOD playlist it is handed and lets the server catch up. mpv's HLS demuxer cannot make the server transcode from a new offset, so with native video on, every transcoded seek became a backend seek that silently did nothing and presented as "resume does not work". The rule is now written on `needs_transcoding` with hls.js as the stated exception; all four webview cells are unchanged | Player | UR-040 | Done |
 | DR-239 | Properties the mpv event loop handles are registered with `observe_property`. libmpv delivers `PropertyChange` only for observed properties, so a `match` arm for an unobserved one is unreachable code that reads as implemented — the handler is right there. `pause` was handled and never observed, so `StateChanged` was never emitted on pause or resume and the play/pause control never moved. It stayed invisible while Linux video played in the webview, because the `<video>` element's own DOM events drove that control; native video made the UI depend on the event that never came | Player | UR-005 | Done |
 | DR-240 | Fullscreen moves whatever actually owns the pixels. `requestFullscreen()` fullscreens the *document*, which sufficed while every renderer lived inside it — the HTML5 `<video>` element is part of the document, so WebKit scaled it and the OS window's real size never mattered. A native surface is drawn behind the webview at **window** size, so a document-only fullscreen expands the page and leaves the picture where it was; on WebKitGTK the result is a maximised window with decorations still holding a strip of the screen, which reads as "fullscreen is broken" rather than as a windowing problem. Android needed the same rule for the system bars (DR-157); this is its desktop half | Player | UR-066 | Done |
@@ -868,6 +868,7 @@ Internal architecture, components, and application logic.
 | UT-270 | A hardened handle reads back `tls-verify=yes` and `ytdl=no`, and both mpv players harden the handle they create | DR-299 | Done |
 | UT-271 | Native video is on for Linux whatever `JELLYTAU_NATIVE_VIDEO` says, including unset and explicit "off" values, and off where mpv is not the video renderer | DR-235 | Done |
 | UT-272 | No platform reports a webview video fallback, Linux reports native video, and the player status on Linux never sends video to the `<video>` element | DR-235 | Done |
+| UT-273 | `player_play_item`, `get_player_status` and `player_get_capabilities` answer "does a native renderer draw video here" from one function, so the backend is loaded with video exactly where the frontend is told not to use a `<video>` element — on Windows, where mpv now plays audio, the film's soundtrack is not decoded twice | DR-237 | Done |
 ### Integration Tests
 
 | Test ID | Test Description | Traces To | Status |
diff --git a/docs/specs/desktop-native-video.md b/docs/specs/desktop-native-video.md
index cb0695a74..d6a3e58da 100644
--- a/docs/specs/desktop-native-video.md
+++ b/docs/specs/desktop-native-video.md
@@ -7,7 +7,9 @@ webview fallback is offered). **Left:** Linux's device profile still claims only
 the direct-play gain is not yet taken; `hwdec` is unset, so mpv decodes in
 software (DR-236); a failed surface attach only logs, it does not surface an
 error; the phase 1 soak and X11/Wayland criteria are unrecorded; phases 2 and 3.
-Phase 3 also deletes the now-inert frontend switch (`experimentalNativeVideo`,
+Phase 2 has started from its build half: Windows now links and ships libmpv
+(for audio, see windows-native-audio-backend.md); its video surface is not
+written. Phase 3 also deletes the now-inert frontend switch (`experimentalNativeVideo`,
 `nativeVideoWanted`, the Settings toggle and the adapter's suppressor flag),
 which no platform reaches since `webview_video_fallback` became false everywhere.
 **Requirements:** UR-080 (new) → DR-231 … DR-237 (new); IR-033 (new)
diff --git a/docs/specs/windows-native-audio-backend.md b/docs/specs/windows-native-audio-backend.md
index e45ce255f..56219a213 100644
--- a/docs/specs/windows-native-audio-backend.md
+++ b/docs/specs/windows-native-audio-backend.md
@@ -1,8 +1,15 @@
 # Spec: Windows native audio backend
 
-**Status:** Proposed — not started. Windows still runs on
-`WebviewAudioBackend`. Blocked on [libmpv2-migration.md](libmpv2-migration.md),
-whose crate swap has not landed either.
+**Status:** Partially implemented — code and packaging done, **unverified on
+Windows hardware**. `MpvBackend` is the Windows audio backend (`ao=wasapi`);
+the builder image carries zhongfly's pinned LGPL `libmpv-2.dll` plus a generated
+MSVC `mpv.lib`, and the NSIS installer ships the DLL beside `jellytau.exe` with
+its licence texts ([build-windows.md](../build/build-windows.md)). Done *before*
+the libmpv2 migration after all: the current `libmpv` pin cross-links fine, and
+the migration now has one call site to keep safe (`mpv_command`, DR-298) rather
+than a crate API to port twice. **Left:** every acceptance criterion that needs a
+Windows machine — audible volume/EQ/normalization/gapless, seek/queue/sleep
+timer, and the clean-VM install test.
 **Requirements:** UR-003, UR-027, UR-032, UR-033 → DR-030, DR-035, DR-036;
 ⚠️ the suggested id **IR-030 has since been allocated** to the scheduled catalog
 crawl — allocate a fresh id (IR-033 or later) on implementation
diff --git a/packaging/windows/GPL-3.0.txt b/packaging/windows/GPL-3.0.txt
new file mode 100644
index 000000000..f288702d2
--- /dev/null
+++ b/packaging/windows/GPL-3.0.txt
@@ -0,0 +1,674 @@
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+or that patent license was granted, prior to 28 March 2007.
+
+  Nothing in this License shall be construed as excluding or limiting
+any implied license or other defenses to infringement that may
+otherwise be available to you under applicable patent law.
+
+  12. No Surrender of Others' Freedom.
+
+  If conditions are imposed on you (whether by court order, agreement or
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+
+  13. Use with the GNU Affero General Public License.
+
+  Notwithstanding any other provision of this License, you have
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+  14. Revised Versions of this License.
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+  The Free Software Foundation may publish revised and/or new versions of
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+be similar in spirit to the present version, but may differ in detail to
+address new problems or concerns.
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+Program specifies that a certain numbered version of the GNU General
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+option of following the terms and conditions either of that numbered
+version or of any later version published by the Free Software
+Foundation.  If the Program does not specify a version number of the
+GNU General Public License, you may choose any version ever published
+by the Free Software Foundation.
+
+  If the Program specifies that a proxy can decide which future
+versions of the GNU General Public License can be used, that proxy's
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+to choose that version for the Program.
+
+  Later license versions may give you additional or different
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+  15. Disclaimer of Warranty.
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+  THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY
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+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
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+SUCH DAMAGES.
+
+  17. Interpretation of Sections 15 and 16.
+
+  If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+                     END OF TERMS AND CONDITIONS
+
+            How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+  If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+
+    <program>  Copyright (C) <year>  <name of author>
+    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+<https://www.gnu.org/licenses/>.
+
+  The GNU General Public License does not permit incorporating your program
+into proprietary programs.  If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.  But first, please read
+<https://www.gnu.org/licenses/why-not-lgpl.html>.
diff --git a/packaging/windows/LGPL-3.0.txt b/packaging/windows/LGPL-3.0.txt
new file mode 100644
index 000000000..0a041280b
--- /dev/null
+++ b/packaging/windows/LGPL-3.0.txt
@@ -0,0 +1,165 @@
+                   GNU LESSER GENERAL PUBLIC LICENSE
+                       Version 3, 29 June 2007
+
+ Copyright (C) 2007 Free Software Foundation, Inc. <https://fsf.org/>
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
+
+
+  This version of the GNU Lesser General Public License incorporates
+the terms and conditions of version 3 of the GNU General Public
+License, supplemented by the additional permissions listed below.
+
+  0. Additional Definitions.
+
+  As used herein, "this License" refers to version 3 of the GNU Lesser
+General Public License, and the "GNU GPL" refers to version 3 of the GNU
+General Public License.
+
+  "The Library" refers to a covered work governed by this License,
+other than an Application or a Combined Work as defined below.
+
+  An "Application" is any work that makes use of an interface provided
+by the Library, but which is not otherwise based on the Library.
+Defining a subclass of a class defined by the Library is deemed a mode
+of using an interface provided by the Library.
+
+  A "Combined Work" is a work produced by combining or linking an
+Application with the Library.  The particular version of the Library
+with which the Combined Work was made is also called the "Linked
+Version".
+
+  The "Minimal Corresponding Source" for a Combined Work means the
+Corresponding Source for the Combined Work, excluding any source code
+for portions of the Combined Work that, considered in isolation, are
+based on the Application, and not on the Linked Version.
+
+  The "Corresponding Application Code" for a Combined Work means the
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+Application, but excluding the System Libraries of the Combined Work.
+
+  1. Exception to Section 3 of the GNU GPL.
+
+  You may convey a covered work under sections 3 and 4 of this License
+without being bound by section 3 of the GNU GPL.
+
+  2. Conveying Modified Versions.
+
+  If you modify a copy of the Library, and, in your modifications, a
+facility refers to a function or data to be supplied by an Application
+that uses the facility (other than as an argument passed when the
+facility is invoked), then you may convey a copy of the modified
+version:
+
+   a) under this License, provided that you make a good faith effort to
+   ensure that, in the event an Application does not supply the
+   function or data, the facility still operates, and performs
+   whatever part of its purpose remains meaningful, or
+
+   b) under the GNU GPL, with none of the additional permissions of
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+
+  3. Object Code Incorporating Material from Library Header Files.
+
+  The object code form of an Application may incorporate material from
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+(ten or fewer lines in length), you do both of the following:
+
+   a) Give prominent notice with each copy of the object code that the
+   Library is used in it and that the Library and its use are
+   covered by this License.
+
+   b) Accompany the object code with a copy of the GNU GPL and this license
+   document.
+
+  4. Combined Works.
+
+  You may convey a Combined Work under terms of your choice that,
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+the following:
+
+   a) Give prominent notice with each copy of the Combined Work that
+   the Library is used in it and that the Library and its use are
+   covered by this License.
+
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+   document.
+
+   c) For a Combined Work that displays copyright notices during
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+   these notices, as well as a reference directing the user to the
+   copies of the GNU GPL and this license document.
+
+   d) Do one of the following:
+
+       0) Convey the Minimal Corresponding Source under the terms of this
+       License, and the Corresponding Application Code in a form
+       suitable for, and under terms that permit, the user to
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+   you use option 4d0, the Installation Information must accompany
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+   Information in the manner specified by section 6 of the GNU GPL
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+  5. Combined Libraries.
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+  You may place library facilities that are a work based on the
+Library side by side in a single library together with other library
+facilities that are not Applications and are not covered by this
+License, and convey such a combined library under terms of your
+choice, if you do both of the following:
+
+   a) Accompany the combined library with a copy of the same work based
+   on the Library, uncombined with any other library facilities,
+   conveyed under the terms of this License.
+
+   b) Give prominent notice with the combined library that part of it
+   is a work based on the Library, and explaining where to find the
+   accompanying uncombined form of the same work.
+
+  6. Revised Versions of the GNU Lesser General Public License.
+
+  The Free Software Foundation may publish revised and/or new versions
+of the GNU Lesser General Public License from time to time. Such new
+versions will be similar in spirit to the present version, but may
+differ in detail to address new problems or concerns.
+
+  Each version is given a distinguishing version number. If the
+Library as you received it specifies that a certain numbered version
+of the GNU Lesser General Public License "or any later version"
+applies to it, you have the option of following the terms and
+conditions either of that published version or of any later version
+published by the Free Software Foundation. If the Library as you
+received it does not specify a version number of the GNU Lesser
+General Public License, you may choose any version of the GNU Lesser
+General Public License ever published by the Free Software Foundation.
+
+  If the Library as you received it specifies that a proxy can decide
+whether future versions of the GNU Lesser General Public License shall
+apply, that proxy's public statement of acceptance of any version is
+permanent authorization for you to choose that version for the
+Library.
diff --git a/scripts/build-windows-cross.sh b/scripts/build-windows-cross.sh
index 308122814..bbe2fe80c 100755
--- a/scripts/build-windows-cross.sh
+++ b/scripts/build-windows-cross.sh
@@ -7,14 +7,16 @@
 # officially supports for Windows (the mingw/GNU target is not), and unlike GNU
 # it can bundle the NSIS installer from a Linux host.
 #
-# Playback on Windows: video renders via WebView2 and audio via the webview
-# <audio> backend (WebviewAudioBackend) — see docs/build/build-windows.md.
+# Playback on Windows: video renders via WebView2; audio via mpv, whose
+# libmpv-2.dll ships beside jellytau.exe — see docs/build/build-windows.md.
 #
 # Requirements (present in the Docker windows-cross target / unified builder):
 #   - rustup target x86_64-pc-windows-msvc
 #   - cargo-xwin           (cargo install --locked cargo-xwin)
 #   - lld, llvm            (linker + llvm-lib used by cargo-xwin)
 #   - nsis (makensis)      (installer generator)
+#   - libmpv for Windows   ($LIBMPV_WIN_DIR: libmpv-2.dll + mpv.lib, pinned and
+#                           sha256-checked in Dockerfile.builder)
 #
 # Usage:
 #   scripts/build-windows-cross.sh                    # exe + NSIS installer
@@ -29,10 +31,26 @@ WIN_BUNDLES="${WIN_BUNDLES:-nsis}"
 
 echo "🪟 Cross-compiling JellyTau for Windows ($TARGET, via cargo-xwin)"
 echo "================================================================"
-echo "Video plays via WebView2; audio via the webview <audio> backend."
+echo "Video plays via WebView2; audio via mpv (libmpv-2.dll)."
 echo "Bundles: $WIN_BUNDLES"
 echo ""
 
+# Stage libmpv where build.rs links it from and tauri.windows.conf.json bundles
+# it from — one directory, so the DLL shipped is the one linked against.
+# Copied fresh every build: a stale DLL left from an older image would ship
+# silently. TRACES: UR-004 | DR-237
+LIBMPV_WIN_DIR="${LIBMPV_WIN_DIR:-/opt/libmpv-win64}"
+for f in libmpv-2.dll mpv.lib; do
+  if [[ ! -f "$LIBMPV_WIN_DIR/$f" ]]; then
+    echo "❌ $LIBMPV_WIN_DIR/$f not found. Build inside the jellytau-builder image,"
+    echo "   or set LIBMPV_WIN_DIR to a directory holding libmpv-2.dll and mpv.lib."
+    exit 1
+  fi
+done
+rm -rf src-tauri/windows-libs
+mkdir -p src-tauri/windows-libs
+cp -v "$LIBMPV_WIN_DIR/libmpv-2.dll" "$LIBMPV_WIN_DIR/mpv.lib" src-tauri/windows-libs/
+
 bun install --frozen-lockfile 2>/dev/null || bun install
 bun run build
 
diff --git a/src-tauri/.gitignore b/src-tauri/.gitignore
index 63cd30b47..378185565 100644
--- a/src-tauri/.gitignore
+++ b/src-tauri/.gitignore
@@ -22,3 +22,7 @@ local.properties
 
 # macOS
 .DS_Store
+
+# Windows libmpv (import library + DLL), staged from the builder image by
+# scripts/build-windows-cross.sh. Never committed: 100 MB of LGPL binary.
+/windows-libs/
diff --git a/src-tauri/Cargo.toml b/src-tauri/Cargo.toml
index 3c1570d6b..1a26a5507 100644
--- a/src-tauri/Cargo.toml
+++ b/src-tauri/Cargo.toml
@@ -108,9 +108,10 @@ tiny_http = { version = "0.12.0", default-features = false }
 tauri-plugin-updater = "2"
 tauri-plugin-process = "2"
 
-# Linux-specific dependencies
-[target.'cfg(target_os = "linux")'.dependencies]
-hostname = "0.4"
+# mpv platforms: Linux (system libmpv) and Windows (libmpv-2.dll shipped in the
+# installer, import library generated in the builder image — see build.rs and
+# scripts/build-windows-cross.sh). TRACES: UR-004 | DR-237
+[target.'cfg(any(target_os = "linux", target_os = "windows"))'.dependencies]
 libc = "0.2"
 # The crates.io release of libmpv predates the MPV versions we support, so this
 # tracks the upstream git repo.
@@ -137,6 +138,9 @@ libmpv = { git = "https://github.com/ParadoxSpiral/libmpv-rs.git", rev = "3e6c38
 # TRACES: UR-080 | DR-230, IR-033
 libmpv-sys = { git = "https://github.com/ParadoxSpiral/libmpv-rs.git", rev = "3e6c389b716f52a595cc5e8e3fa1f96cb76b3de7" }
 
+# Linux-specific dependencies
+[target.'cfg(target_os = "linux")'.dependencies]
+hostname = "0.4"
 # Same major as the one Tauri/wry already resolve, so `gtk_window()` and
 # `default_vbox()` hand back types this crate can name rather than a second,
 # incompatible GTK.
diff --git a/src-tauri/build.rs b/src-tauri/build.rs
index d860e1e6a..3b842cf8a 100644
--- a/src-tauri/build.rs
+++ b/src-tauri/build.rs
@@ -1,3 +1,32 @@
+use std::path::PathBuf;
+
 fn main() {
+    link_windows_libmpv();
     tauri_build::build()
 }
+
+/// Point the MSVC linker at `mpv.lib` for a Windows target.
+///
+/// `libmpv-sys` emits `rustc-link-lib=mpv` and nothing else; on Linux the
+/// system library satisfies it. For Windows the import library and the DLL it
+/// names are staged into `src-tauri/windows-libs/` by
+/// `scripts/build-windows-cross.sh` from the builder image's pinned libmpv
+/// build — the same directory `tauri.windows.conf.json` bundles the DLL from,
+/// so what is linked against and what is shipped cannot come from two places.
+///
+/// TRACES: UR-004 | DR-237
+fn link_windows_libmpv() {
+    if std::env::var("CARGO_CFG_TARGET_OS").as_deref() != Ok("windows") {
+        return;
+    }
+    let dir = PathBuf::from(std::env::var("CARGO_MANIFEST_DIR").unwrap()).join("windows-libs");
+    println!("cargo:rerun-if-changed={}", dir.join("mpv.lib").display());
+    if !dir.join("mpv.lib").is_file() {
+        panic!(
+            "{} is missing. Windows builds link libmpv from the builder image; \
+             build through scripts/build-windows-cross.sh, which stages it.",
+            dir.join("mpv.lib").display()
+        );
+    }
+    println!("cargo:rustc-link-search=native={}", dir.display());
+}
diff --git a/src-tauri/src/commands/download/mod.rs b/src-tauri/src/commands/download/mod.rs
index 9708b264e..04721b15c 100644
--- a/src-tauri/src/commands/download/mod.rs
+++ b/src-tauri/src/commands/download/mod.rs
@@ -185,18 +185,45 @@ fn confine_to_root(root: &Path, candidate: &Path) -> Result<PathBuf, String> {
 ///
 /// TRACES: DR-211 | UT-205
 fn confine_queued_path(root: &Path, file_path: &str) -> Result<String, String> {
+    // The returned spelling keeps the caller's own separator. Rebuilding it with
+    // `PathBuf::push` rewrote `downloads/x` as `downloads\x` on Windows, so the
+    // stored row no longer spelled the path the app built — the contract the
+    // test below pins, which only ever ran on Linux.
+    // TRACES: DR-211 | UT-205
+    let sep = file_path
+        .chars()
+        .find(|c| std::path::is_separator(*c))
+        .unwrap_or('/');
     let mut sanitized = PathBuf::new();
+    let mut spelled = String::new();
+    let mut need_sep = false;
     for component in Path::new(file_path).components() {
-        match component {
-            Component::Normal(part) => sanitized.push(sanitize_filename(&part.to_string_lossy())),
+        let piece = match component {
+            Component::Normal(part) => sanitize_filename(&part.to_string_lossy()),
             // Kept as they are, so `confine_to_root` is the single thing
             // deciding whether what they add up to is still inside the root.
-            other => sanitized.push(other),
+            other => other.as_os_str().to_string_lossy().into_owned(),
+        };
+        sanitized.push(&piece);
+        match component {
+            Component::Prefix(_) => spelled.push_str(&piece),
+            Component::RootDir => {
+                spelled.push(sep);
+                need_sep = false;
+                continue;
+            }
+            _ => {
+                if need_sep {
+                    spelled.push(sep);
+                }
+                spelled.push_str(&piece);
+            }
         }
+        need_sep = !matches!(component, Component::Prefix(_));
     }
 
     confine_to_root(root, &root.join(&sanitized))?;
-    Ok(sanitized.to_string_lossy().to_string())
+    Ok(spelled)
 }
 
 /// Request payload for download_item_and_start (bundled to stay within specta's
diff --git a/src-tauri/src/commands/player/mod.rs b/src-tauri/src/commands/player/mod.rs
index a032db6ea..c7885b6f0 100644
--- a/src-tauri/src/commands/player/mod.rs
+++ b/src-tauri/src/commands/player/mod.rs
@@ -740,9 +740,11 @@ pub async fn player_play_item(
     //
     // This is the fifth place in this cycle where a renderer's capability was
     // written as a compile-time platform fact. Same fix as the others: ask.
+    // (It said `cfg!(not(linux))`, which also loaded Windows video into the
+    // backend while the status sent it to the `<video>` element.)
     //
-    // TRACES: UR-080 | DR-231, DR-235
-    let renders_natively = cfg!(not(target_os = "linux")) || crate::player::native_video::enabled();
+    // TRACES: UR-080 | DR-231, DR-235, DR-237
+    let renders_natively = video_renders_natively();
     if renders_natively {
         controller
             .play_item(media_item)
@@ -2203,14 +2205,18 @@ pub struct PlaybackCapabilities {
 #[tauri::command]
 #[specta::specta]
 pub async fn player_get_capabilities() -> Result<PlaybackCapabilities, String> {
-    // Mirrors the cfg gates the backends themselves are built under.
-    let native_audio = cfg!(any(target_os = "android", target_os = "linux"));
+    // Mirrors the cfg gates the backends themselves are built under: mpv on
+    // Linux and Windows (DR-237), ExoPlayer on Android.
+    let native_audio = cfg!(any(
+        target_os = "android",
+        target_os = "linux",
+        target_os = "windows"
+    ));
 
     Ok(PlaybackCapabilities {
         uses_webview_audio: !native_audio,
         // TRACES: UR-080 | DR-235
-        supports_native_video: cfg!(target_os = "android")
-            || crate::player::native_video::enabled(),
+        supports_native_video: video_renders_natively(),
         // No platform offers one: Android since DR-293, Linux since DR-235,
         // and on Windows the webview is the only video renderer, so there is
         // nothing to fall back *from*. Kept on the wire until phase 3 deletes
@@ -2220,12 +2226,25 @@ pub async fn player_get_capabilities() -> Result<PlaybackCapabilities, String> {
     })
 }
 
+/// Whether a native renderer draws video on this platform, so the backend
+/// must be handed the stream and the webview must not load it.
+///
+/// ExoPlayer on Android, mpv on Linux; the webview `<video>` element on
+/// Windows until DR-237 gives it mpv video. Asked by `player_play_item`,
+/// `get_player_status` and `player_get_capabilities` — the answer drifted when
+/// each spelled it out for itself.
+///
+/// TRACES: UR-003, UR-080 | DR-235, DR-237
+pub(crate) fn video_renders_natively() -> bool {
+    cfg!(target_os = "android") || crate::player::native_video::enabled()
+}
+
 pub(super) fn get_player_status(controller: &PlayerController) -> PlayerStatus {
     // Determine backend at compile time based on platform
     let (backend, use_html5_element) = if cfg!(target_os = "android") {
         // Android uses ExoPlayer native backend
         (VideoBackend::Native, false)
-    } else if crate::player::native_video::enabled() {
+    } else if video_renders_natively() {
         // mpv draws the picture on this desktop; the frontend must not also
         // load it into a <video> element or the stream decodes twice and the
         // two fight over the audio. TRACES: UR-080 | DR-235
@@ -3089,6 +3108,35 @@ mod tests {
         }
     }
 
+    /// The three places that answer "who draws video here" give one answer:
+    /// `play_item` loads the backend exactly where the status tells the
+    /// frontend *not* to use a `<video>` element. They disagreed on Windows —
+    /// `play_item` loaded video into the backend while the status sent it to
+    /// the element — which was invisible while that backend was the webview's
+    /// own `<audio>`, and would play every film's soundtrack twice once mpv
+    /// plays Windows audio.
+    ///
+    /// TRACES: UR-003, UR-080 | DR-235, DR-237 | UT-273
+    #[tokio::test]
+    async fn test_video_routing_has_one_answer() {
+        let src = include_str!("mod.rs");
+        let routing = src
+            .split("let renders_natively =")
+            .nth(1)
+            .and_then(|rest| rest.split(';').next())
+            .expect("player_play_item decides renders_natively");
+        assert_eq!(
+            routing.trim(),
+            "video_renders_natively()",
+            "player_play_item must ask the same question as get_player_status"
+        );
+
+        let status = super::get_player_status(&crate::player::PlayerController::default());
+        assert_eq!(status.use_html5_element, !super::video_renders_natively());
+        let caps = super::player_get_capabilities().await.unwrap();
+        assert_eq!(caps.supports_native_video, super::video_renders_natively());
+    }
+
     /// And the status the video page reads agrees: on Linux the frontend is told
     /// the native backend renders, never to load a `<video>` element.
     ///
diff --git a/src-tauri/src/lib.rs b/src-tauri/src/lib.rs
index 876afa692..7899b0a94 100644
--- a/src-tauri/src/lib.rs
+++ b/src-tauri/src/lib.rs
@@ -352,7 +352,7 @@ use player::{MediaSessionManager, PlayerBackend, PlayerController, TauriEventEmi
 // still launch (browse library, manage downloads, see an error) instead of crashing.
 use player::NullBackend;
 
-#[cfg(target_os = "linux")]
+#[cfg(any(target_os = "linux", target_os = "windows"))]
 use player::MpvBackend;
 use settings::VideoSettings;
 use storage::Database;
@@ -694,15 +694,26 @@ fn create_player_backend(
         }
     }
 
-    // For Linux, use MPV backend for audio playback
-    #[cfg(target_os = "linux")]
+    // Linux and Windows: mpv. On Windows libmpv-2.dll ships beside the exe in
+    // the installer (DR-237); on Linux it is the system library.
+    #[cfg(any(target_os = "linux", target_os = "windows"))]
     {
-        info!("Linux platform detected - initializing MPV backend for audio");
+        info!("Initializing MPV backend");
         match MpvBackend::new(Some(_event_emitter), playback_reporter, position_throttler) {
             Ok(backend) => {
-                info!("Successfully initialized MPV backend for Linux");
+                info!("Successfully initialized MPV backend");
                 Box::new(backend)
             }
+            #[cfg(target_os = "windows")]
+            Err(e) => {
+                // The DLL ships in the installer, so there is no package to
+                // tell the user to install; a failure here is a broken install.
+                error!("FATAL ERROR: Failed to initialize MPV backend: {}", e);
+                error!("libmpv-2.dll should sit beside jellytau.exe; reinstall JellyTau.");
+                emit_backend_init_failed(&app_handle, "mpv", e.to_string());
+                Box::new(NullBackend::new())
+            }
+            #[cfg(target_os = "linux")]
             Err(e) => {
                 error!("\n========================================");
                 error!("FATAL ERROR: Failed to initialize MPV backend");
@@ -731,10 +742,10 @@ fn create_player_backend(
         }
     }
 
-    // Platforms with no native audio backend (e.g. Windows): render audio-only
-    // playback through a webview <audio> element (all video already renders in
-    // the webview). Falls back to NullBackend only if the backend can't init.
-    #[cfg(not(any(target_os = "linux", target_os = "android")))]
+    // Platforms with no native audio backend (none that ships since Windows
+    // moved to mpv): render audio-only playback through a webview <audio>
+    // element. Falls back to NullBackend only if the backend can't init.
+    #[cfg(not(any(target_os = "linux", target_os = "android", target_os = "windows")))]
     {
         info!("No native audio backend for this platform - using webview <audio> backend");
         match player::WebviewAudioBackend::new(_event_emitter) {
diff --git a/src-tauri/src/player/mod.rs b/src-tauri/src/player/mod.rs
index 0c2337f17..08d448222 100644
--- a/src-tauri/src/player/mod.rs
+++ b/src-tauri/src/player/mod.rs
@@ -15,7 +15,7 @@ mod fake_player_conformance;
 pub mod legacy_player;
 pub mod media;
 pub mod media_player;
-#[cfg(target_os = "linux")]
+#[cfg(any(target_os = "linux", target_os = "windows"))]
 pub mod mpv_command;
 #[cfg(target_os = "linux")]
 pub mod mpv_player;
@@ -42,7 +42,7 @@ pub mod jni_guard;
 #[cfg(target_os = "android")]
 pub mod android;
 
-#[cfg(target_os = "linux")]
+#[cfg(any(target_os = "linux", target_os = "windows"))]
 pub mod mpv_backend;
 
 /// Whether this process renders video natively — one answer, three consumers
@@ -64,9 +64,10 @@ pub mod mpv_render;
 #[cfg(target_os = "linux")]
 pub mod video_surface;
 
-// Platforms with no native audio backend (e.g. Windows) render audio-only
-// playback through a webview <audio> element, mirroring how all video renders.
-#[cfg(not(any(target_os = "linux", target_os = "android")))]
+// Platforms with no native audio backend render audio-only playback through a
+// webview <audio> element. None that ships: Windows moved to mpv (DR-237); this
+// remains for an unported desktop (macOS).
+#[cfg(not(any(target_os = "linux", target_os = "android", target_os = "windows")))]
 pub mod webview_audio_backend;
 
 // Re-export commonly used types
@@ -88,10 +89,10 @@ pub use track_switch::{determine_audio_track_switch_strategy, AudioTrackSwitchSt
 #[cfg(target_os = "android")]
 pub use android::ExoPlayerBackend;
 
-#[cfg(target_os = "linux")]
+#[cfg(any(target_os = "linux", target_os = "windows"))]
 pub use mpv_backend::MpvBackend;
 
-#[cfg(not(any(target_os = "linux", target_os = "android")))]
+#[cfg(not(any(target_os = "linux", target_os = "android", target_os = "windows")))]
 pub use webview_audio_backend::WebviewAudioBackend;
 
 #[cfg(target_os = "android")]
diff --git a/src-tauri/src/player/mpv_backend.rs b/src-tauri/src/player/mpv_backend.rs
index a5c759248..4db51b73a 100644
--- a/src-tauri/src/player/mpv_backend.rs
+++ b/src-tauri/src/player/mpv_backend.rs
@@ -9,7 +9,6 @@ use crate::utils::conversions::{seconds_to_ticks, volume_to_percent};
 use crate::utils::lock::MutexSafe;
 use libmpv::Mpv;
 use log::{debug, error, info, warn};
-use std::process::Command;
 use std::sync::atomic::{AtomicU64, Ordering};
 use std::sync::{Arc, Mutex};
 use std::time::{Duration, SystemTime, UNIX_EPOCH};
@@ -54,8 +53,21 @@ struct InternalState {
     volume: f32,
 }
 
-/// Detect which audio system is available on the system
+/// The audio output mpv should use on Windows: WASAPI, the only one it ships
+/// there. Nothing to probe — and spawning `pactl` from a GUI app on Windows
+/// would at best fail and at worst flash a console window.
+///
+/// TRACES: UR-004 | DR-237
+#[cfg(target_os = "windows")]
 fn detect_audio_system() -> String {
+    "wasapi".to_string()
+}
+
+/// Detect which audio system is available on the system
+#[cfg(not(target_os = "windows"))]
+fn detect_audio_system() -> String {
+    use std::process::Command;
+
     info!("[MpvBackend] Detecting audio system...");
 
     // Try PulseAudio/PipeWire first (most common on modern Linux)
@@ -95,6 +107,13 @@ fn detect_audio_system() -> String {
 fn get_stream_url(media: &MediaItem) -> String {
     match &media.source {
         MediaSource::Remote { stream_url, .. } => stream_url.clone(),
+        // A Windows path is not a URL (`file://C:\...` is malformed); mpv
+        // takes the native path as it is. Safe to pass verbatim because it goes
+        // to mpv as one argv element (DR-298), not through a command string.
+        // TRACES: UR-004, UR-071 | DR-237
+        MediaSource::Local { file_path, .. } if cfg!(target_os = "windows") => {
+            file_path.to_string_lossy().into_owned()
+        }
         MediaSource::Local { file_path, .. } => {
             format!("file://{}", file_path.to_string_lossy())
         }
@@ -121,6 +140,8 @@ static MPV_HANDLE: std::sync::OnceLock<usize> = std::sync::OnceLock::new();
 /// can fail, and the app falls back to a no-op backend rather than dying).
 ///
 /// TRACES: UR-080 | DR-231
+// Only the Linux video surface reads it until Windows gets one (DR-237).
+#[cfg_attr(not(target_os = "linux"), allow(dead_code))]
 pub fn registered_handle() -> *mut libmpv_sys::mpv_handle {
     MPV_HANDLE
         .get()
diff --git a/src-tauri/tauri.windows.conf.json b/src-tauri/tauri.windows.conf.json
new file mode 100644
index 000000000..09659e283
--- /dev/null
+++ b/src-tauri/tauri.windows.conf.json
@@ -0,0 +1,12 @@
+{
+  "$schema": "https://schema.tauri.app/config/2",
+  "bundle": {
+    "resources": {
+      "windows-libs/libmpv-2.dll": "libmpv-2.dll",
+      "../THIRD_PARTY_NOTICES.md": "licenses/THIRD_PARTY_NOTICES.md",
+      "../packaging/windows/LGPL-3.0.txt": "licenses/LGPL-3.0.txt",
+      "../packaging/windows/GPL-3.0.txt": "licenses/GPL-3.0.txt",
+      "../LICENSE": "licenses/LICENSE-JellyTau-MIT.txt"
+    }
+  }
+}