# Requirements Specification

This document captures JellyTau's user requirements, software requirements,
traceability matrix, test traceability, and known technical debt.

For a narrative overview of the system design, see
[docs/architecture/](architecture/). For development workflows, see the
[README](../README.md) and [scripts/README.md](../scripts/README.md).

## 1. User Requirements

| ID | Requirement | Priority | Status |
|----|-------------|----------|--------|
| UR-001 | Run the app on multiple platforms (Linux, Android) | High | In Progress |
| UR-002 | Access media when online or offline | High | Done |
| UR-003 | Play videos | High | Done |
| UR-004 | Play audio uninterrupted | High | Done |
| UR-005 | Control media playback (pause, play, skip, scrub) | High | Done |
| UR-006 | Control media when device is on lock screen or via BLE headsets | Medium | Done |
| UR-007 | Navigate media in library | High | Done |
| UR-008 | Search media across libraries | High | Done |
| UR-009 | Connect to Jellyfin to access media | High | Done |
| UR-010 | Control playback of Jellyfin remote sessions | Low | Done |
| UR-011 | Download media on demand | Medium | Done |
| UR-012 | Login info shall be stored securely and persistently | High | Done |
| UR-013 | View and manage downloaded media | Medium | Done |
| UR-014 | Make and edit playlists of music that sync back to Jellyfin | Medium | Done |
| UR-015 | View and manage current audio queue (add, reorder tracks) | Medium | Done |
| UR-016 | Change system settings while playing (brightness, volume) | Low | Planned |
| UR-017 | Like or unlike audio, albums, movies, etc. | Medium | Done |
| UR-018 | Choose to download series, albums, songs, artist discography | Medium | Done |
| UR-019 | Resume playback from where you left off (movies, shows, albums) | High | Done |
| UR-020 | Select subtitles for video content | High | Done |
| UR-021 | Select audio track for video content | High | Done |
| UR-022 | Control streaming quality and transcoding settings | Medium | Planned |
| UR-023 | View "Next Up" / Continue Watching on home screen; auto-play next episode with countdown popup and configurable episode limit | Medium | Done |
| UR-024 | View recently added content on server | Medium | Done |
| UR-025 | Sync watch history and progress back to Jellyfin | High | Done |
| UR-026 | Sleep timer for audio and video playback (roller UI, time/track/episode modes) | Low | Done |
| UR-027 | Audio equalizer for sound customization | Low | Planned |
| UR-028 | Navigate to artist/album by tapping names in now playing view | High | Done |
| UR-029 | Toggle between grid and list view in library | Medium | Done |
| UR-030 | Quick genre browsing and filtering | Medium | Done |
| UR-031 | Crossfade between audio tracks | Low | Done (Linux only) |
| UR-032 | Gapless playback for seamless album listening | Medium | Done (Linux only) |
| UR-033 | Volume normalization to prevent volume jumps between tracks | Low | Done (Linux only) |
| UR-034 | Rich home screen with hero banners, carousels, and personalized sections | High | Done |
| UR-035 | View cast/crew (actors, directors) on movie/show detail pages | High | Done |
| UR-036 | Navigate to actor/person page showing their filmography | Medium | Done |
| UR-037 | Visually appealing video library with poster grids and metadata | High | Done |
| UR-038 | Movie/show detail page with backdrop, ratings, and rich metadata | High | Done |
| UR-039 | Navigate between main sections via bottom navigation bar | High | Done |

---

## 2. Software Requirements

### 2.1 Integration Requirements

External system integrations and platform-specific implementations.

| ID | Requirement | Category | Traces To | Status |
|----|-------------|----------|-----------|--------|
| IR-001 | Build system supporting multiple targets (Linux, Android) | Build | UR-001 | Done |
| IR-002 | Build scripts for Android and Linux | Build | UR-001 | Done |
| IR-003 | Integration of libmpv for Linux playback | Playback | UR-003, UR-004 | Done |
| IR-004 | Integration of ExoPlayer for Android playback | Playback | UR-003, UR-004 | In Progress (basic playback works, audio settings missing) |
| IR-005 | MPRIS D-Bus integration for Linux lockscreen/media controls | Platform | UR-006 | Planned |
| IR-006 | Android MediaSession integration for lockscreen controls | Platform | UR-006 | Done |
| IR-007 | Bluetooth AVRCP integration via system media session | Platform | UR-006 | Planned |
| IR-008 | Android audio focus handling (pause on call) | Platform | UR-004, UR-006 | Done |
| IR-009 | Jellyfin API client for authentication | API | UR-009, UR-012 | Done |
| IR-010 | Jellyfin API client for library browsing | API | UR-007, UR-008 | Done |
| IR-011 | Jellyfin API client for playback streaming | API | UR-003, UR-004 | Done |
| IR-012 | Jellyfin Sessions API for remote playback control | API | UR-010 | Done |
| IR-021 | Android MediaRouter integration for remote volume in system panel | Platform | UR-010, UR-016 | Planned |
| IR-013 | SQLite integration for local database | Storage | UR-002, UR-011 | Done |
| IR-014 | Secure credential storage (keyring/keychain) | Security | UR-012 | Done |
| IR-015 | Jellyfin API client for playback progress reporting | API | UR-019, UR-025 | Done |
| IR-016 | Jellyfin API client for subtitle/audio track info | API | UR-020, UR-021 | Done |
| IR-017 | Jellyfin API client for transcoding parameters | API | UR-022 | Planned |
| IR-018 | libmpv subtitle rendering and selection | Playback | UR-020 | Planned |
| IR-019 | libmpv audio track selection | Playback | UR-021 | Planned |
| IR-020 | libmpv/ExoPlayer equalizer integration | Playback | UR-027 | Planned |
| IR-022 | Jellyfin API client for person/cast data | API | UR-035, UR-036 | Done |
| IR-023 | Database schema for person/cast caching | Storage | UR-035, UR-036 | Done |
| IR-024 | Jellyfin API client for home screen data (featured, continue watching) | API | UR-034 | Done |

### 2.2 Jellyfin API Requirements

API endpoints and data contracts required for Jellyfin integration.

| ID | Requirement | Endpoint Category | Traces To | Status |
|----|-------------|-------------------|-----------|--------|
| JA-001 | Server connection and discovery | System | UR-009 | Done |
| JA-002 | User authentication (username/password) | Users | UR-009, UR-012 | Done |
| JA-003 | Get user library views | UserViews | UR-007 | Done |
| JA-004 | Get library items (paginated) | Items | UR-007 | Done |
| JA-005 | Get item details and metadata | Items | UR-007 | Done |
| JA-006 | Search across libraries | Items | UR-008 | Done |
| JA-007 | Get playback info and stream URL | MediaInfo | UR-003, UR-004 | Done |
| JA-008 | Get available subtitles for item | MediaInfo | UR-020 | Done |
| JA-009 | Get available audio tracks for item | MediaInfo | UR-021 | Done |
| JA-010 | Report playback start | Sessions | UR-025 | Done |
| JA-011 | Report playback progress (periodic) | Sessions | UR-025 | Done |
| JA-012 | Report playback stopped | Sessions | UR-025 | Done |
| JA-013 | Get resume position for item | UserData | UR-019 | Done |
| JA-014 | Get "Next Up" items | Shows | UR-023 | Done |
| JA-015 | Get "Continue Watching" items | Items | UR-023 | Done |
| JA-016 | Get recently added items | Items | UR-024 | Done |
| JA-017 | Mark item as favorite | UserData | UR-017 | Done |
| JA-018 | Remove item from favorites | UserData | UR-017 | Done |
| JA-019 | Get/create/update playlists | Playlists | UR-014 | Done |
| JA-020 | Add/remove items from playlist | Playlists | UR-014 | Done |
| JA-021 | Get active sessions list | Sessions | UR-010 | Done |
| JA-022 | Send playback commands to remote session (play/pause/stop) | Sessions | UR-010 | Done |
| JA-023 | Send seek command to remote session | Sessions | UR-010 | Done |
| JA-024 | Send next/previous track commands to remote session | Sessions | UR-010 | Done |
| JA-025 | Play specific item on remote session | Sessions | UR-010 | Done |
| JA-026 | Send volume/mute commands to remote session | Sessions | UR-010 | Done |
| JA-027 | Get transcoding options | MediaInfo | UR-022 | Planned |
| JA-028 | Get image/artwork URLs | Images | UR-007 | Done |
| JA-029 | Get cast/crew for item (actors, directors) | Items | UR-035 | Done |
| JA-030 | Get person details and filmography | Persons | UR-036 | Done |
| JA-031 | Get items by person (actor/director filmography) | Items | UR-036 | Done |

### 2.3 Development Requirements

Internal architecture, components, and application logic.

| ID | Requirement | Category | Traces To | Status |
|----|-------------|----------|-----------|--------|
| DR-001 | Player state machine (idle, loading, playing, paused, seeking, error) | Player | UR-005 | Done |
| DR-002 | MediaItem struct tracking source, location, duration, metadata | Player | UR-003, UR-004 | Done |
| DR-003 | Source-agnostic media abstraction (Remote, Local, DirectUrl) | Player | UR-002, UR-011 | Done |
| DR-004 | PlayerBackend trait for platform-agnostic playback | Player | UR-003, UR-004 | Done |
| DR-005 | Queue manager with shuffle, repeat, history | Player | UR-005, UR-015 | Done |
| DR-006 | Audio pre-caching for seamless track transitions | Player | UR-004 | Planned |
| DR-007 | Library browsing screens (grid view, search, filters) | UI | UR-007, UR-008 | Done |
| DR-008 | Album/Series detail view with track listing | UI | UR-007 | Done |
| DR-009 | Audio player UI (mini player, full screen) | UI | UR-005 | Done |
| DR-010 | Video player UI (fullscreen, controls overlay) | UI | UR-003, UR-005 | Done |
| DR-011 | Search bar with cross-library search | UI | UR-008 | Done |
| DR-012 | Local database for media metadata cache | Storage | UR-002 | Done |
| DR-013 | Repository pattern for online/offline data access | Storage | UR-002 | Done |
| DR-014 | Offline mutation queue for sync-back operations | Storage | UR-002, UR-014, UR-017 | Done |
| DR-015 | Download manager with queue and progress tracking | Storage | UR-011, UR-018 | Done |
| DR-016 | Thumbnail caching and sync with server | Storage | UR-007 | Done |
| DR-017 | "Manage Downloads" screen for local media management | UI | UR-013 | Done |
| DR-018 | Download buttons on library/album/player screens | UI | UR-011, UR-018 | Done |
| DR-019 | Playlist creation and editing UI | UI | UR-014 | Done |
| DR-020 | Queue management UI (add, remove, reorder) | UI | UR-015 | Done |
| DR-021 | Like/favorite functionality on media items | UI | UR-017 | Done |
| DR-022 | Resume position tracking and restoration on play | Player | UR-019 | Done |
| DR-023 | Subtitle selection UI in video player | UI | UR-020 | Done |
| DR-024 | Audio track selection UI in video player | UI | UR-021 | Done |
| DR-025 | Quality/transcoding settings UI | UI | UR-022 | Planned |
| DR-026 | "Continue Watching" / "Next Up" home section | UI | UR-023 | Done |
| DR-027 | "Recently Added" home section | UI | UR-024 | Done |
| DR-028 | Playback progress sync service (periodic reporting) | Player | UR-025 | Done |
| DR-029 | Sleep timer with roller UI, time/track/episode modes, and auto-stop (audio + video players) | Player | UR-026 | Done |
| DR-049 | Auto-play episode limit (configurable max episodes per session) | Player | UR-023 | Done |
| DR-050 | Reusable scroll picker (roller) component | UI | UR-026 | Done |
| DR-030 | Equalizer UI with presets and custom bands | UI | UR-027 | Planned |
| DR-031 | Clickable artist/album links in now playing view | UI | UR-028 | Done |
| DR-032 | List view option for library browsing (albums, artists) | UI | UR-029 | Done |
| DR-033 | Genre browsing screen with quick filters | UI | UR-030 | Done |
| DR-034 | Crossfade engine with configurable duration (0-12s) | Player | UR-031 | Done (Linux only) |
| DR-035 | Gapless playback between sequential tracks | Player | UR-032 | Done (Linux only) |
| DR-036 | Volume normalization with preset levels (Loud/Normal/Quiet) | Player | UR-033 | Done (Linux only) |
| DR-037 | Remote session browser and control UI | UI | UR-010 | Done |
| DR-038 | Home screen with hero banner carousel (featured/continue watching) | UI | UR-034 | Done |
| DR-039 | Home screen horizontal carousels (recently added, recommendations) | UI | UR-034, UR-024 | Done |
| DR-040 | Cast/crew section on movie/show detail pages | UI | UR-035 | Done |
| DR-041 | Person/actor detail page with filmography grid | UI | UR-036 | Done |
| DR-042 | Video library grid with poster cards, year, and rating badges | UI | UR-037 | Done |
| DR-043 | Movie/show detail page with backdrop hero, synopsis, and metadata | UI | UR-038 | Done |
| DR-044 | Horizontal scrolling actor/cast row with profile images | UI | UR-035 | Done |
| DR-045 | Bottom navigation bar with Home, Library, Search buttons | UI | UR-039 | Done |
| DR-046 | Dedicated search page with input and results | UI | UR-039 | Done |
| DR-047 | Next episode auto-play popup with configurable countdown and episode limit | Player | UR-023 | Done |
| DR-048 | Video settings (auto-play toggle, countdown duration, episode limit) | Settings | UR-023, UR-026 | Done |

---

## 3. Traceability Matrix

### User Requirements to Software Requirements

| User Req | Integration Requirements | Development Requirements |
|----------|-------------------------|-------------------------|
| UR-001 | IR-001, IR-002 | - |
| UR-002 | IR-013 | DR-003, DR-012, DR-013, DR-014 |
| UR-003 | IR-003, IR-004, IR-011 | DR-002, DR-004, DR-010 |
| UR-004 | IR-003, IR-004, IR-008, IR-011 | DR-002, DR-004, DR-006 |
| UR-005 | - | DR-001, DR-005, DR-009 |
| UR-006 | IR-005, IR-006, IR-007, IR-008 | - |
| UR-007 | IR-010 | DR-007, DR-008, DR-016 |
| UR-008 | IR-010 | DR-007, DR-011 |
| UR-009 | IR-009, IR-010, IR-011 | - |
| UR-010 | IR-012, IR-021 | DR-037 |
| UR-011 | IR-013 | DR-003, DR-015, DR-018 |
| UR-012 | IR-009, IR-014 | - |
| UR-013 | IR-013 | DR-017 |
| UR-014 | IR-010 | DR-014, DR-019 |
| UR-015 | - | DR-005, DR-020 |
| UR-016 | - | - |
| UR-017 | - | DR-014, DR-021 |
| UR-018 | IR-013 | DR-015, DR-018 |
| UR-019 | IR-015 | DR-022 |
| UR-020 | IR-016, IR-018 | DR-023 |
| UR-021 | IR-016, IR-019 | DR-024 |
| UR-022 | IR-017 | DR-025 |
| UR-023 | IR-010 | DR-026, DR-047, DR-048, DR-049 |
| UR-024 | IR-010 | DR-027 |
| UR-025 | IR-015 | DR-028 |
| UR-026 | - | DR-029, DR-048, DR-050 |
| UR-027 | IR-020 | DR-030 |
| UR-028 | - | DR-031 |
| UR-029 | - | DR-032 |
| UR-030 | IR-010 | DR-033 |
| UR-031 | - | DR-034 |
| UR-032 | - | DR-035 |
| UR-033 | - | DR-036 |
| UR-034 | IR-010, IR-024 | DR-038, DR-039 |
| UR-035 | IR-022, IR-023 | DR-040, DR-044 |
| UR-036 | IR-022, IR-023 | DR-041 |
| UR-037 | IR-010 | DR-042 |
| UR-038 | IR-010 | DR-043 |
| UR-039 | - | DR-045, DR-046 |

---

## 4. Test Traceability

### Unit Tests to Software Requirements

| Test ID | Test Description | Traces To | Status |
|---------|-----------------|-----------|--------|
| UT-001 | Player state transitions | DR-001 | Pending |
| UT-002 | MediaItem source URL resolution | DR-002, DR-003 | Pending |
| UT-003 | Queue next/previous navigation | DR-005 | Pending |
| UT-004 | Queue shuffle order generation | DR-005 | Pending |
| UT-005 | Queue repeat mode behavior | DR-005 | Pending |
| UT-006 | Jellyfin authentication flow | IR-009 | Pending |
| UT-007 | Jellyfin library items parsing | IR-010 | Pending |
| UT-008 | Repository pattern online/offline switching | DR-013 | Pending |
| UT-009 | Offline mutation queue persistence | DR-014 | Pending |
| UT-010 | Download queue management | DR-015 | Done |
| UT-011 | Resume position storage and retrieval | DR-022 | Pending |
| UT-012 | Sleep timer countdown logic | DR-029 | Pending |
| UT-013 | Playback progress reporting throttling | DR-028 | Pending |
| UT-014 | Database open and in-memory mode | IR-013, DR-012 | Done |
| UT-015 | Database migrations run successfully | IR-013, DR-012 | Done |
| UT-016 | All database tables created | IR-013, DR-012 | Done |
| UT-017 | FTS5 search table created | IR-013, DR-012 | Done |
| UT-018 | Server CRUD operations | IR-013, DR-012 | Done |
| UT-019 | User CRUD operations | IR-013, DR-012 | Done |
| UT-020 | Cascade delete server removes users | IR-013, DR-012 | Done |
| UT-021 | Item insert and FTS search | IR-013, DR-012 | Done |
| UT-022 | User data playback position storage | IR-013, DR-012, DR-022 | Done |
| UT-023 | Sync queue operations | IR-013, DR-014 | Done |
| UT-024 | Downloads table operations | IR-013, DR-015 | Done |
| UT-025 | Migrations are idempotent | IR-013, DR-012 | Done |
| UT-026 | NullBackend volume default value | DR-004 | Done |
| UT-027 | NullBackend set volume | DR-004 | Done |
| UT-028 | NullBackend volume clamping (high/low) | DR-004 | Done |
| UT-029 | NullBackend volume boundary values | DR-004 | Done |
| UT-030 | PlayerController volume default | DR-004, DR-009 | Done |
| UT-031 | PlayerController set volume | DR-004, DR-009 | Done |
| UT-032 | PlayerController muted default | DR-004, DR-009 | Done |
| UT-033 | PlayerController volume delegates to backend | DR-004, DR-009 | Done |
| UT-034 | Download event serialization roundtrip | DR-015 | Done |
| UT-035 | Download event completed serialization | DR-015 | Done |
| UT-036 | Download event failed serialization | DR-015 | Done |
| UT-037 | Download worker exponential backoff | DR-015 | Done |
| UT-038 | Download worker error retryable check | DR-015 | Done |
| UT-039 | Download manager creation | DR-015 | Done |
| UT-040 | Download manager set max concurrent | DR-015 | Done |
| UT-041 | Download info serialization | DR-015 | Done |
| UT-042 | Download command filename sanitization | DR-015, DR-018 | Done |
| UT-043 | Download command filename extension preservation | DR-015, DR-018 | Done |
| UT-044 | Offline item serialization | DR-017 | Done |
| UT-045 | Smart cache default config | DR-015 | Done |
| UT-046 | Smart cache album affinity tracking | DR-015 | Done |
| UT-047 | Smart cache queue precache config | DR-015 | Done |
| UT-048 | Smart cache storage limit check | DR-015 | Done |
| UT-049 | Playlist create (offline) | DR-019, JA-019 | Done |
| UT-050 | Playlist delete (offline) | DR-019, JA-019 | Done |
| UT-051 | Playlist rename (offline) | DR-019, JA-019 | Done |
| UT-052 | Playlist get items (offline) | DR-019, JA-019 | Done |
| UT-053 | Playlist add items (offline) | DR-019, JA-020 | Done |
| UT-054 | Playlist remove items (offline) | DR-019, JA-020 | Done |
| UT-055 | Playlist reorder items (offline) | DR-019, JA-020 | Done |
| UT-056 | Playlist entry serialization | DR-019, JA-019 | Done |
| UT-057 | Playlist Tauri command param naming (camelCase) | DR-019, JA-019, JA-020 | Done |
| UT-058 | Playlist repository client methods | DR-019, JA-019, JA-020 | Done |

### Integration Tests

| Test ID | Test Description | Traces To | Status |
|---------|-----------------|-----------|--------|
| IT-001 | End-to-end authentication with Jellyfin server | IR-009, UR-009 | Pending |
| IT-002 | Library browsing and item loading | IR-010, UR-007 | Pending |
| IT-003 | Audio playback via libmpv | IR-003, UR-004 | Pending |
| IT-004 | Video playback via libmpv | IR-003, UR-003 | Pending |
| IT-005 | MPRIS lockscreen controls on Linux | IR-005, UR-006 | Pending |
| IT-006 | Offline mode with local database | IR-013, UR-002 | Pending |
| IT-007 | Media download and local playback | DR-015, UR-011 | Pending |
| IT-008 | Subtitle track selection via libmpv | IR-018, UR-020 | Pending |
| IT-009 | Audio track selection via libmpv | IR-019, UR-021 | Pending |
| IT-010 | Playback progress sync to Jellyfin | IR-015, UR-025 | Pending |
| IT-011 | Resume playback from server position | IR-015, UR-019 | Pending |
| IT-012 | Equalizer bands via libmpv | IR-020, UR-027 | Pending |

---

## 5. Technical Debt

### Linux Keyring Integration Workaround

**Issue**: The `keyring-rs` crate (v3.x) has issues with retrieving credentials from the Linux Secret Service API, despite successfully saving them.

**Symptoms**:
- Credentials are saved to the system keyring successfully (verified with `secret-tool search`)
- Retrieval via the `keyring-rs` library fails with `NoEntry` error
- Session restoration fails on app restart even though credentials exist

**Root Cause**:
The `keyring-rs` library's Linux backend doesn't correctly retrieve entries from the Secret Service that it previously stored. This appears to be a bug in how the library interfaces with the Secret Service D-Bus API.

**Current Workaround**:
We bypass the `keyring-rs` library on Linux and use direct system calls to `secret-tool`:
- **Save**: `secret-tool store --label <label> service <service> username <username>`
- **Retrieve**: `secret-tool lookup service <service> username <username>`
- **Delete**: `secret-tool clear service <service> username <username>`

**Implementation**:
See [src-tauri/src/credentials.rs](../src-tauri/src/credentials.rs) for the
Linux-specific `secret-tool` save/get/delete paths.

**Future Fix**:
- Monitor `keyring-rs` for bug fixes in future versions
- Consider alternative secure storage libraries
- Test if newer versions of `keyring-rs` (v4.x+) resolve the issue
- Once fixed, remove the Linux-specific workaround and use the cross-platform `keyring-rs` API

**Impact**:
- Low - The workaround is functionally equivalent to proper keyring integration
- Credentials are stored securely in the system keyring
- Session restoration works correctly
- Only affects Linux; macOS and Windows use the standard `keyring-rs` implementation

**Dependencies**:
- Requires `secret-tool` to be installed on Linux systems (part of `libsecret-tools` package)
- Already available on most Linux distributions by default

---

### Platform Playback Backend Parity (Linux vs Android)

**Issue**: The Linux (MPV) and Android (ExoPlayer) playback backends have diverged in feature implementation and architecture patterns.

**Symptoms**:
- Audio settings (crossfade, gapless playback, volume normalization) work on Linux but not on Android
- Position update frequency differs between platforms (Linux: 250ms polling, Android: on-demand callbacks)
- Thread safety models differ (Linux: `Arc<Mutex<>>`, Android: global `OnceLock` statics)

**Root Cause**:
The `PlayerBackend` trait defines optional audio settings methods with default empty implementations. The Linux `MpvBackend` overrides these with full MPV property commands, but `ExoPlayerBackend` uses the defaults.

**Affected Files**:
- [src-tauri/src/player/backend.rs](../src-tauri/src/player/backend.rs) - Trait with default empty implementations
- [src-tauri/src/player/mpv_backend.rs](../src-tauri/src/player/mpv_backend.rs) - Full audio settings support
- [src-tauri/src/player/android/mod.rs](../src-tauri/src/player/android/mod.rs) - Missing audio settings implementation

**Feature Parity Matrix**:

| Feature | Linux (MPV) | Android (ExoPlayer) | Status |
|---------|-------------|---------------------|--------|
| Basic playback | ✅ | ✅ | Parity |
| Volume control | ✅ | ✅ | Parity |
| Seek | ✅ | ✅ | Parity |
| Crossfade | ✅ | ❌ | Gap |
| Gapless playback | ✅ | ❌ | Gap |
| Volume normalization | ✅ | ❌ | Gap |
| Position updates | 250ms | On-demand | Inconsistent |

**Future Fix**:
1. Implement `set_audio_settings()` in `ExoPlayerBackend`
2. Add Kotlin-side ExoPlayer configuration for crossfade (using `ConcatenatingMediaSource` or `DefaultMediaSourceFactory`)
3. Implement gapless via ExoPlayer's built-in gapless support
4. Add volume normalization via ExoPlayer's `LoudnessEnhancer` or audio processor
5. Standardize position update frequency across platforms

**Impact**:
- Medium - Android users lack audio enhancement features advertised in requirements
- User experience differs between platforms
- UR-031 (Crossfade), UR-032 (Gapless), UR-033 (Normalization) only work on Linux

**Traces To**: IR-004, UR-031, UR-032, UR-033, DR-034, DR-035, DR-036

---

### Frontend Playback Code Duplication

**Issue**: Playback control handlers and state derivations are duplicated between `AudioPlayer.svelte` and `MiniPlayer.svelte`.

**Symptoms**:
- Identical try-catch wrapped handler functions in both components (~44 lines duplicated)
- Same `$derived` state merging logic for local/remote playback in both components
- Position conversion (ticks ↔ seconds) scattered across multiple files

**Affected Files**:
- [src/lib/components/player/AudioPlayer.svelte](../src/lib/components/player/AudioPlayer.svelte) - Duplicate handlers
- [src/lib/components/player/MiniPlayer.svelte](../src/lib/components/player/MiniPlayer.svelte) - Duplicate handlers
- [src/lib/services/playbackControl.ts](../src/lib/services/playbackControl.ts) - Position conversion
- [src/lib/stores/playbackMode.ts](../src/lib/stores/playbackMode.ts) - Position conversion
- [src/lib/services/playbackReporting.ts](../src/lib/services/playbackReporting.ts) - Position conversion

**Duplicated Code**:
```typescript
// These handlers are identical in both AudioPlayer and MiniPlayer:
handlePlayPause(), handleNext(), handlePrevious(),
handleToggleShuffle(), handleCycleRepeat(), handleVolumeChange()

// These derived states use identical logic:
displayMedia, displayIsPlaying, displayPosition, displayDuration
```

**Future Fix**:
1. Create `src/lib/utils/playbackUnits.ts`:
   ```typescript
   export const TICKS_PER_SECOND = 10_000_000;
   export const secondsToTicks = (s: number) => Math.floor(s * TICKS_PER_SECOND);
   export const ticksToSeconds = (t: number) => t / TICKS_PER_SECOND;
   ```

2. Create `src/lib/composables/useMergedPlaybackState.svelte.ts`:
   - Export `displayMedia`, `displayIsPlaying`, `displayPosition`, `displayDuration`
   - Single source of truth for merged local/remote state

3. Simplify handler wrappers using a utility:
   ```typescript
   export const withErrorHandler = (fn: () => Promise<void>, context: string) =>
     async () => { try { await fn(); } catch (e) { console.error(`${context}:`, e); } };
   ```

**Impact**:
- Low - Code works correctly but violates DRY principle
- Maintenance burden when logic needs to change
- Risk of handlers diverging over time

**Traces To**: DR-009
