pluriwave/openspec/specs/android-auto-media/spec.md

Android Auto Media Specification

Purpose

PluriWave MUST expose a browsable station tree and play-by-media-id interface to Android Auto (projected) via the existing PluriWaveAudioHandler (audio_service MediaBrowserService/MediaSession), so a driver can browse and play stations from the car head unit without rebuilding the audio pipeline.

Requirements

Requirement: Android Auto Discovery Declaration

The app MUST declare itself as a media app to Android Auto so the car head unit discovers it.

Scenario: Android Auto scans installed apps

• GIVEN PluriWave is installed on the phone
• WHEN Android Auto scans installed apps for car-app support
• THEN it finds res/xml/automotive_app_desc.xml declaring <uses name="media"/>
• AND the AndroidManifest.xml <application> block declares <meta-data android:name="com.google.android.gms.car.application" android:resource="@xml/automotive_app_desc"/>
• AND PluriWave appears in the car's media app list

Requirement: Favorite Group Sub-Folders

The Android Auto browse tree MUST expose favorite groups (GrupoFavoritos, as already modeled by Emisora.grupoFavoritosId and surfaced by EstadoRadio.gruposFavoritos) as browsable, non-playable sub-folders reachable from the existing Favoritos folder, without altering the 3 root folders (Favoritos, Todas las emisoras, Mis emisoras).

Scenario: Car requests the Favoritos folder and groups exist

• GIVEN the user has one or more favorite groups with at least one member station each
• WHEN getChildren is called with the Favoritos folder id
• THEN it returns one non-playable folder MediaItem per surfaced group, in addition to (or instead of, per the design's structural decision) any ungrouped favorite stations
• AND each group folder's id follows a browsable grupo:<id> scheme distinct from the emisora:<uuid> playable-item scheme

Scenario: Car requests a group folder's stations

• GIVEN a favorite group folder with id grupo:<id> was returned under Favoritos
• WHEN getChildren is called with that grupo:<id> folder id
• THEN it returns the playable MediaItems for exactly the stations whose Emisora.grupoFavoritosId matches <id>
• AND those items are sorted and capped using the same ordering and item-count rules already applied to the other folders (ordenarEmisoras, 50-item cap)
• AND selecting one of those items plays the corresponding station via the existing emisora:<uuid> playback path, unchanged

Scenario: Car requests an unknown or stale group id

• GIVEN a grupo:<id> id that does not match any group known to the current snapshot
• WHEN getChildren is called with that id
• THEN it returns an empty list, not an error

Requirement: Empty Favorite Group Handling

The system MUST produce a browsable tree that never presents a user-selectable folder promising content it cannot deliver: for any favorite group with zero member stations, the tree MUST either omit that group's folder from Favoritos's children, or include it and return an empty (not erroring) child list when browsed. The specific choice between omitting empty-group folders and showing-but-empty, and any related folder-count/flat-vs-nested structural decision for Favoritos, is deferred to sdd-design; whichever mechanism design selects MUST satisfy both scenarios below.

Scenario: Empty group folder is browsed (if shown)

• GIVEN a favorite group has zero member stations and the design's chosen mechanism surfaces it as a folder under Favoritos
• WHEN getChildren is called with that group's grupo:<id>
• THEN it returns an empty list, not an error

Scenario: No user-facing dead end

• GIVEN the full set of favorite groups, including any empty ones
• WHEN the Favoritos folder is browsed and then each of its returned children is browsed
• THEN no returned folder child ever throws, hangs, or surfaces a driver-facing error state
• AND the car head unit's total folder/item count presented under Favoritos remains within the driver-distraction-safe bounds design establishes

Requirement: Browsable Media Tree

getChildren MUST return a browsable tree rooted at AudioService.browsableRootId, organized into non-playable folders (Favoritos, Todas las emisoras, Mis emisoras, Ecualizador, and the local-music root) containing playable items. Playable station items SHOULD carry an audio-quality subtitle when known. The Favoritos folder additionally MAY contain non-playable favorite-group sub-folders (see "Favorite Group Sub-Folders"); Todas las emisoras and Mis emisoras remain flat. The Ecualizador folder is flat, non-playable, and contains only the 6 fixed EQ preset items (see "EQ Preset Browsable Folder"). The local-music root folder is non-playable and may itself be nested (see "Local Music Browsable Tree"). (Previously: root contained exactly 3 folders — Favoritos, Todas las emisoras, Mis emisoras — with no EQ or local-music folder; Favoritos was a flat folder of playable station items only, with no sub-folder nesting.)

Scenario: Car requests the root

• GIVEN the car head unit connects and requests the root (AudioService.browsableRootId)
• WHEN getChildren is called with the root id
• THEN it returns five folder MediaItems (Favoritos, Todas las emisoras, Mis emisoras, Ecualizador, and the local-music root), each with playable: false

Scenario: Car requests a folder with no stations

• GIVEN the user has zero favorite stations
• WHEN getChildren is called with the Favoritos folder id
• THEN it returns an empty list, not an error

Scenario: Browse requested before app state is loaded

• GIVEN the audio handler starts cold and station/favorites Provider state has not finished loading
• WHEN getChildren is called (root or any folder)
• THEN it returns a valid, possibly empty, list without throwing and without blocking or crashing the service

Scenario: Station has known codec and bitrate

• GIVEN a station's Emisora.codec and Emisora.bitrate are both known (non-null)
• WHEN it is mapped to a playable MediaItem
• THEN displaySubtitle SHALL contain a human-readable quality hint combining bitrate and codec (e.g. "128 kbps · MP3")

Scenario: Station has unknown codec or bitrate

• GIVEN a station's Emisora.codec or Emisora.bitrate (or both) is null/unknown
• WHEN it is mapped to a playable MediaItem
• THEN displaySubtitle SHALL omit the quality hint gracefully (no subtitle, or a subtitle with no quality fragment)
• AND the subtitle MUST NOT render literal placeholder text such as "null kbps" or "null · null"

Scenario: Ungrouped station appears exactly as before (regression guard)

• GIVEN a station's Emisora.grupoFavoritosId equals GrupoFavoritos.sinAsignarId ('sin_asignar', the default when no group is assigned)
• WHEN the Favoritos, Todas las emisoras, or Mis emisoras folders are browsed
• THEN that station appears as a playable emisora:<uuid> item in exactly the same folder(s), position (subject to existing sort rules), title, art, and subtitle as it did before favorite-group folders were introduced
• AND its presence and shape are unaffected by the existence, emptiness, or content of any favorite group

Requirement: EQ Preset Browsable Folder

The Android Auto browse tree MUST expose the 6 fixed EQ presets (PresetEcualizador.presets) as playable items inside the Ecualizador root folder, each using a distinct eq_preset:<nombre> media-id scheme, separate from emisora:<uuid> and grupo:<id>.

Scenario: Car requests the Ecualizador folder

• GIVEN the Ecualizador folder id was returned under the root
• WHEN getChildren is called with the Ecualizador folder id
• THEN it returns exactly 6 playable MediaItems, one per PresetEcualizador.presets entry, titled with the preset's name
• AND each item's id is eq_preset:<nombre>, where <nombre> is that preset's unique name

Requirement: EQ Preset Selection Applies Without Disturbing Playback

Selecting an eq_preset:<nombre> item MUST apply that preset immediately through the headless-safe EQ seam (e.g. PluriWaveAudioHandler.aplicarPreset), via a branch in playFromMediaId intercepted BEFORE the emisora:/grupo: routing. It MUST NOT call playMediaItem, MUST NOT mutate the now-playing mediaItem, and MUST NOT start, stop, restart, or otherwise alter current playback or playback position.

Scenario: User selects a preset while a station is playing

• GIVEN a station is currently playing and projected to the car
• WHEN the user taps an eq_preset:<nombre> item, resolved via playFromMediaId
• THEN the matching preset is applied via the headless-safe apply seam
• AND the currently playing station continues uninterrupted, with no change to playback position or now-playing metadata

Scenario: User selects a preset while nothing is playing

• GIVEN no station is currently playing
• WHEN the user taps an eq_preset:<nombre> item
• THEN the matching preset is applied via the headless-safe apply seam
• AND no playback starts as a result of the selection

Scenario: Unknown or stale preset id

• GIVEN playFromMediaId receives an eq_preset:<nombre> id whose <nombre> matches no entry in the current PresetEcualizador.presets
• WHEN resolution fails to find a matching preset
• THEN the selection is a no-op: no preset is applied, no playback state changes, and no unhandled exception propagates from the handler

Requirement: EQ Preset Persistence and Phone/Car Parity

An EQ preset applied from the car MUST persist as the principal preset, with the same observable outcome as the phone's existing ServicioEcualizador.guardarPrincipal/cambiarPresetPrincipal path, and MUST be reflected on the phone. A principal preset changed on the phone MUST be observable from the car. The exact code path used to reach the headless-safe persistence seam from an Android Auto bind is deferred to sdd-design.

Scenario: Preset applied from the car persists for the phone

• GIVEN the user selects eq_preset:<nombre> from the car head unit
• WHEN the selection is processed
• THEN the preset is persisted as the principal preset
• AND opening the phone's EQ UI afterward shows that preset as the active/principal preset

Scenario: Preset applied from the phone is reflected for the car

• GIVEN the user changes the principal preset from the phone UI
• WHEN the car head unit subsequently observes EQ-related state through the browse/selection surface
• THEN the car-observable state reflects the phone's most recently applied principal preset

Requirement: Active Preset Indication (Optional)

The system MAY indicate the active/principal preset within the Ecualizador folder's rows. Because the legacy MediaBrowserService browsable-item model has no native "selected item" affordance, any indication, if implemented, MUST be conveyed via a row title text convention (e.g. a marker prefix/suffix) rather than assuming a checkmark or selection icon exists. If a reliable title-text convention is too costly to maintain, this requirement MAY instead be satisfied by explicitly not implementing active-preset indication.

Scenario: Active preset is indicated via title convention (if implemented)

• GIVEN the currently applied principal preset is known when Ecualizador's children are built
• WHEN the design's chosen title-text convention is applied
• THEN exactly one of the 6 preset rows' title carries the active-preset marker, uniquely identifying that preset among the 6

Scenario: Active preset indication is out of scope (if not implemented)

• GIVEN the design opts not to implement an active-preset marker
• WHEN the Ecualizador folder's children are built
• THEN all 6 preset rows are returned with their plain preset names, with no partial or inconsistent marking applied

Requirement: Local Music Root Access and Permission Persistence

The system MUST let the user select a local-music root folder via SAF (ACTION_OPEN_DOCUMENT_TREE), persist the granted URI permission, and MUST NOT crash or leave the local-music root folder in a broken state if that permission is later lost or was never granted.

Scenario: User picks a local music root folder

• GIVEN the user opens the local-music setup flow
• WHEN they complete the SAF folder picker and grant access
• THEN the selected folder's URI permission is persisted
• AND the local-music root becomes browsable in Android Auto without re-prompting the picker

Scenario: Persisted permission survives app restart

• GIVEN a local music root was previously picked and its permission persisted
• WHEN the app is restarted (cold start)
• THEN the local-music root remains browsable in Android Auto without re-prompting the SAF picker

Scenario: Permission revoked or never granted

• GIVEN the SAF permission for the local-music root was revoked outside the app, or no root was ever picked
• WHEN the local-music root folder is browsed in Android Auto
• THEN getChildren returns an empty or explanatory list, not an error
• AND the audio handler does not throw or crash

Requirement: Local Music Browsable Tree

The Android Auto browse tree MUST expose a new non-playable local-music root folder alongside the existing station folders. Browsing that root and any nested subfolder MUST recursively mirror the picked SAF folder's structure: subfolders as non-playable carpeta_local:<id> items and audio files as playable pista:<id> items resolving to PistaLocal instances, using the raw filename as the displayed title.

Scenario: Car browses the local-music root

• GIVEN a local music root folder was picked and its permission is valid
• WHEN getChildren is called with the local-music root folder id
• THEN it returns the root's immediate subfolders as carpeta_local:<id> items and audio files as pista:<id> playable items
• AND each playable item's title is the file's raw filename

Scenario: Car browses a nested subfolder

• GIVEN a carpeta_local:<id> folder returned from a prior browse call
• WHEN getChildren is called with that folder id
• THEN it returns that subfolder's own contents (nested folders and/or tracks), recursively mirroring the on-device structure
• AND browsing an empty subfolder returns an empty list, not an error

Requirement: Local Track Playback Reuses Existing Pipeline

Selecting a pista:<id> item MUST resolve to the corresponding PistaLocal and play it through the existing playMediaItem/PluriWaveAudioHandler pipeline, unchanged, including the shared EQ signal chain.

Scenario: User selects a local track

• GIVEN the user taps a pista:<id> playable item on the car head unit
• WHEN playFromMediaId(id) is called
• THEN the id resolves to a PistaLocal and playback starts through the existing playMediaItem internal path
• AND standard transport (play/pause/stop) and fallback album art work as they do for stations

Scenario: EQ still applies to local track playback (regression guard)

• GIVEN a non-flat EQ preset is currently the active/principal preset
• WHEN a pista:<id> item is played
• THEN the audible output passes through the same shared EQ signal chain used for station playback, with no separate or bypassed path for local tracks

Scenario: Unknown or stale track id

• GIVEN playFromMediaId is called with a pista:<id> that no longer resolves to a known PistaLocal
• WHEN resolution fails
• THEN playback does not start and no unhandled exception propagates from the handler

Requirement: Local Music Folder Item Cap and Paging

A local-music folder (root or nested) whose immediate children exceed _maxItemsCarpetaLocal (50) MUST NOT silently truncate the excess items. getChildren MUST return at most 50 items for the requested page, followed by a trailing non-playable, browsable "more" item whenever additional items remain beyond that page. Selecting the "more" item MUST invoke getChildren again and reveal the next page of up to 50 items, continuing until every item in the folder has been reached; no item may be permanently unreachable. A page that exhausts the folder's remaining items MUST NOT include a "more" item. (Previously: folders exceeding 50 immediate children were capped to 50 with the remainder silently dropped; pagination was explicitly out of scope.)

Scenario: Folder exceeds the item cap

• GIVEN a picked or nested local-music folder contains more than 50 immediate children (subfolders and/or tracks combined)
• WHEN getChildren is called with that folder id for the first page
• THEN exactly 50 items are returned for that page, followed by a trailing "more" item
• AND no error or crash occurs, and no item is permanently unreachable

Scenario: Folder has exactly 50 items (boundary)

• GIVEN a local-music folder contains exactly 50 immediate children
• WHEN getChildren is called with that folder id
• THEN all 50 items are returned
• AND no "more" item is appended, since nothing remains to reveal

Scenario: Folder with 51-100 items pages in two steps

• GIVEN a local-music folder contains between 51 and 100 immediate children
• WHEN getChildren is called with that folder id
• THEN the first page returns 50 items plus a trailing "more" item
• AND WHEN the user selects that "more" item, getChildren is invoked again
• THEN it returns the remaining items with no further "more" item, since that is the last page

Scenario: Folder with 100+ items chains across 3+ pages

• GIVEN a local-music folder contains more than 100 immediate children
• WHEN the user repeatedly selects each returned page's "more" item
• THEN each intermediate page returns 50 items plus a trailing "more" item
• AND the final page returns only the remaining items with no "more" item
• AND every item in the folder is reachable through this chain, none dropped

Scenario: Only the requested page's items are resolved into MediaItems

• GIVEN a local-music folder contains more than 50 immediate children
• WHEN getChildren is called for a given page
• THEN only that page's items (at most 50, plus the "more" item) are constructed into full MediaItems (art, resolved title)
• AND items belonging to pages not yet requested are NOT constructed into MediaItems as part of that call

Requirement: Local Music Folder Friendly Name Display

The settings UI MUST display a human-readable label for the picked local-music root folder instead of the raw SAF content:// tree URI. If a friendly name cannot be derived from the persisted URI, the settings UI MUST fall back to a clear, non-empty label rather than showing a broken, blank, or raw-URI value.

Scenario: Folder picked and friendly name derivable

• GIVEN a local-music root folder has been picked and its URI persisted
• WHEN the settings screen displays the current folder
• THEN it shows a human-readable name derived from the folder, not the raw content URI

Scenario: Friendly name cannot be derived

• GIVEN a persisted local-music root URI whose friendly name cannot be derived (e.g. a malformed or unexpected SAF documentId shape)
• WHEN the settings screen displays the current folder
• THEN it falls back to a non-empty, non-broken label instead of an empty or corrupted value

Requirement: Playable Item Metadata

Every playable MediaItem (station) MUST include a non-empty title and a loadable artUri. Stations without a logo MUST fall back to on-brand artwork, and stations whose logo URL cannot actually be loaded MUST degrade to the same on-brand fallback instead of rendering broken or blank art. The fallback MUST be visually consistent with the phone UI's per-station rotation rather than a generic launcher-icon copy. (Previously: fallback only covered a null/empty favicon and pointed at a bundled default-artwork asset that read as a copy of the launcher icon.)

Scenario: Station has a valid, reachable remote logo

• GIVEN a station has a remote logo URL that resolves to a loadable image
• WHEN it is mapped to a MediaItem
• THEN title is the station name and artUri is the station's logo URL

Scenario: Station has no logo (Case A)

• GIVEN a station has no logo (favicon is null or empty)
• WHEN it is mapped to a MediaItem
• THEN artUri is set to one of the on-brand station_art_* fallback assets instead of being empty or null

Scenario: Station's logo URL is present but unreachable (Case B)

• GIVEN a station has a non-empty favicon URL that cannot be loaded (dead link, unreachable host, or non-image response)
• WHEN it is mapped to (or resolved as) a MediaItem in the Android Auto browse tree
• THEN the system SHALL show the same on-brand fallback art used for Case A instead of broken or blank art
• AND the car head unit MUST NOT display an empty, broken-image, or indefinitely-loading art tile for that station

Scenario: Fallback art matches phone-UI per-station selection

• GIVEN a station falls back to on-brand art (Case A or Case B)
• WHEN the fallback asset is chosen for that station
• THEN the selected asset MUST be one of the same 4 rotating assets used by the phone UI (station_art_aurora, station_art_cosmic, station_art_pulse, station_art_nova)
• AND the same station MUST deterministically resolve to the same asset on both the phone UI and Android Auto (per-station selection parity), not a random or session-varying choice

Scenario: Fallback art is on-brand, not the launcher icon

• GIVEN a station requires fallback art (Case A or Case B)
• WHEN its artUri is resolved
• THEN it MUST NOT point at a byte-for-byte copy of the app launcher icon
• AND it MUST point at one of the 4 on-brand station_art_* assets

Requirement: Media Item Resolution by ID

getMediaItem MUST resolve a single station id to its full MediaItem, returning null for unknown ids instead of throwing.

Scenario: Known station id

• GIVEN a valid station id that exists in current state
• WHEN getMediaItem(id) is called
• THEN it returns the corresponding MediaItem with title and artUri populated

Scenario: Unknown station id

• GIVEN an id that does not match any known station or folder
• WHEN getMediaItem(id) is called
• THEN it returns null without throwing

Requirement: Play by Media ID Reuses Existing Playback Path

playFromMediaId MUST resolve the id to an Emisora and invoke the existing internal playMediaItem path; it MUST NOT duplicate playback or reconnection logic.

Scenario: User selects a station in the car

• GIVEN the user taps a playable station item on the car head unit
• WHEN playFromMediaId(id) is called
• THEN the id is resolved to an Emisora via the existing resolution logic (_emisoraDesdeMediaItem)
• AND playback starts through the existing playMediaItem internal path
• AND no separate or duplicated playback logic is executed

Scenario: Unknown or stale media id

• GIVEN playFromMediaId is called with an id that no longer resolves to a known station
• WHEN resolution fails
• THEN playback does not start and no unhandled exception propagates from the handler

Requirement: Playback State Synchronization

Play/pause/stop state changes MUST remain synchronized between the car head unit and the phone UI, regardless of which side initiated the change.

Scenario: User pauses from the car

• GIVEN a station is playing and projected to the car
• WHEN the user pauses from the car head unit
• THEN the phone UI reflects the paused state via the shared MediaSession/PlaybackState

Scenario: User pauses from the phone

• GIVEN a station is playing and projected to the car
• WHEN the user pauses from the phone UI
• THEN the car head unit reflects the paused state via the same shared session