TV Input Framework

The Android TV Input Framework (TIF) simplifies delivery of live content to Android TV. The Android TIF provides a standard API for manufacturers to create input modules for controlling Android TV, and enables live TV search and recommendations via metadata published by the TV Input.

The framework does not seek to implement TV standards or regional requirements, but does makes it easier for device manufacturers to meet regional digital TV broadcast standards without re-implementation. Documentation in this section might also be useful to third-party app developers who want to create custom TV Inputs.

Components

The Android TV Input Framework implementation includes a TV Input Manager. The TIF works with the TV App, a system app that can’t be replaced by a third-party app, to access built-in and IP tuner channels. The TV App communicates with TV Input modules supplied by the device manufacturer or other parties through the TV Input Manager.

The TV Input Framework consists of:

• TV Provider (com.android.providers.tv.TvProvider): a database of channels, programs, and associated permissions
• TV App (com.android.tv.TvActivity): the app that handles user interaction
• TV Input Manager (android.media.tv.TvInputManager): allows the TV Inputs to communicate with the TV App
• TV Input: an app representing physical or virtual tuners and input ports
• TV Input HAL (tv_input module): a hardware definition that allows system TV Inputs to access TV-specific hardware when implemented
• Parental Control: the technology to allow blocking of channels and programs
• HDMI-CEC: the technology to allow remote control of various devices over HDMI

These components are covered in detail below. See the following diagram for a detailed view of the Android TV Input Framework architecture.

Figure 1. Android TV Input Framework (TIF) architecture

Flow

Here is how the architecture is exercised:

1. The user sees and interacts with the TV App, a system app that can’t be replaced by a third-party app.
2. The TV App displays the AV content from the TV Input.
3. The TV App cannot talk directly with the TV Inputs. The TV Input Manager identifies the state of TV Inputs for the TV App. See TV Input Manager below for more details about these limitations.

Permissions

• Only signatureOrSystem TV Inputs and TV App have full access to the TV Provider database and are able to receive KeyEvents.
• Only system TV Inputs can access the TV Input HAL through the TV Input Manager service. TV Inputs are accessed one-to-one via TV Input Manager sessions.
• Third-party TV Inputs have package-locked access to the TV Provider database and can READ/WRITE only to matching package rows.
• Third-party TV inputs can either display their own content or content from a device manufacturer’s passthrough TV inputs, like HDMI1. They can’t display content from non-passthrough TV inputs, like a built-in or IPTV tuner.
• TV_INPUT_HARDWARE permission for a hardware TV Input app, signals the TV Input Manager Service to notify the TV Input service on boot to call the TV Input Manager Service and add its TV Inputs. This permission allows a hardware TV Input app to support multiple TV Inputs per TV Input service, as well as being able to dynamically add and remove its supported TV Inputs.

TV Provider

The TV Provider database stores the channels and programs from TV Inputs. The TV Provider also publishes and manages the associated permissions so that TV Inputs can see only their own records. For instance, a specific TV Input can see only the channels and programs it has supplied and is prohibited from accessing any other TV Inputs’ channels and programs.

The TV Provider maps "broadcast genre" to "canonical genre" internally. TV Inputs are responsible for populating "broadcast genre" with the value in the underlying broadcast standard, and the "canonical genre" field will automatically be populated with the correct associated genre from android.provider.TvContract.Genres. For example, with broadcast standard ATSC A/65 and program with genre 0x25 (meaning “Sports”), the TV Input will populate the “broadcast genre” with the String “Sports” and TV Provider will populate the “canonical genre” field with the mapped value android.provider.TvContract.Genres.SPORTS.

See the diagram below for a detailed view of the TV Provider.

Figure 2. Android TV Provider

Only apps in the privileged system partition can read the entire TV Provider database.

Passthrough TV inputs do not store channels and programs.

In addition to the standard fields for channels and programs, the TV Provider database also offers a BLOB type field, COLUMN_INTERNAL_PROVIDER_DATA, in each table that TV Inputs may use to store arbitrary data. That BLOB data can include custom information, such as frequency of the associated tuner, and may be provided in a protocol buffer or another form. A Searchable field is available to make certain channels unavailable in search (such as to meet country-specific requirements for content protection).

Database field examples

The TV Provider supports structured data in channel (android.provider.TvContract.Channels) and program (android.provider.TvContract.Programs) tables. These tables are populated and accessed by TV Inputs and system apps like the TV App. These tables have four types of fields:

• Display: Display fields contain information that apps may want to make visible to the user, like a channel’s name (COLUMN_DISPLAY_NAME) or number (COLUMN_DISPLAY_NUMBER), or the title of the program being viewed.
• Metadata: There are three fields for identifying content, according to relevant standards, like a channel’s transport stream ID (COLUMN_TRANSPORT_STREAM_ID), original network ID (COLUMN_ORIGINAL_NETWORK_ID) and service id (COLUMN_SERVICE_ID).
• Internal data: Fields that are for the custom use of TV Inputs.
  Some fields, like COLUMN_INTERNAL_PROVIDER_DATA, are customizable BLOB fields where a TV Input can store arbitrary metadata about their channel or program.
• Flag: Flag fields represent whether a channel should be restricted from search, browse, or viewing. This can be set only at the channel level. All programs defer to the setting on the channel.
  • COLUMN_SEARCHABLE: Restricting search from some channels may be a requirement in certain regions. COLUMN_SEARCHABLE = 0 means the channel should not be exposed in search results.
  • COLUMN_BROWSABLE: Visible to system applications only. Restricting channel from being browsed by applications. COLUMN_BROWSABLE = 0 means the channel should not be included in the channel list.
  • COLUMN_LOCKED: Visible to system applications only. Restricting channel from being viewed by invalid accounts without entering PIN code. COLUMN_LOCKED = 1 means the channel should be protected by parental control.

For a more exhaustive list of the fields, see android/frameworks/base/media/java/android/media/tv/TvContract.java

Permissions and access control

All fields are visible to anyone with access to the corresponding row. No fields are directly accessible to users; they see only what the TV App, System apps, or TV Inputs surface.

• Each row has PACKAGE_NAME, the package (app) that owns that row, checked on Query, Insert, Update via TvProvider.java. A TV Input may access only the information it wrote and is cordoned off from the information provided by other TV Inputs.
• READ, WRITE permissions via AndroidManifest.xml (requires user consent) to determine available channels.
• Only signatureOrSystem apps can acquire ACCESS_ALL_EPG_DATA permission to access the entire database.

TV Input Manager

The TV Input Manager provides a central system API to the overall Android TV Input Framework. It arbitrates interaction between apps and TV Inputs and provides parental control functionality. TV Input Manager sessions must be created one-to-one with TV Inputs. The TV Input Manager allows access to installed TV Inputs so apps may:

• List TV inputs and check their status
• Create sessions and manage listeners

For sessions, a TV Input may be tuned by the TV App only to URIs it has added to the TV Provider database, except for passthrough TV Inputs which can be tuned to using TvContract.buildChannelUriForPassthroughInput(). A TV Input may also have its volume set. TV Inputs provided and signed by the device manufacturer (signature apps) or other apps installed in the system partition will have access to the entire TV Provider database. This access can be used to construct apps to browse and search across all available TV channels and programs.

An app may create and register a TvInputCallback with the android.media.tv.TvInputManager to be called back on a TV Input’s state change or on the addition or removal of a TV Input. For example, a TV App can react when a TV Input is disconnected by displaying it as disconnected and preventing its selection.

The TV Input Manager abstracts communication between the TV App and TV Inputs. The standard interface of TV Input Manager and TV Input allows multiple device manufacturers to create their own TV Apps while helping all third-party TV Inputs work on all TV Apps.

TV Inputs

TV Inputs are Android apps in the sense they have an AndroidManifest.xml and are installed (via Play, pre-installed, or sideloaded). Android TV supports pre-installed system apps, apps signed by the device manufacturer and third-party TV Inputs.

Some inputs, like the HDMI input or built-in tuner input, can be provided only by the manufacturer as they speak directly with the underlying hardware. Others, such as IPTV, place-shifting, and external STB, can be supplied by third parties as APKs on Google Play Store. Once downloaded and installed, the new input can be selected within the TV App.

Passthrough input example

Figure 3. Android TV System Input

In this example, the TV Input provided by the device manufacturer is trusted and has full access to the TV Provider. As a passthrough TV Input, it does not register any channels or programs with the TV Provider. To obtain the URI used to reference the passthrough input, use the android.media.tv.TvContract utility method buildChannelUriForPassthroughInput(String inputId). The TV App communicates with the TV Input Manager to reach the HDMI TV Input.

Built-in tuner example

Figure 4. Android TV Built-in Tuner Input

In this example, the Built-in Tuner TV Input provided by the device manufacturer is trusted and has full access to the TV Provider.

Third-party input example

Figure 5. Android TV third-party input

In this example, the external STB TV Input is provided by a third party. Since that TV Input can’t directly access the HDMI video feed coming in, it must go through the TV Input Manager and use the HDMI TV Input provided by the device manufacture.

Through the TV Input Manager, the external STB TV Input can speak with the HDMI TV Input and ask it to show the video on HDMI1. So the STB TV Input can control the TV while the manufacturer-provided HDMI TV Input renders the video.

Picture in picture (PIP) example

Figure 6. Android TV KeyEvents

The diagram above shows how buttons on a remote control are passed to a specific TV Input for picture in picture (PIP) display. Those button presses are interpreted by the hardware driver supplied by the device manufacturer, converting hardware scancodes to Android keycodes and passing them to the standard Android input pipeline InputReader and InputDispatcher functions as KeyEvents. These in turn trigger events on the TV App if it is in focus.

Only system TV Inputs are eligible to receive InputEvents, and only if they have the RECEIVE_INPUT_EVENT system permission. The TV Input is responsible to determine which InputEvents to consume and should allow the TV App to handle the keys it does not need to consume.

The TV App is responsible for knowing which system TV Input is active, meaning selected by the user, and to disambiguate incoming KeyEvents and route them to the correct TV Input Manager session, calling dispatchInputEvent() to pass on the event to the associated TV Input.

MHEG-5 input example

The following diagram shows a more detailed view of how KeyEvents are routed through the Android TIF.

Figure 7. Android TV Red button example

It depicts the flow of a Red button app, common in Europe for letting users access interactive apps on their televisions. An app can be delivered over this transport stream. When the button is clicked, it lets users interact with these broadcast apps. For example, you might use these broadcast apps to access related web pages or sports scores.

See the Broadcast app section to learn how broadcast apps interact with the TV App.

In this example:

1. The TV App is in focus and receives all keys.
2. KeyEvents (e.g. the Red button) is passed to the active TV Input as InputEvents.
3. The system TV Input integrates with MHEG-5 stack and has the RECEIVE_INPUT_EVENT system permission.
4. On receiving activation keycode (e.g. Red button), the TV Input activates broadcast app.
5. TV input consumes KeyEvents as InputEvents and the broadcast app is the focus and handles InputEvents until dismissed.

Note: Third-party TV inputs never receive keys.

TV Input HAL

The TV Input HAL aids development of TV Inputs to access TV-specific hardware. As with other Android HALs, the TV Input HAL (tv_input) is available in the AOSP source tree and the vendor develops its implementation.

TV App

The TV App provides channel and program search results (via com.android.tv.search.TvProviderSearch) and passes keys, tune, and volume calls to TV Inputs through the TV Input Manager. Manufacturers must implement the TV App to ensure search functions work for their users. Otherwise, users will struggle to navigate the resulting Android TV. Third-party developers cannot develop TV Apps as the APIs require system or signature permission.

As with the TIF in general, the TV App does not seek to implement device manufacturer or country-specific features. Instead, it handles these tasks by default:

Setup and configuration

• Auto-detect TV Inputs
• Let TV Inputs initiate channel setup
• Control parental settings
• Alter TV settings
  • Edit channel

Viewing

• Access and navigate all TV channels
• Access TV program information bar
• Multiple audio and subtitle track support
• Parental control PIN challenge
• Allow TV Input UI overlay for:
  • TV standard (HbbTV, etc.)

Parental Control

Parental control lets a user block undesired channels and programs, but bypass the block by entering a PIN code.

Responsibility for parental control functionality is shared amongst the TV App, TV Input Manager service, TV Provider, and TV Input.

TV Provider

Each channel row has a COLUMN_LOCKED field that is used to lock specific channels from viewing without entering a PIN code. The program field COLUMN_CONTENT_RATING is intended for display and is not used to enforce parental control.

TV Input Manager

The TV Input Manager stores every blocked TvContentRating and responds to isRatingBlocked() to advise if content with the given rating should be blocked.

TV Input

The TV Input checks if the current content should be blocked by calling isRatingBlocked() on the TV Input Manager when the rating of the displayed content has changed (on program or channel change), or parental control settings have changed (on ACTION_BLOCKED_RATINGS_CHANGED and ACTION_PARENTAL_CONTROLS_ENABLED_CHANGED). If the content should be blocked, the TV Input disables the audio and video and notifies the TV app that the current content is blocked by calling notifyContentBlocked(TvContentRating). If the content should not be blocked, the TV Input enables audio and video and notifies the TV App the current content is allowed by calling notifyContentAllowed().

TV App

The TV App shows parental control settings to users and a PIN code UI when it is notified by a TV Input that the current content is blocked or when the user attempts to view a blocked channel.

The TV App does not directly store the parental control settings. When the user changes the parental control settings, every blocked TvContentRating is stored by the TV Input Manager, and blocked channels are stored by the TV Provider.

HDMI-CEC

HDMI-CEC allows one device to control another, thereby enabling a single remote to control multiple appliances in a home theater. It is used by Android TV to speed setup and allow distant control over various TV Inputs via the central TV App. For instance, it may switch inputs, power up or down devices, and more.

The Android TIF implements HDMI-CEC as the HDMI Control Service so that device manufacturers merely need to develop low-level drivers that interact with the lightweight Android TV HAL, skipping more complex business logic. In providing a standard implementation, Android seeks to mitigate compatibility issues by reducing fragmented implementations and selective feature support. The HDMI Control Service uses the existing Android services, including input and power.

This means existing HDMI-CEC implementations will need to be redesigned to interoperate with the Android TIF. We recommend the hardware platform contain a microprocessor to receive CEC power on and other commands.

Figure 8. CEC integration on Android TV

1. The CEC bus receives a command from the currently active source to switch to a different source.
2. The driver passes the command to the HDMI-CEC HAL.
3. The HAL notifies all ActiveSourceChangeListeners.
4. THe HDMI Control Service is notified of source change via ActiveSourceChangeListener.
5. The TV Input Manager service generates an intent for the TV App to switch the source.
6. The TV App then creates a TV Input Manager Session for the TV Input being switched to and calls setMain on that session.
7. The TV Input Manager Session passes this information on to the HDMI TV Input.
8. The HDMI TV input requests to set sideband surface.
9. The TV Input Manager Service generates a corresponding routing control command back to HDMI Control Service when the surface is set.

TV integration guidelines

Broadcast app

Because each country has broadcast-specific requirements (MHEG, Teletext, HbbTV, and more), manufacturers are expected to supply their own solutions for the broadcast app, for example:

• MHEG: native stack
• Teletext: native stack
• HbbTV: webkit modification by Opera browser

In the Android L release, Android TV expects device manufacturers to use systems integrators or the Android solutions for regional TV stacks, pass the surface to TV software stacks, or pass the necessary key code to interact with legacy stacks.

Here’s how the broadcast app and TV App interact:

1. The TV App is in focus, receiving all keys.
2. The TV App passes keys (e.g. Red button) to the TV Input device.
3. The TV Input device internally integrates with legacy TV stack.
4. On receiving an activation keycode (e.g. Red button), the TV Input device activates broadcast apps.
5. A broadcast app takes focus in the TV App and handles user actions.

For voice search/recommendation, the broadcast app may support In-app search for voice search.

DVR

Android TV supports digital video recording (DVR) with device manufacturer development. The DVR function works like so:

1. DVR recording function / Live Buffer can be implemented by any TV Input.
2. TV App passes on key inputs to TV Input (including recording/pause/fast forward/ rewind keys).
3. When playing the recorded content, the TV Input handles it with trick play overlay.
4. DVR app enables users to browse and manage recorded program.

For voice search/recommendation:

• DVR app supports In-app search for Voice search.
• DVR app can propose recommendation using notifications.

See the following diagram for a view into a possible DVR implementation in Android TV.

Figure 9. Digital video recording in Android TV