src/devices/tv/index.jd

page.title=TV Input Framework
@jd:body

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    <h2>In this document</h2>
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<h2 id=introduction>Introduction</h2>

<p>The Android TV Input Framework (TIF) simplifies the delivery of live content to
Android TV. The Android TIF provides a standard API for manufacturers to use to
create input modules for controlling Android TV. It also 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.</p>

<p>The Android TIF makes it easier for partners to meet regional digital TV
broadcast standards without re-implementation. This document may also inform
third-party app developers who would like to create custom TV Inputs.</p>

<h2 id=components>Components</h2>

<p>The Android TV Input Framework implementation includes a TV Input Manager and
an example TV App that works with a special remote control 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.</p>

<p>The TV Input Framework consists of:</p>

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

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

<img src="images/TIF_Overview.png" alt="Overview of the Android TIF architecture">
<p class="img-caption"><strong>Figure 1.</strong> Android TV Input Framework (TIF) architecture</p>

<h2 id=flow>Flow</h2>

<p>Here is how the architecture is exercised:</p>

<ol>
  <li>The user sees and interacts with the TV App, a system app that can’t be
replaced by a third-party app. The Android Open Source Project (AOSP) provides
a reference TV App that manufacturers can extend to suit their needs.
  <li>The TV App displays the AV content from the TV Input.
  <li>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 <em>TV Input Manager</em> below for more details about these limitations.
</ol>

<h2 id=permissions>Permissions</h2>

<ul>
  <li>Only <code><a
href="http://developer.android.com/guide/topics/manifest/permission-element.html#plevel">signatureOrSystem</a></code>
TV Inputs and TV App have full access to the TV Provider database and are able
to receive KeyEvents.
  <li>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.
  <li>Third-party TV Inputs have package-locked access to the TV Provider database
and can READ/WRITE only to matching package rows.
  <li>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.
  <li><code>TV_INPUT_HARDWARE</code> 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.
</ul>

<h2 id=tv_provider>TV Provider</h2>

<p>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. </p>

<p>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 <code>android.provider.TvContract.Genres</code>. 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 <code>android.provider.TvContract.Genres.SPORTS</code>.</p>

<p>See the diagram below for a detailed view of the TV Provider. </p>

<img src="images/TIF_TV_Provider.png" alt="Android TV Provider">
<p class="img-caption"><strong>Figure 2.</strong> Android TV Provider</p>

<p><em>Only apps in the privileged system partition can read the entire TV Provider
database. </em></p>

<p>Passthrough TV inputs do not store channels and programs. </p>

<p>In addition to the standard fields for channels and programs, the TV Provider
database also offers a BLOB type field, <code>COLUMN_INTERNAL_PROVIDER_DATA</code>, 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).</p>

<h3 id=tv_provider_database_field_examples>Database field examples</h3>

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

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

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

<h3 id=permissions_and_access_control>Permissions and access control</h3>

<p>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.</p>

<ul>
  <li>Each row has <code>PACKAGE_NAME</code>, 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.
  <li>READ, WRITE permissions via AndroidManifest.xml (requires user consent) to
determine available channels.
  <li>Only <code>signatureOrSystem</code> apps can acquire <code>ACCESS_ALL_EPG_DATA</code> permission to access the entire database.
</ul>

<h2 id=tv_input_manager>TV Input Manager</h2>

<p>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:</p>

<ul>
  <li>List TV inputs and check their status
  <li>Create sessions and manage listeners
</ul>

<p>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 <code>TvContract.buildChannelUriForPassthroughInput()</code>. 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.</p>

<p>An app may create and register a <code>TvInputCallback</code> with the <code>android.media.tv.TvInputManager</code> 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.</p>

<p>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
partners to create their own TV Apps while helping all third-party TV Inputs
work on all TV Apps, thus creating an ecosystem. </p>

<h2 id=tv_inputs>TV Inputs</h2>

<p>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. </p>

<p>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.</p>

<h3 id=passthrough_input_example>Passthrough input example</h3>

<img src="images/TIF_HDMI_TV_Input.png" alt="Android TV System Input">
<p class="img-caption"><strong>Figure 3.</strong> Android TV System Input</p>

<p>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 <code>android.media.tv.TvContract</code> utility method <code>buildChannelUriForPassthroughInput(String inputId)</code>.  The TV App communicates with the TV Input Manager to reach the HDMI TV
Input. </p>

<h3 id=built-in_tuner_example>Built-in tuner example</h3>

<img src="images/Built-in_Tuner_TV_Input.png" alt="Android TV Built-in Tuner Input">
<p class="img-caption"><strong>Figure 4.</strong> Android TV Built-in Tuner Input</p>

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

<h3 id=third-party_input_example>Third-party input example</h3>

<img src="images/Third-party_Input_HDMI.png" alt="Android TV third-party input">
<p class="img-caption"><strong>Figure 5.</strong> Android TV third-party input</p>

<p>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.</p>

<p>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.</p>

<h3 id=picture_in_picture_pip_example>Picture in picture (PIP) example </h3>

<img src="images/TIF_PIP-PAP.png" alt="Android TV KeyEvents">
<p class="img-caption"><strong>Figure 6.</strong> Android TV KeyEvents</p>

<p>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 <a href="http://source.android.com/devices/tech/input/overview.html">input pipeline</a> <code>InputReader</code> and <code>InputDispatcher</code> functions as <a href="http://developer.android.com/reference/android/view/KeyEvent.html">KeyEvents</a>. These in turn trigger events on the TV App if it is in focus. </p>

<p>Only system TV Inputs are eligible to receive <code>InputEvents</code>, and only if they have the <code>RECEIVE_INPUT_EVENT</code> 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.</p>

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

<h3 id=mheg-5_input_example>MHEG-5 input example</h3>

<p>The following diagram shows a more detailed view of how <code>KeyEvents</code> are routed through the Android TIF.</p>

<img src="images/TIF_MHEG5_app.png" alt="Android TV Red button example">
<p class="img-caption"><strong>Figure 7.</strong> Android TV Red button example</p>

<p>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.</p>

<p>See the <em>Broadcast app</em> section to learn how broadcast apps interact with the TV App.</p>

<p>In this example:</p>

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

<p class="note"><strong>Note</strong>: Third-party TV inputs never receive keys. </p>

<h2 id=tv_input_hal>TV Input HAL</h2>

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

<h2 id=tv_app>TV App</h2>

<p>The Android TV Input Framework includes a reference implementation to help
manufacturers create their own TV Apps more quickly.  Third-party developers
cannot develop TV Apps as the APIs require system or signature permission.</p>

<p>Partners are strongly encouraged to take the reference as a base implementation
and extend it to add additional functionality. By building upon the reference
implementation, bug fixes and improvements added to the reference will be more
easily included in the partner’s variant. By extending the TV App in a
structured way, it is easier to pick up new features and bug fixes made to the
reference. Ideally, those extensions are submitted to the Android ecosystem so
others may benefit from and be compatible with them.</p>

<p>The TV App provides channel and program search results (via <code>com.android.tv.search.TvProviderSearch</code>) 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.</p>

<p>The example Android TV App lets manufacturers see how the TIF works and should
expedite their own development by demonstrating a simple TV-watching
experience. </p>

<p>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:</p>

<h3 id=setup_and_configuration>Setup and configuration</h3>

<ul>
  <li>Auto-detect TV Inputs
  <li>Let TV Inputs initiate channel setup
  <li>Control parental settings
  <li>Alter TV settings
  <ul>
    <li>Edit channel
  </ul>
</ul>

<h3 id=viewing>Viewing</h3>
<ul>
  <li>Access and navigate all TV channels
  <li>Access TV program information bar
  <li>Multiple audio and subtitle track support
  <li>Parental control PIN challenge
  <li>Allow TV Input UI overlay for:
  <ul>
    <li>TV standard (HbbTV, etc.)
  </ul>
</ul>

<h2 id=parental_control>Parental Control</h2>

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

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

<h3 id=tv_provider>TV Provider</h3>

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

<h3 id=tv_input_manager>TV Input Manager</h3>

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

<h3 id=tv_input>TV Input</h3>

<p>The TV Input checks if the current content should be blocked by calling <code>isRatingBlocked()</code> 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 <code>ACTION_BLOCKED_RATINGS_CHANGED</code> and <code>ACTION_PARENTAL_CONTROLS_ENABLED_CHANGED</code>). 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 <code>notifyContentBlocked(TvContentRating)</code>.</p>

<h3 id=tv_app>TV App</h3>

<p>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.</p>

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

<h2 id=hdmi-cec>HDMI-CEC</h2>

<p>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.</p>

<p>The Android TIF implements HDMI-CEC as the HDMI Control Service so that
partners 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.</p>

<p>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.</p>

<img src="images/TV_App_CEC_integration.png" alt="CEC integration on Android TV">
<p class="img-caption"><strong>Figure 8.</strong> CEC integration on Android TV</p>

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

<h2 id=tv_integration_guidelines>TV integration guidelines</h2>

<h3 id=broadcast_app>Broadcast app</h3>

<p>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:</p>

<ul>
  <li> MHEG: native stack
  <li> Teletext: native stack
  <li> HbbTV: webkit modification by Opera browser
</ul>

<p>In the Android L release, Android TV expects partners 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.</p>

<p>Here’s how the broadcast app and TV App interact:</p>

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

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

<h3 id=dvr>DVR</h3>

<p>Android TV supports digital video recording (DVR) with partner development. The
DVR function works like so:</p>

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

<p>For voice search/recommendation:</p>

<ul>
  <li>DVR app supports In-app search for Voice search.
  <li>DVR app can propose recommendation using notifications.
</ul>

<p>See the following diagram for a view into a possible DVR implementation in
Android TV.</p>

<img src="images/TV_Input_DVR.png" alt="Digital video recording in Android TV">
<p class="img-caption"><strong>Figure 9.</strong> Digital video recording in Android TV</p>