AIR for TV application design considerations

Video considerations

Video encoding guidelines

When streaming video to a TV device, Adobe recommends the following encoding guidelines:

Video codec:

H.264, Main or High profile, progressive encoding

Resolution:

720i, 720p, 1080i, or 1080p

Frame rate:

24 frames per second or 30 frames per second

Audio codec:

AAC-LC or AC-3, 44.1 kHz, stereo, or these multichannel audio codecs: E-AC-3, DTS, DTS Express, DTS-HD High Resolution Audio, or DTS-HD Master Audio

Combined bit rate:

up to 8M bps depending on available bandwidth

Audio bit rate:

up to 192 Kbps

Pixel aspect ratio:

1 × 1

Adobe recommends that you use the H.264 codec for video delivered to AIR for TV devices.

Note: AIR for TV also supports video that is encoded with Sorenson Spark or On2 VP6 codecs. However, the hardware does not decode and present these codecs. Instead, the runtime decodes and presents these codecs using software, and therefore, the video plays at a much lower frame rate. Therefore, use H.264 if at all possible.

The StageVideo class

AIR for TV supports hardware decoding and presentation of H.264-encoded video. Use the StageVideo class to enable this feature.

See Using the StageVideo class for hardware accelerated presentation in the ActionScript 3.0 Developer’s Guide for details about:

  • the API of the StageVideo class and related classes.

  • limitations of using the StageVideo class.

To best support existing AIR applications that use the Video object for H.264-encoded video, AIR for TV internally uses a StageVideo object. Doing so means the video playback benefits from hardware decoding and presentation. However, the Video object is subject to the same restrictions as a StageVideo object. For example, if the application tries to rotate the video, no rotation occurs, since the hardware, not the runtime, is presenting the video.

However, when you write new applications, use the StageVideo object for H.264-encoded video.

For an example of using the StageVideo class, see Delivering video and content for the Flash Platform on TV.

Video delivery guidelines

On an AIR for TV device, the network’s available bandwidth can vary during video playback. These variations can occur, for example, when another user starts to use the same Internet connection.

Therefore, Adobe recommends that your video delivery system use adaptive bitrate capabilities. For example, on the server side, Flash Media Server supports adaptive bitrate capabilities. On the client side, you can use the Open Source Media Framework (OSMF).

The following protocols are available to deliver video content over the network to an AIR for TV application:
  • HTTP and HTTPS Dynamic Streaming (F4F format)

  • RTMP, RTMPE, RTMFP, RTMPT, and RTMPTE Streaming

  • HTTP and HTTPS Progressive Download

For more information, see the following:

Audio considerations

The ActionScript for playing sound is no different in AIR for TV applications than in other AIR applications. For information, see Working with sound in the ActionScript 3.0 Developer’s Guide.

Regarding multichannel audio support in AIR for TV, consider the following:

  • AIR for TV supports multichannel audio for videos that are progressively downloaded from an HTTP server. Support for multichannel audio in videos streamed from an Adobe Flash Media Server is not yet available.

  • Although AIR for TV supports many audio codecs, not all AIR for TV devices support the entire set. Use the flash.system.Capabilities method hasMultiChannelAudio()to check whether an AIR for TV device supports a particular multichannel audio codec such as AC-3.

    For example, consider an application that progressively downloads a video file from a server. The server has different H.264 video files that support different multichannel audio codecs. The application can use hasMultiChannelAudio()to determine which video file to request from the server. Alternatively, the application can send a server the string contained in Capabilities.serverString. The string indicates which multichannel audio codecs are available, allowing the server to select the appropriate video file.

  • When using one of the DTS audio codecs, scenarios exist in which hasMultiChannelAudio() returns true, but the DTS audio is not played.

    For example, consider a Blu-ray player with an S/PDIF output, connected to an old amplifier. The old amplifier does not support DTS, but S/PDIF has no protocol to notify the Blu-ray player. If the Blu-ray player sends the DTS stream to the old amplifier, the user hears nothing. Therefore, as a best practice when using DTS, provide a user interface so that the user can indicate if no sound is playing. Then, your application can revert to a different codec.

The following table summarizes when to use different audio codecs in AIR for TV applications. The table also indicates when AIR for TV devices use hardware accelerators to decode an audio codec. Hardware decoding improves performance and offloads the CPU.

Audio codec

Availability on AIR for TV device

Hardware decoding

When to use this audio codec

More information

AAC

Always

Always

In videos encoded with H.264.

For audio streaming, such as an Internet music streaming service.

When using an audio-only AAC stream, encapsulate the audio stream in an MP4 container.

mp3

Always

No

For sounds in the application’s SWF files.

In videos encoded with Sorenson Spark or On2 VP6.

An H.264 video that uses mp3 for the audio does not play on AIR for TV devices.

AC-3 (Dolby Digital)

E-AC-3 (Enhanced Dolby Digital)

DTS Digital Surround

DTS Express

DTS-HD High Resolution Audio

DTS-HD Master Audio

Check

Yes

In videos encoded with H.264.

Typically, AIR for TV passes a multichannel audio stream to an external audio/video receiver which decodes and plays the audio.

Speex

Always

No

Receiving a live voice stream.

An H.264 video that uses Speex for audio does not play on AIR for TV devices. Use Speex only with Sorenson Spark or On2 VP6 encoded videos.

NellyMoser

Always

No

Receiving a live voice stream.

An H.264 video that uses NellyMoser for audio does not play on AIR for TV devices. Use NellyMoser only with Sorenson Spark or On2 VP6 encoded videos.

Note: Some video files contain two audio streams. For example, a video file can contain both an AAC stream and an AC3 stream. AIR for TV does not support such video files, and using such a file can result in no sound for the video.

Graphics hardware acceleration

Using hardware graphics acceleration

AIR for TV devices provide hardware acceleration for 2D graphics operations. The device’s hardware graphics accelerators off-load the CPU to perform the following operations:

  • Bitmap rendering

  • Bitmap scaling

  • Bitmap blending

  • Solid rectangle filling

This hardware graphics acceleration means many graphics operations in an AIR for TV application can be high performing. Some of these operations include:

  • Sliding transitions

  • Scaling transitions

  • Fading in and out

  • Compositing multiple images with alpha

To get the performance benefits of hardware graphics acceleration for these types of operations, use one of the following techniques:

  • Set the cacheAsBitmap property to true on MovieClip objects and other display objects that have content that is mostly unchanging. Then perform sliding transitions, fading transitions, and alpha blending on these objects.

  • Use the cacheAsBitmapMatrix property on display objects you want to scale or translate (apply x and y repositioning).

    By using Matrix class operations for scaling and translation, the device’s hardware accelerators perform the operations. Alternatively, consider the scenario where you change the dimensions of a display object that has its cacheAsBitmap property set to true. When the dimensions change, the runtime’s software redraws the bitmap. Redrawing with software yields poorer performance than scaling with hardware acceleration by using a Matrix operation.

    For example, consider an application that displays an image that expands when an end user selects it. Use the Matrix scale operation multiple times to give the illusion of the image expanding. However, depending on the size of the original image and final image, the quality of the final image can be unacceptable. Therefore, reset the dimensions of the display object after the expanding operations are completed. Because cacheAsBitmap is true, the runtime software redraws the display object, but only once, and it renders a high-quality image.

    Note: Typically, AIR for TV devices do not support hardware-accelerated rotation and skewing. Therefore, if you specify rotation and skewing in the Matrix class, AIR for TV performs all the Matrix operations in the software. These software operations can have a detrimental impact to performance.
  • Use the BitmapData class to create custom bitmap caching behavior.

For more information about bitmap caching, see the following:

Managing graphics memory

To perform the accelerated graphics operations, hardware accelerators use special graphics memory. If your application uses all the graphics memory, the application runs more slowly because AIR for TV reverts to using software for the graphics operations.

To manage your application’s use of graphics memory:

  • When you are done using an image or other bitmap data, release its associated graphics memory. To do so, call the dispose() method of the bitmapData property of the Bitmap object. For example:

    myBitmap.bitmapData.dispose();
    Note: Releasing the reference to the BitmapData object does not immediately free the graphics memory. The runtime’s garbage collector eventually frees the graphics memory, but calling dispose() gives your application more control.
  • Use PerfMaster Deluxe, an AIR application that Adobe provides, to better understand hardware graphics acceleration on your target device. This application shows the frames per second to execute various operations. Use PerfMaster Deluxe to compare different implementations of the same operation. For example, compare moving a bitmap image versus moving a vector image. PerfMaster Deluxe is available at Flash Platform for TV.

Managing the display list

To make a display object invisible, set the object’s visible property to false. Then, the object is still on the display list, but AIR for TV does not render or display it. This technique is useful for objects that frequently come and go from view, because it incurs only a little processing overhead. However, setting the visible property to false does not release any of the object’s resources. Therefore, when you are done displaying an object, or at least done with it for a long time, remove the object from the display list. Also, set all references to the object to null. These actions allow the garbage collector to release the object’s resources.

PNG and JPEG image usage

Two common image formats in applications are PNG and JPEG. Regarding these image formats in AIR for TV applications, consider the following:

  • AIR for TV typically uses hardware acceleration to decode JPEG files.

  • AIR for TV typically uses software to decode PNG files. Decoding PNG files in software is fast.

  • PNG is the only cross-platform bitmap format that supports transparency (an alpha channel).

Therefore, use these image formats as follows in your applications:

  • Use JPEG files for photographs to benefit from the hardware accelerated decoding.

  • Use PNG image files for user interface elements. The user interface elements can have an alpha setting, and the software decoding provides fast enough performance for user interface elements.

The stage in AIR for TV applications

When authoring an AIR for TV application, consider the following when working with the Stage class:

  • Screen resolution

  • The safe viewing area

  • The stage scale mode

  • The stage alignment

  • The stage display state

  • Designing for multiple screen sizes

  • The stage quality setting

Screen resolution

Currently, TV devices typically have one of these screen resolutions: 540p, 720p, and 1080p. These screen resolutions result in the following values in the ActionScript Capabilities class:

Screen resolution

Capabilities.screenResolutionX

Capabilities.screenResolutionY

540p

960

540

720p

1280

720

1080p

1920

1080

To write a full-screen AIR for TV application for a specific device, hard code Stage.stageWidth and Stage.stageHeight to the device’s screen resolution. However, to write a full-screen application that runs on multiple devices, use the Capabilities.screenResolutionX and Capabilities.screenResolutionY properties to set your Stage dimensions.

For example:

stage.stageWidth = Capabilities.screenResolutionX; 
stage.stageHeight = Capabilities.screenResolutionY;

The safe viewing area

The safe viewing area on a television is an area of the screen that is inset from the screen’s edges. This area is inset far enough that the end user can see the entire area, without the TV’s bezel obscuring any part of the area. Because the bezel, which is the physical frame around the screen, varies among manufacturers, the necessary inset varies. The safe viewing area attempts to guarantee the area of the screen that is visible. The safe viewing area is also known as the title safe area.

Overscan is the area of the screen that is not visible because it is behind the bezel.

Adobe recommends an inset of 7.5% on each edge of the screen. For example:

View full size graphic
Safe viewing area for a screen resolution of 1920 x 1080

Always consider the safe viewing area when designing a full-screen AIR for TV application:

  • Use the entire screen for backgrounds, such as background images or background colors.

  • Use only the safe viewing area for critical application elements such as text, graphics, video, and user interface items such as buttons.

The following table shows the dimensions of the safe viewing area for each of the typical screen resolutions, using an inset of 7.5%.

Screen resolution

Width and height of safe viewing area

Left and right inset width

Top and bottom inset height

960 x 540

816 x 460

72

40

1280 x 720

1088 x 612

96

54

1920 x 1080

1632 x 918

144

81

However, a best practice is to always dynamically calculate the safe viewing area. For example:

var horizontalInset, verticalInset, safeAreaWidth, safeAreaHeight:int; 
 
horizontalInset = .075 * Capabilities.screenResolutionX; 
verticalInset = .075 * Capabilities.screenResolutionY; 
safeAreaWidth = Capabilities.screenResolutionX - (2 * horizontalInset); 
safeAreaHeight = Capabilities.screenResolutionY - (2 * verticalInset);

Stage scale mode

Set Stage.scaleMode to StageScaleMode.NO_SCALE, and listen for stage resize events.

stage.scaleMode = StageScaleMode.NO_SCALE; 
stage.addEventListener(Event.RESIZE, layoutHandler);

This setting makes stage coordinates the same as pixel coordinates. Along with FULL_SCREEN_INTERACTIVE display state and the TOP_LEFT stage alignment, this setting allows you to effectively use the safe viewing area.

Specifically, in full-screen applications, this scale mode means that the stageWidth and stageHeight properties of the Stage class correspond to the screenResolutionX and screenResolutionY properties of the Capabilities class.

Furthermore, when the application’s window changes size, the stage contents maintain their defined size. The runtime performs no automatic layout or scaling. Also, the runtime dispatches the Stage class’s resize event when the window changes size. Therefore, you have full control over how to adjust the application’s contents when the application begins and when the application window resizes.

Note: The NO_SCALE behavior is the same as with any AIR application. In AIR for TV applications, however, using this setting is critical to using the safe viewing area.

Stage alignment

Set Stage.align to StageAlign.TOP_LEFT:

stage.align = StageAlign.TOP_LEFT; 

This alignment places the 0,0 coordinate in the upper-left corner of the screen, which is convenient for content placement using ActionScript.

Along with the NO_SCALE scale mode and the FULL_SCREEN_INTERACTIVE display state, this setting allows you to effectively use the safe viewing area.

Stage display state

Set Stage.displayState in a full-screen AIR for TV application to StageDisplayState.FULL_SCREEN_INTERACTIVE:

stage.displayState = StageDisplayState.FULL_SCREEN_INTERACTIVE; 

This value sets the AIR application to expand the stage over the entire screen, with user input allowed.

Adobe recommends that you use the FULL_SCREEN_INTERACTIVE setting. Along with the NO_SCALE scale mode and the TOP_LEFT stage alignment, this setting allows you to effectively use the safe viewing area.

Therefore, for full screen applications, in a handler for the ADDED_TO_STAGE event on the main document class, do the following:

private function onStage(evt:Event):void 
{ 
    stage.scaleMode = StageScaleMode.NO_SCALE; 
    stage.align = StageAlign.TOP_LEFT; 
    stage.addEventListener(Event.RESIZE, onResize); 
    stage.displayState = StageDisplayState.FULL_SCREEN_INTERACTIVE; 
}

Then, in the handler for the RESIZE event:

  • Compare the screen resolution sizes with the stage width and height. If they are the same, the RESIZE event occurred because the stage display state changed to FULL_SCREEN_INTERACTIVE.

  • Calculate and save the dimensions of the safe viewing area and corresponding insets.

private function onResize(evt:Event):void 
{ 
    if ((Capabilities.screenResolutionX == stage.stageWidth) && 
        (Capabilities.screenResolutionY == stage.stageHeight)) 
    { 
         
        // Calculate and save safe viewing area dimensions. 
    } 
}

When the stage dimensions equal Capabilities.screenResolutionX and screenResolutionY, AIR for TV causes the hardware to deliver the best possible fidelity for your video and graphics.

Note: The fidelity at which graphics and video are displayed on a TV screen can differ from the Capabilities.screenResolutionX and screenResolutionY values, which depend on the device running AIR for TV. For example, a set-top box running AIR for TV can have a screen resolution of 1280 x 720 and the connected TV can have a screen resolution of 1920 x 1080. However, AIR for TV causes the hardware to deliver the best possible fidelity. Therefore, in this example, the hardware displays a 1080p video using a 1920 x 1080 screen resolution.

Designing for multiple screen sizes

You can develop the same full-screen AIR for TV application to work and look good on multiple AIR for TV devices. Do the following:

  1. Set the stage properties scaleMode, align, and displayState to the recommended values: StageScaleMode.NO_SCALE, StageAlign.TOP_LEFT, and StageDisplayState.FULL_SCREEN_INTERACTIVE, respectively.

  2. Set up the safe viewing area based on Capabilities.screenResolutionX and Capabilities.screenResolutionY.

  3. Adjust the size and layout of your content according to width and height of the safe viewing area.

    Although your content’s objects are large, especially compared to mobile device applications, concepts such as dynamic layout, relative positioning, and adaptive content are the same. For further information about ActionScript to support these concepts, see Authoring mobile Flash content for multiple screen sizes.

Stage quality

The Stage.quality property for an AIR for TV application is always StageQuality.High. You cannot change it.

This property specifies the rendering quality for all Stage objects.

Remote control input handling

Users typically interact with your AIR for TV application using a remote control. However, handle key input the same way you handle key input from a keyboard on a desktop application. Specifically, handle the event KeyboardEvent.KEY_DOWN. For more information, see Capturing keyboard input in the ActionScript 3.0 Developer’s Guide.

The keys on the remote control map to ActionScript constants. For example, the keys on the directional keypad on a remote control map as follows:

Remote control’s directional keypad key

ActionScript 3.0 constant

Up

Keyboard.UP

Down

Keyboard.DOWN

Left

Keyboard.LEFT

Right

Keyboard.RIGHT

OK or Select

Keyboard.ENTER

AIR 2.5 added many other Keyboard constants to support remote control input. For a complete list, see the Keyboard class in the ActionScript 3.0 Reference for the Adobe Flash Platform.

To ensure your application works on as many devices as possible, Adobe recommends the following:

  • Use only the directional keypad keys, if possible.

    Different remote control devices have different sets of keys. However, they typically always have the directional keypad keys.

    For example, a remote control for a Blu-ray player does not typically have a “channel up” and “channel down” key. Even keys for play, pause, and stop are not on all remote controls.

  • Use the Menu and Info keys if the application needs more than the directional keypad keys.

    The Menu and Info keys are the next most common keys on remote controls.

  • Consider the frequent usage of universal remote controls.

    Even if you are creating an application for a particular device, realize that many users do not use the remote control that comes with the device. Instead, they use a universal remote control. Also, users do not always program their universal remote control to match all the keys on the device’s remote control. Therefore, using only the most common keys is advisable.

  • Make sure that the user can always escape a situation using one of the directional keypad keys.

    Sometimes your application has a good reason to use a key that is not one of the most common keys on remote controls. Providing an escape route with one of the directional keypad keys makes your application behave gracefully on all devices.

  • Do not require pointer input unless you know the target AIR for TV device has a pointer input capability.

    Although many desktop applications expect mouse input, most televisions do not support pointer input. Therefore, if you are converting desktop applications to run on televisions, make sure that you modify the application to not expect mouse input. These modifications include changes to event handling and changes to instructions to the user. For example, when an application’s startup screen displays, do not display text that says “Click to start”.

Managing focus

When a user interface element has the focus in a desktop application, it is the target of user input events such as keyboard and mouse events. Furthermore, an application highlights the user interface element with the focus. Managing focus in an AIR for TV application is different from managing focus in a desktop application because:

  • Desktop applications often use the tab key to change focus to the next user interface element. Using the tab key doesn’t apply to AIR for TV applications. Remote control devices do not typically have a tab key. Therefore, managing focus with the tabEnabled property of a DisplayObject like on the desktop does not apply.

  • Desktop applications often expect the user to use the mouse to give focus to a user interface element.

Therefore, in your application, do the following:

  • Add an event listener to the Stage that listens for Keyboard events such as KeyboardEvent.KEY_DOWN.

  • Provide application logic to determine which user interface element to highlight to the end user. Be sure to highlight a user interface element when the application starts.

  • Based on your application logic, dispatch the Keyboard event that the Stage received to the appropriate user interface element object.

    You can also use Stage.focus or Stage.assignFocus() to assign the focus to a user interface element. You can then add an event listener to that DisplayObject so that it receives keyboard events.

User interface design

Make the user interface of an AIR for TV application work well on televisions by incorporating these recommendations regarding:

  • the application’s responsiveness

  • the application’s usability

  • the user’s personality and expectations

Responsiveness

Use the following tips to make an AIR for TV application as responsive as possible.

  • Make the application’s initial SWF file as small as possible.

    In the initial SWF file, load only the necessary resources to start the application. For example, load only the application’s startup screen image.

    Although this recommendation is valid for desktop AIR applications, it is more important on AIR for TV devices. For example, AIR for TV devices do not have the equivalent processing power of desktop computers. Also, they store the application in flash memory, which is not as fast to access as hard disks on desktop computers.

  • Make the application run at a frame rate of at least 20 frames per second.

    Design your graphics to achieve this goal. The complexity of your graphics operations can affect your frames per second. For tips on improving rendering performance, see Optimizing Performance for the Adobe Flash Platform.

    Note: The graphics hardware on AIR for TV devices typically updates the screen at a rate of 60 Hz or 120 Hz (60 or 120 times per second). The hardware scans the stage for updates at, for example, 30 frames per second or 60 frames per second for display on the 60-Hz or 120-Hz screen. However, whether the user experiences these higher frame rates depends on the complexity of the application’s graphics operations.
  • Update the screen within 100 - 200 milliseconds of user input.

    Users become impatient if updates take longer, often resulting in multiple keypresses.

Usability

Users of AIR for TV applications are in a “living room” environment. They are sitting across the room from the TV, some 10 feet away. The room is sometimes dark. They typically use a remote control device for input. More than one person can be using the application, sometimes together, sometimes serially.

Therefore, to design your user interface for usability on a TV, consider the following:

  • Make the user interface elements large.

    When designing text, buttons, or any other user interface elements, consider that the user is sitting across the room. Make everything easy to see and read from, for example, 10 feet away. Do not be tempted to crowd the screen just because the screen is large.

  • Use good contrast to make the content easy to see and read from across the room.

  • Make obvious which user interface element has the focus by making that element bright.

  • Use motion only as necessary. For example, sliding from one screen to the next for continuity can work well. However, motion can be distracting if it does not help the user navigate or if it is not intrinsic to the application.

  • Always provide an obvious way for the user to go back through the user interface.

For more information about using the remote control, see Remote control input handling.

User’s personality and expectations

Consider that users of AIR for TV applications are typically seeking TV quality entertainment in a fun and relaxed environment. They are not necessarily knowledgeable about computers or technology.

Therefore, design AIR for TV applications with the following characteristics:

  • Do not use technical terms.

  • Avoid modal dialogs.

  • Use friendly, informal instructions appropriate for a living room environment, not for a work or technical environment.

  • Use graphics that have the high production quality that TV watchers expect.

  • Create a user interface that works easily with a remote control device. Do not use user interface or design elements that are better suited to a desktop or mobile application. For example, user interfaces on desktop and mobile devices often involve pointing and clicking buttons with a mouse or a finger.

Fonts and text

You can use either device fonts or embedded fonts in your AIR for TV application.

Device fonts are fonts that are installed on a device. All AIR for TV devices have the following device fonts:

Font name

Description

_sans

The _sans device font is a sans-serif typeface. The _sans device font. installed on all AIR for TV devices is Myriad Pro. Typically, a sans-serif typeface looks better on a TV than serif typefaces, because of the viewing distance.

_serif

The _serif device font is a serif typeface. The _serif device font installed on all AIR for TV devices is Minion Pro.

_typewriter

The _typewriter device font is a monospace font. The _typewriter device font installed on all AIR for TV devices is Courier Std.

All AIR for TV devices also have the following Asian device fonts:

Font name

Language

Typeface category

locale code

RyoGothicPlusN-Regular

Japanese

sans

ja

RyoTextPlusN-Regular

Japanese

serif

ja

AdobeGothicStd-Light

Korean

sans

ko

AdobeHeitiStd-Regular

Simplified Chinese

sans

zh_CN

AdobeSongStd-Light

Simplified Chinese

serif

zh_CN

AdobeMingStd-Light

Traditional Chinese

serif

zh_TW and zh_HK

These AIR for TV device fonts are:

  • From the Adobe® Type Library

  • Look good on televisions

  • Designed for video titling

  • Are font outlines, not bitmap fonts

Note: Device manufacturers often include other device fonts on the device. These manufacturer-provided device fonts are installed in addition to the AIR for TV device fonts.

Adobe provides an application called FontMaster Deluxe that displays all the device fonts on the device. The application is available at Flash Platform for TV.

You can also embed fonts in your AIR for TV application. For information on embedded fonts, see Advanced text rendering in the ActionScript 3.0 Developer’s Guide.

Adobe recommends the following regarding using TLF text fields:

  • Use TLF text fields for Asian language text to take advantage of the locale in which the application is running. Set the locale property of the TextLayoutFormat object associated with the TLFTextField object. To determine the current locale, see Choosing a locale in the ActionScript 3.0 Developer’s Guide.

  • Specify the font name in the fontFamily property in the TextLayoutFormat object if the font is not one of the AIR for TV device fonts. AIR for TV uses the font if it is available on the device. If the font you request is not on the device, based on the locale setting, AIR for TV substitutes the appropriate AIR for TV device font.

  • Specify _sans, _serif, or _typewriter for the fontFamily property, along with setting the locale property, to cause AIR for TV to choose the correct AIR for TV device font. Depending on the locale, AIR for TV chooses from its set of Asian device fonts or its set of non-Asian device fonts. These settings provide an easy way for you to automatically use the correct font for the four major Asian locales and English.

Note: If you use classic text fields for Asian language text, specify a font name of an AIR for TV device font to guarantee proper rendering. If you know that another font is installed on your target device, you can also specify it.

Regarding application performance, consider the following:

  • Classic text fields provide faster performance than TLF text fields.

  • A classic text field that uses bitmap fonts provides the fastest performance.

    Bitmap fonts provide a bitmap for each character, unlike outline fonts, which provide only outline data about each character. Both device fonts and embedded fonts can be bitmap fonts.

  • If you specify a device font, make sure that the device font is installed on your target device. If it is not installed on the device, AIR for TV finds and uses another font that is installed on the device. However, this behavior slows the application’s performance.

  • As with any display object, if a TextField object is mostly unchanging, set the object’s cacheAsBitmap property to true. This setting improves performance for transitions such as fading, sliding, and alpha blending. Use cacheAsBitmapMatrix for scaling and translation. For more information, see Graphics hardware acceleration.

File system security

AIR for TV applications are AIR applications, and, therefore, can access the device’s filesystem. However, on a “living room” device it is critically important that an application cannot access the device’s system files or the files of other applications. Users of TVs and associated devices do not expect or tolerate any device failures — they are watching TV, after all.

Therefore, an AIR for TV application has a limited view of the device’s filesystem. Using ActionScript 3.0, your application can access only specific directories (and their subdirectories). Furthermore, the directory names that you use in ActionScript are not the actual directory names on the device. This extra layer protects AIR for TV applications from maliciously or inadvertently accessing local files that do not belong to them.

For details, see Directory view for AIR for TV applications.

The AIR application sandbox

AIR for TV applications run in the AIR application sandbox, described in The AIR application sandbox.

The only difference for AIR for TV applications is that they have limited access to the file system as described in File system security.

Application life cycle

Unlike on a desktop environment, the end user cannot close the window in which your AIR for TV application is running. Therefore, provide a user interface mechanism for exiting the application.

Typically, a device allows the end user to unconditionally exit an application with the exit key on the remote control. However, AIR for TV does not dispatch the event flash.events.Event.EXITING to the application. Therefore, save the application state frequently so that the application can restore itself to a reasonable state when it next starts.

HTTP cookies

AIR for TV supports HTTP persistent cookies and session cookies. AIR for TV stores each AIR application’s cookies in an application-specific directory:

/app-storage/<app id>/Local Store

The cookie file is named cookies.

Note: AIR on other devices, such as desktop devices, does not store cookies separately for each application. Application-specific cookie storage supports the application and system security model of AIR for TV.

Use the ActionScript property URLRequest.manageCookies as follows:

  • Set manageCookies to true. This value is the default. It means that AIR for TV automatically adds cookies to HTTP requests and remembers cookies in the HTTP response.

    Note: Even when manageCookies is true, the application can manually add a cookie to an HTTP request using URLRequest.requestHeaders. If this cookie has the same name as a cookie that AIR for TV is managing, the request contains two cookies with the same name. The values of the two cookies can be different.
  • Set manageCookies to false. This value means that the application is responsible for sending cookies in HTTP requests, and for remembering the cookies in the HTTP response.

For more information, see URLRequest.