管理 TV 用户交互

在直播电视体验中，用户切换频道，会短暂显示频道和节目信息，然后信息消失。其他类型的信息，例如消息（“不要在家尝试”）、字幕或广告可能需要持续显示。与任何电视应用一样，此类信息不应干扰屏幕上播放的节目内容。

图 1. 直播电视应用中的叠加消息。

还要考虑是否应呈现某些节目内容，以及如何根据内容的评级和家长控制设置以及应用的行为以及在内容被屏蔽或不可用时如何通知用户。本课程介绍如何针对这些考虑因素为您的电视输入开发用户体验。

试用 TV 输入服务 示例应用。

将播放器与表面集成

您的电视输入必须将视频渲染到 Surface 对象上，该对象由 TvInputService.Session.onSetSurface() 方法传递。以下是如何在 Surface 对象中使用 MediaPlayer 实例播放内容的示例

Kotlin

override fun onSetSurface(surface: Surface?): Boolean {
    player?.setSurface(surface)
    mSurface = surface
    return true
}

override fun onSetStreamVolume(volume: Float) {
    player?.setVolume(volume, volume)
    mVolume = volume
}

Java

@Override
public boolean onSetSurface(Surface surface) {
    if (player != null) {
        player.setSurface(surface);
    }
    mSurface = surface;
    return true;
}

@Override
public void onSetStreamVolume(float volume) {
    if (player != null) {
        player.setVolume(volume, volume);
    }
    mVolume = volume;
}

同样，以下是如何使用 ExoPlayer 执行此操作

Kotlin

override fun onSetSurface(surface: Surface?): Boolean {
    player?.createMessage(videoRenderer)?.apply {
        type = MSG_SET_SURFACE
        payload = surface
        send()
    }
    mSurface = surface
    return true
}

override fun onSetStreamVolume(volume: Float) {
    player?.createMessage(audioRenderer)?.apply {
        type = MSG_SET_VOLUME
        payload = volume
        send()
    }
    mVolume = volume
}

Java

@Override
public boolean onSetSurface(@Nullable Surface surface) {
    if (player != null) {
        player.createMessage(videoRenderer)
                .setType(MSG_SET_SURFACE)
                .setPayload(surface)
                .send();
    }
    mSurface = surface;
    return true;
}

@Override
public void onSetStreamVolume(float volume) {
    if (player != null) {
        player.createMessage(videoRenderer)
                .setType(MSG_SET_VOLUME)
                .setPayload(volume)
                .send();
    }
    mVolume = volume;
}

使用叠加层

使用叠加层显示字幕、消息、广告或 MHEG-5 数据广播。默认情况下，叠加层处于禁用状态。您可以在创建会话时通过调用 TvInputService.Session.setOverlayViewEnabled(true) 来启用它，如下面的示例所示

Kotlin

override fun onCreateSession(inputId: String): Session =
        onCreateSessionInternal(inputId).apply {
            setOverlayViewEnabled(true)
            sessions.add(this)
        }

Java

@Override
public final Session onCreateSession(String inputId) {
    BaseTvInputSessionImpl session = onCreateSessionInternal(inputId);
    session.setOverlayViewEnabled(true);
    sessions.add(session);
    return session;
}

对于叠加层，使用 View 对象，该对象从 TvInputService.Session.onCreateOverlayView() 返回，如下所示

Kotlin

override fun onCreateOverlayView(): View =
        (context.getSystemService(LAYOUT_INFLATER_SERVICE) as LayoutInflater).run {
            inflate(R.layout.overlayview, null).apply {
                subtitleView = findViewById<SubtitleView>(R.id.subtitles).apply {
                    // Configure the subtitle view.
                    val captionStyle: CaptionStyleCompat =
                            CaptionStyleCompat.createFromCaptionStyle(captioningManager.userStyle)
                    setStyle(captionStyle)
                    setFractionalTextSize(captioningManager.fontScale)
                }
            }
        }

Java

@Override
public View onCreateOverlayView() {
    LayoutInflater inflater = (LayoutInflater) getSystemService(LAYOUT_INFLATER_SERVICE);
    View view = inflater.inflate(R.layout.overlayview, null);
    subtitleView = (SubtitleView) view.findViewById(R.id.subtitles);

    // Configure the subtitle view.
    CaptionStyleCompat captionStyle;
    captionStyle = CaptionStyleCompat.createFromCaptionStyle(
            captioningManager.getUserStyle());
    subtitleView.setStyle(captionStyle);
    subtitleView.setFractionalTextSize(captioningManager.fontScale);
    return view;
}

叠加层的布局定义可能如下所示

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"

    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <com.google.android.exoplayer.text.SubtitleView
        android:id="@+id/subtitles"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom|center_horizontal"
        android:layout_marginLeft="16dp"
        android:layout_marginRight="16dp"
        android:layout_marginBottom="32dp"
        android:visibility="invisible"/>
</FrameLayout>

控制内容

当用户选择频道时，您的电视输入会在 TvInputService.Session 对象中处理 onTune() 回调。系统电视应用的家长控制会根据内容评级确定显示的内容。以下部分介绍了如何使用与系统电视应用通信的 TvInputService.Session notify 方法管理频道和节目选择。

使视频不可用

当用户更改频道时，您需要确保屏幕在您的电视输入呈现内容之前不会显示任何杂乱的视频伪像。当您调用 TvInputService.Session.onTune() 时，您可以通过调用 TvInputService.Session.notifyVideoUnavailable() 并传递 VIDEO_UNAVAILABLE_REASON_TUNING 常量来阻止视频呈现，如下例所示。

Kotlin

override fun onTune(channelUri: Uri): Boolean {
    subtitleView?.visibility = View.INVISIBLE
    notifyVideoUnavailable(TvInputManager.VIDEO_UNAVAILABLE_REASON_TUNING)
    unblockedRatingSet.clear()

    dbHandler.apply {
        removeCallbacks(playCurrentProgramRunnable)
        playCurrentProgramRunnable = PlayCurrentProgramRunnable(channelUri)
        post(playCurrentProgramRunnable)
    }
    return true
}

Java

@Override
public boolean onTune(Uri channelUri) {
    if (subtitleView != null) {
        subtitleView.setVisibility(View.INVISIBLE);
    }
    notifyVideoUnavailable(TvInputManager.VIDEO_UNAVAILABLE_REASON_TUNING);
    unblockedRatingSet.clear();

    dbHandler.removeCallbacks(playCurrentProgramRunnable);
    playCurrentProgramRunnable = new PlayCurrentProgramRunnable(channelUri);
    dbHandler.post(playCurrentProgramRunnable);
    return true;
}

然后，当内容渲染到 Surface 时，您调用 TvInputService.Session.notifyVideoAvailable() 允许视频显示，如下所示

Kotlin

fun onRenderedFirstFrame(surface:Surface) {
    firstFrameDrawn = true
    notifyVideoAvailable()
}

Java

@Override
public void onRenderedFirstFrame(Surface surface) {
    firstFrameDrawn = true;
    notifyVideoAvailable();
}

此过渡仅持续几分之一秒，但呈现空白屏幕在视觉上比允许图片闪烁奇特的闪烁和抖动要好。

另请参见 将播放器与表面集成，以获取有关使用 Surface 渲染视频的更多信息。

提供家长控制

要确定给定内容是否被家长控制和内容评级阻止，您需要检查 TvInputManager 类方法 isParentalControlsEnabled() 和 isRatingBlocked(android.media.tv.TvContentRating)。您可能还想确保内容的 TvContentRating 包含在一组当前允许的内容评级中。以下示例中显示了这些注意事项。

Kotlin

private fun checkContentBlockNeeded() {
    currentContentRating?.also { rating ->
        if (!tvInputManager.isParentalControlsEnabled
                || !tvInputManager.isRatingBlocked(rating)
                || unblockedRatingSet.contains(rating)) {
            // Content rating is changed so we don't need to block anymore.
            // Unblock content here explicitly to resume playback.
            unblockContent(null)
            return
        }
    }
    lastBlockedRating = currentContentRating
    player?.run {
        // Children restricted content might be blocked by TV app as well,
        // but TIF should do its best not to show any single frame of blocked content.
        releasePlayer()
    }

    notifyContentBlocked(currentContentRating)
}

Java

private void checkContentBlockNeeded() {
    if (currentContentRating == null || !tvInputManager.isParentalControlsEnabled()
            || !tvInputManager.isRatingBlocked(currentContentRating)
            || unblockedRatingSet.contains(currentContentRating)) {
        // Content rating is changed so we don't need to block anymore.
        // Unblock content here explicitly to resume playback.
        unblockContent(null);
        return;
    }

    lastBlockedRating = currentContentRating;
    if (player != null) {
        // Children restricted content might be blocked by TV app as well,
        // but TIF should do its best not to show any single frame of blocked content.
        releasePlayer();
    }

    notifyContentBlocked(currentContentRating);
}

确定内容是否应该被阻止后，通过调用 TvInputService.Session 方法 notifyContentAllowed() 或 notifyContentBlocked() 通知系统电视应用程序，如前面的示例所示。

使用 TvContentRating 类使用 TvContentRating.createRating() 方法生成用于 COLUMN_CONTENT_RATING 的系统定义字符串，如下所示

Kotlin

val rating = TvContentRating.createRating(
        "com.android.tv",
        "US_TV",
        "US_TV_PG",
        "US_TV_D", "US_TV_L"
)

Java

TvContentRating rating = TvContentRating.createRating(
    "com.android.tv",
    "US_TV",
    "US_TV_PG",
    "US_TV_D", "US_TV_L");

处理音轨选择

TvTrackInfo 类包含有关媒体音轨的信息，例如音轨类型（视频、音频或字幕）等等。

您的电视输入会话首次能够获取音轨信息时，它应该使用所有音轨的列表调用 TvInputService.Session.notifyTracksChanged() 来更新系统电视应用程序。当音轨信息发生变化时，再次调用 notifyTracksChanged() 来更新系统。

系统电视应用程序为用户提供了一个界面，如果给定音轨类型存在多个音轨，则可以选择特定的音轨；例如，不同语言的字幕。您的电视输入通过调用 notifyTrackSelected() 响应来自系统电视应用程序的 onSelectTrack() 调用，如下例所示。请注意，当将 null 作为音轨 ID 传递时，这将 *取消选择* 该音轨。

Kotlin

override fun onSelectTrack(type: Int, trackId: String?): Boolean =
        mPlayer?.let { player ->
            if (type == TvTrackInfo.TYPE_SUBTITLE) {
                if (!captionEnabled && trackId != null) return false
                selectedSubtitleTrackId = trackId
                subtitleView.visibility = if (trackId == null) View.INVISIBLE else View.VISIBLE
            }
            player.trackInfo.indexOfFirst { it.trackType == type }.let { trackIndex ->
                if( trackIndex >= 0) {
                    player.selectTrack(trackIndex)
                    notifyTrackSelected(type, trackId)
                    true
                } else false
            }
        } ?: false

Java

@Override
public boolean onSelectTrack(int type, String trackId) {
    if (player != null) {
        if (type == TvTrackInfo.TYPE_SUBTITLE) {
            if (!captionEnabled && trackId != null) {
                return false;
            }
            selectedSubtitleTrackId = trackId;
            if (trackId == null) {
                subtitleView.setVisibility(View.INVISIBLE);
            }
        }
        int trackIndex = -1;
        MediaPlayer.TrackInfo[] trackInfos = player.getTrackInfo();
        for (int index = 0; index < trackInfos.length; index++) {
            MediaPlayer.TrackInfo trackInfo = trackInfos[index];
            if (trackInfo.getTrackType() == type) {
                trackIndex = index;
                break;
            }
        }
        if (trackIndex >= 0) {
            player.selectTrack(trackIndex);
            notifyTrackSelected(type, trackId);
            return true;
        }
    }
    return false;
}
上一步
使用频道数据
下一步
支持时间推移