管理电视用户交互

在直播电视体验中，用户更改频道，并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（“切勿在家尝试”）、字幕或广告可能需要持续存在。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，具体取决于内容的评级和家长控制设置，以及您的应用在内容被阻止或不可用时的行为和告知用户的方式。本课程介绍如何针对这些考虑因素开发电视输入的用户体验。

试用 电视输入服务 示例应用。

将播放器与 Surface 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;
}

类似地，以下是使用 ExoPlayer 的方法

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;
}

使用 View 对象作为叠加层，该对象由 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，您的电视输入会处理onTune()回调，该回调位于TvInputService.Session对象中。系统电视应用的家长控制功能会根据内容分级来决定显示什么内容。以下部分介绍如何使用与系统电视应用通信的TvInputService.Session notify方法来管理频道和节目选择。

使视频不可用

当用户更改频道时，您需要确保在您的电视输入渲染内容之前，屏幕不会显示任何杂散视频伪像。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常量来阻止视频显示，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()以允许显示视频，如下所示

Kotlin

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

Java

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

此转换仅持续几分之一秒，但显示空白屏幕比允许图片闪烁奇特的闪烁和抖动在视觉上更好。

另请参阅将播放器与Surface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分级阻止，您可以检查TvInputManager类的isParentalControlsEnabled()和isRatingBlocked(android.media.tv.TvContentRating)方法。您可能还需要确保内容的TvContentRating包含在一组当前允许的内容分级中。以下示例显示了这些考虑因素。

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);
}

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

使用TvContentRating类使用TvContentRating.createRating()方法生成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");

处理轨道选择

TvTrackInfo类包含有关媒体轨道的信息，例如轨道类型（视频、音频或字幕）等等。

您的电视输入会话第一次能够获取轨道信息时，应使用所有轨道的列表调用TvInputService.Session.notifyTracksChanged()来更新系统电视应用。当轨道信息发生更改时，再次调用notifyTracksChanged()来更新系统。

如果对于给定的轨道类型有多个轨道可用（例如，不同语言的字幕），则系统电视应用会为用户提供一个界面来选择特定轨道。您的电视输入通过调用notifyTrackSelected()来响应来自系统电视应用的onSelectTrack()调用，如下例所示。请注意，当传递null作为轨道 ID 时，这将取消选择轨道。

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;
}
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