Android 音視頻開發 - VideoView

本篇文章主要介紹下Android 中的VideoView.

1: VideoView簡介

VideoView是一個用於播放視頻的視圖組件，可以方便地在應用程式中播放本地或網路上的視頻文件。

VideoView可以直接在佈局文件中使用，也可以在代碼中動態創建。

它封裝了MediaPlayer和SurfaceView，提供了簡單的介面來控制視頻的播放和顯示。

它提供了一系列方法來控制視頻的播放、暫停、停止等操作，並且支持全屏播放和視頻控制器的顯示。

VideoView播放視頻非常簡單，只需要指定視頻的URL或本地路徑.

2: 使用

以下是VideoView的簡單使用:

2.1 佈局

在XML佈局文件中添加VideoView組件.

<VideoView
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    android:id="@+id/videoview"
    />

2.2 設置視頻源

代碼如下:

videoView = findViewById(R.id.videoview);
videoView.setVideoPath("sdcard/test.mp4");

除了setVideoPath外,我們還可以調用:

1. setVideoURI(Uri uri)
2. setVideoURI(Uri uri, Map<String, String> headers)

當然不管是setVideoPath或者setVideoURI實際都是執行的setVideoURI(Uri uri, Map<String, String> headers).

源碼如下:

/**
 * Sets video path.
 *
 * @param path the path of the video.
 */
public void setVideoPath(String path) {
    setVideoURI(Uri.parse(path));
}

/**
 * Sets video URI.
 *
 * @param uri the URI of the video.
 */
public void setVideoURI(Uri uri) {
    setVideoURI(uri, null);
}

2.3 播放視頻

videoView.start();

我們可以看下start()的源碼:

@Override
public void start() {
    if (isInPlaybackState()) {
        mMediaPlayer.start();
        mCurrentState = STATE_PLAYING;
    }
    mTargetState = STATE_PLAYING;
}

可以看到實際上調用mMediaPlayer.start();另外設置了當前的狀態為STATE_PLAYING.

這裡直接調用了mMediaPlayer.start();那mMediaPlayer是什麼時機初始化的呢?

查看源碼可以看到:

private void openVideo() {
    if (mUri == null || mSurfaceHolder == null) {
        // not ready for playback just yet, will try again later
        return;
    }
    // we shouldn't clear the target state, because somebody might have
    // called start() previously
    release(false);

    if (mAudioFocusType != AudioManager.AUDIOFOCUS_NONE) {
        // TODO this should have a focus listener
        mAudioManager.requestAudioFocus(null, mAudioAttributes, mAudioFocusType, 0 /*flags*/);
    }

    try {
        mMediaPlayer = new MediaPlayer();
        // TODO: create SubtitleController in MediaPlayer, but we need
        // a context for the subtitle renderers
        final Context context = getContext();
        final SubtitleController controller = new SubtitleController(
                context, mMediaPlayer.getMediaTimeProvider(), mMediaPlayer);
        controller.registerRenderer(new WebVttRenderer(context));
        controller.registerRenderer(new TtmlRenderer(context));
        controller.registerRenderer(new Cea708CaptionRenderer(context));
        controller.registerRenderer(new ClosedCaptionRenderer(context));
        mMediaPlayer.setSubtitleAnchor(controller, this);

        if (mAudioSession != 0) {
            mMediaPlayer.setAudioSessionId(mAudioSession);
        } else {
            mAudioSession = mMediaPlayer.getAudioSessionId();
        }
        mMediaPlayer.setOnPreparedListener(mPreparedListener);
        mMediaPlayer.setOnVideoSizeChangedListener(mSizeChangedListener);
        mMediaPlayer.setOnCompletionListener(mCompletionListener);
        mMediaPlayer.setOnErrorListener(mErrorListener);
        mMediaPlayer.setOnInfoListener(mInfoListener);
        mMediaPlayer.setOnBufferingUpdateListener(mBufferingUpdateListener);
        mCurrentBufferPercentage = 0;
        mMediaPlayer.setDataSource(mContext, mUri, mHeaders);
        mMediaPlayer.setDisplay(mSurfaceHolder);
        mMediaPlayer.setAudioAttributes(mAudioAttributes);
        mMediaPlayer.setScreenOnWhilePlaying(true);
        mMediaPlayer.prepareAsync();

        for (Pair<InputStream, MediaFormat> pending: mPendingSubtitleTracks) {
            try {
                mMediaPlayer.addSubtitleSource(pending.first, pending.second);
            } catch (IllegalStateException e) {
                mInfoListener.onInfo(
                        mMediaPlayer, MediaPlayer.MEDIA_INFO_UNSUPPORTED_SUBTITLE, 0);
            }
        }

        // we don't set the target state here either, but preserve the
        // target state that was there before.
        mCurrentState = STATE_PREPARING;
        attachMediaController();
    } catch (IOException ex) {
        Log.w(TAG, "Unable to open content: " + mUri, ex);
        mCurrentState = STATE_ERROR;
        mTargetState = STATE_ERROR;
        mErrorListener.onError(mMediaPlayer, MediaPlayer.MEDIA_ERROR_UNKNOWN, 0);
        return;
    } catch (IllegalArgumentException ex) {
        Log.w(TAG, "Unable to open content: " + mUri, ex);
        mCurrentState = STATE_ERROR;
        mTargetState = STATE_ERROR;
        mErrorListener.onError(mMediaPlayer, MediaPlayer.MEDIA_ERROR_UNKNOWN, 0);
        return;
    } finally {
        mPendingSubtitleTracks.clear();
    }
}

可以看到openVideo()

1. release()方法釋放正在播放的視頻.
2. 初始化mMediaPlayer,傳入Uri,設置狀態 STATE_PREPARING。
3. attachMediaController()綁定MediaPlayer與VideoView。

最後openVideo()則是在setVideoURI(Uri uri, Map<String, String> headers)內調用。

這樣其實已經可以播放指定的視頻了。

下麵的方法可選。

2.4 MediaController控制器

MediaController是一個用於控制媒體播放器的視圖組件。

MediaController的使用步驟如下：

1. 創建一個MediaController對象：MediaController mediaController = new MediaController(context);
2. 將MediaController與媒體播放器組件關聯：mediaController.setMediaPlayer(mediaPlayer);
3. 將MediaController添加到佈局中：layout.addView(mediaController);

videoView.setMediaController(new MediaController(this));
videoView.start().

直接調用setMediaController,運行後我們可以看到與之前直接調用start()的區別就是多了個控制器的顯示。其中包含一組常用的媒體控制按鈕，如播放/暫停、快進/快退、前進/後退等，並且可以與MediaPlayer或VideoView等媒體播放器組件進行關聯.

我們可以看下源碼：

public void setMediaController(MediaController controller) {
    if (mMediaController != null) {
        mMediaController.hide();
    }
    mMediaController = controller;
    attachMediaController();
}

可以看到做的操作如下：

1. 如果存在mMediaController，則調用hide方法。
2. 對mMediaController賦值
3. attachMediaController

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