VideoModule.java

@Override
public void onCameraAvailable(CameraProxy cameraProxy) {
    ...
    startPreview(true);
    ...
}

startPreview() 与 PhotoModule 基本一致，不做详解

开始录像

private void startVideoRecording() {
    //更新 UI，判断存储是否低于设定的阈值
    ...

    // 初始化 MediaRecorder
    initializeRecorder();
    ...
                    
    try {
        // 调用 requestAudioFocus 获取 STREAM_MUSIC 焦点，暂停正在播放的音频
        // 调用 setRingerMode 设置情景模式为 RINGER_MODE_SILENT，保证录像期间没有声音和震动提示
        ...
        // 启动录像
        mMediaRecorder.start(); 
    } catch (IllegalStateException exception) {
        // 实现同 catch (RuntimeException e){}
        return;
    } catch (RuntimeException e) {
        // Could not start media recorder(start failed)
        ...
        // releasing media recorder
        if (mMediaRecorder != null) {
            mMediaRecorder.reset();
            mMediaRecorder.release();
            mMediaRecorder = null;
        }
        // 调用 setRingerMode 恢复原有情景模式
        if (mAudioManager.getRingerMode() == AudioManager.RINGER_MODE_SILENT) {
            mAudioManager.setRingerMode(mOriginalRingerMode);
        }
        // If start fails, frameworks will not lock the camera for us.
        mCameraDevice.lock();
        return;
    }
    ...
}

    private MediaRecorder mMediaRecorder;
    private static Class<?> mediaRecoderExClazz = null;
    private static Class<?> mediaRecoderClazz = null;

    private static boolean OLD_SDK_VERSION = 
            Build.VERSION.SDK_INT <= Build.VERSION_CODES.M ? true : false;
    static {
        try {
            mediaRecoderClazz = Class.forName("android.media.MediaRecorder");
            mediaRecoderExClazz = Class.forName("android.media.MediaRecorderEx");
        } catch (Exception e) {
            // get class of MediaRecorder or MediaRecorderEx error
        }

    }
    // Prepares media recorder.
    private void initializeRecorder() {
        ...
        // 初始化 MediaRecorder 对象
        try {
            if (OLD_SDK_VERSION) {
                mMediaRecorder = mediaRecoderClazz.newInstance();
            } else {
                mMediaRecorder = mediaRecoderExClazz.newInstance();
            }
            return mMediaRecorder;
        } catch (Exception e) {
            return null;
        }

        // *必要* 解锁 Camera，使得 MediaRecorder 进程能访问 Camera 硬件
        mCameraDevice.unlock();
        
        // We rely here on the fact that the unlock call above is synchronous
        // and blocks until it occurs in the handler thread. Thereby ensuring
        // that we are up to date with handler requests, and if this proxy had
        // ever been released by a prior command, it would be null.
        Camera camera = mCameraDevice.getCamera();
        // If the camera device is null, the camera proxy is stale and recording
        // should be ignored.
        if (camera == null) {
            Log.w(TAG, "null camera within proxy, not recording");
            return;
        }

        // *必要* 设置 Camera 用于录像
        mMediaRecorder.setCamera(camera);

        ...

        Method method;
        try {
            if (mMediaRecorder != null) {
                if (OLD_SDK_VERSION) {
                    method = mediaRecoderClazz.getMethod(
                            "setParam64BitFileOffset", boolean.class);
                    method.invoke(mMediaRecorder, use64BitFlag);
                } else {
                    method = mediaRecoderExClazz.getMethod(
                            "setParam64BitFileOffset", boolean.class);
                    method.invoke(mMediaRecorder, use64BitFlag);
                }
            }
        } catch (Exception e) {
            // setParam64BitFileOffset error
        }

        // *必要* 设置录像音频来源, 使用麦克风 MediaRecorder.AudioSource.CAMCORDER 作为音频来源
        mMediaRecorder.setAudioSource(MediaRecorder.AudioSource.CAMCORDER);
       
        // *必要* 设置录像视频来源, 使用Camera MediaRecorder.VideoSource.CAMERA 作为视频来源
        mMediaRecorder.setVideoSource(MediaRecorder.VideoSource.CAMERA);

        mMediaRecorder.setProfile(mProfile);
        
        // 设置视频尺寸大小，在 setVideoSource() 和 setOutFormat() 之后 prepare() 之前调用
        mMediaRecorder.setVideoSize(mProfile.videoFrameWidth,
                mProfile.videoFrameHeight);
        
        // 设置录制会话的最长持续时间(以ms为单位)
        mMediaRecorder.setMaxDuration(mMaxVideoDurationInMs);
        
        // 设置视频帧捕获率
        mMediaRecorder.setCaptureRate(fps);

        Location loc = mLocationManager.getCurrentLocation();
        if (loc != null) {
            // 设置并存储在输出文件中的地理数据(经度和纬度)
            mMediaRecorder.setLocation((float) loc.getLatitude(),
                    (float) loc.getLongitude());
        }

        // *必要* 设置视频输出文件的路径
        mMediaRecorder.setOutputFile(mVideoFilename);

        // Set maximum file size.
        try {
            // 设置录制文件的最大文件大小
            mMediaRecorder.setMaxFileSize(maxFileSize);
        } catch (RuntimeException exception) {
            // We are going to ignore failure of setMaxFileSize here, as
            // a) The composer selected may simply not support it, or
            // b) The underlying media framework may not handle 64-bit range
            // on the size restriction.
        }

        // 输出旋转90度，保持竖屏录制
        mMediaRecorder.setOrientationHint(90);

        try {
            // *必要* 准备录制
            mMediaRecorder.prepare();
        } catch (IOException e) {
            // prepare failed
            // releasing media recorder
            if (mMediaRecorder != null) {
                mMediaRecorder.reset();
                mMediaRecorder.release();
                mMediaRecorder = null;
            }
            throw new RuntimeException(e);
        }

        // 注册一个用于记录录制时出现错误的监听器
        mMediaRecorder.setOnErrorListener(this);
        
        // 注册一个用于记录录制时出现的信息事件的监听器
        mMediaRecorder.setOnInfoListener(this);
    }

停止录像

    private boolean stopVideoRecording(boolean shouldSaveVideo, boolean checkStorage) {
        ...

        boolean fail = false;

        try {
            mMediaRecorder.setOnErrorListener(null);
            mMediaRecorder.setOnInfoListener(null);

            // *必要* 停止录制
            mMediaRecorder.stop();
            ...
        } catch (RuntimeException e) {
            // stop fail delete Video File
            if (mVideoFilename != null) {
                deleteVideoFile(mVideoFilename);
            }
            fail = true;
        }

        ...

        // 保存录像
        saveVideo();

        if (mMediaRecorder != null) {
            /**
             * 必要
             * 重置多媒体状态，调用该方法之后之前的所有 MediaRecorder configuration 将被移除
             * 如果还想再次录像，需要再次配置  MediaRecorder configuration
             */
            mMediaRecorder.reset();
            // *必要* 释放多媒体资源
            mMediaRecorder.release();
            mMediaRecorder = null;
        }
        ...

        // *必要* 给 Camera 硬件加锁
        mCameraDevice.lock();

        ...

        return fail;
    }