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关于android:Android入门教程-Camera-相机二

jiezi

应用 Camera API 进行视频的采集，别离应用 SurfaceView、TextureView 来预览 Camera 数据，取到 NV21 的数据回调

筹备

应用相机权限 

<uses-permission android:name="android.permission.CAMERA" />

camera 预览回调中默认应用 NV21 格局。
查看手机是否反对摄像头。

UI 筹备 

<!-- 全屏显示 -->
<style name="FullScreenTheme" parent="AppTheme">
    <item name="windowNoTitle">true</item>
    <item name="android:windowFullscreen">true</item>
</style>

承载预览图像 

<FrameLayout
    android:id="@+id/camera_preview"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

应用 SurfaceView 预览 Camera，取到 NV21 数据

自定义 CameraPreview 继承 SurfaceView，实现 SurfaceHolder.Callback 接口

获取 NV21 数据，Camera.setPreviewCallback() 要放在 Camera.startPreview() 之前。应用 Camera.PreviewCallback 获取预览数据回调。默认是 NV21 格局。

surfaceChanged 中，camera 启动预览前能够进行设置，例如设置尺寸，调整方向 

/**
 * camera 预览视图
 * Created by Rust on 2018/2/26.
 */
public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback {
    private static final String TAG = "rustApp";
    private SurfaceHolder mHolder;
    private Camera mCamera;
    private int mFrameCount = 0;

    public CameraPreview(Context context) {super(context);
    }

    public CameraPreview(Context context, Camera camera) {super(context);
        mCamera = camera;
        mHolder = getHolder();
        mHolder.addCallback(this);
        mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
    }

    public void setCamera(Camera c) {this.mCamera = c;}

    @Override
    public void surfaceCreated(SurfaceHolder holder) {
        // 开启预览
        try {mCamera.setPreviewDisplay(holder);
            mCamera.startPreview();} catch (IOException e) {Log.d(TAG, "Error setting camera preview:" + e.getMessage());
        }
    }

    @Override
    public void surfaceDestroyed(SurfaceHolder holder) {// 可在此开释 camera}

    @Override
    public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
        // 若须要旋转、更改大小或从新设置，请确保障已进行预览
        if (mHolder.getSurface() == null) {return;}
        try {mCamera.stopPreview();
        } catch (Exception e) {// ignore: tried to stop a non-existent preview}
        Camera.Parameters parameters = mCamera.getParameters();
        // ImageFormat.NV21 == 17
        Log.d(TAG, "parameters.getPreviewFormat():" + parameters.getPreviewFormat());
        if (this.getResources().getConfiguration().orientation != Configuration.ORIENTATION_LANDSCAPE) {mCamera.setDisplayOrientation(90);
        } else {mCamera.setDisplayOrientation(0);
        }
        try {mCamera.setPreviewDisplay(mHolder);
            mCamera.setPreviewCallback(mCameraPreviewCallback); // 回调要放在 startPreview() 之前
            mCamera.startPreview();} catch (Exception e) {Log.d(TAG, "Error starting camera preview:" + e.getMessage());
        }
    }

    private Camera.PreviewCallback mCameraPreviewCallback = new Camera.PreviewCallback() {
        @Override
        public void onPreviewFrame(byte[] data, Camera camera) {
            mFrameCount++;
            Log.d(TAG, "onPreviewFrame: data.length=" + data.length + ", frameCount=" + mFrameCount);
        }
    };
}

为了避免阻塞 UI 线程，在子线程中关上 camera。camera 常放在 try catch 中应用。

public class MainActivity extends AppCompatActivity {

    private static final String TAG = "rustApp";

    private Camera mCamera;
    private CameraPreview mPreview;

    @Override
    protected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        new InitCameraThread().start();
    }

    @Override
    protected void onResume() {if (null == mCamera) {if (safeCameraOpen()) {mPreview.setCamera(mCamera); // 从新获取 camera 操作权
            } else {Log.e(TAG, "无奈操作 camera");
            }
        }
        super.onResume();}

    @Override
    protected void onPause() {super.onPause();
        releaseCamera();}

    private boolean safeCameraOpen() {
        boolean qOpened = false;
        try {releaseCamera();
            mCamera = Camera.open();
            qOpened = (mCamera != null);
        } catch (Exception e) {Log.e(TAG, "failed to open Camera");
            e.printStackTrace();}
        return qOpened;
    }

    private void releaseCamera() {if (mCamera != null) {mCamera.setPreviewCallback(null);
            mCamera.release();        // release the camera for other applications
            mCamera = null;
        }
    }

    private class InitCameraThread extends Thread {
        @Override
        public void run() {super.run();
            if (safeCameraOpen()) {Log.d(TAG, "开启摄像头");
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {mPreview = new CameraPreview(MainActivity.this, mCamera);
                        FrameLayout preview = findViewById(R.id.camera_preview);
                        preview.addView(mPreview);
                    }
                });
            }
        }
    }
}

应用 TextureView 预览 Camera，取到 NV21 数据

TextureView 可用于显示内容流。内容流能够是视频或者 OpenGL 的场景。内容流可来自利用过程或是近程其它过程。

Textureview 必须在硬件加速开启的窗口中应用。若是软解，TextureView 不会显示货色。

不同于 SurfaceView，TextureView 不会建设一个独自的窗口，而是像一个惯例的 View 一样（集体认为这是个长处）。这使得 TextureView 能够被挪动，转换或是增加动画。比方，能够调用 myView.setAlpha(0.5f) 将其设置成半透明。

应用 TextureView 很简略：获取到它的 SurfaceTexture，应用 SurfaceTexture 出现内容。

CameraPreview 继承了 TextureView，内部须要传入 camera 实例。在 onSurfaceTextureAvailable 中，配置 camera，比方设置图像方向。通过设置 Camera.PreviewCallback 来获得预览数据。

import java.io.IOException;
import android.content.Context;
import android.content.res.Configuration;
import android.graphics.SurfaceTexture;
import android.hardware.Camera;
import android.util.Log;
import android.view.TextureView;

public class CameraPreview extends TextureView implements TextureView.SurfaceTextureListener {
    private static final String TAG = "rustApp";
    private Camera mCamera;

    public CameraPreview(Context context) {super(context);
    }

    public CameraPreview(Context context, Camera camera) {super(context);
        mCamera = camera;
    }

    public void setCamera(Camera camera) {this.mCamera = camera;}

    @Override
    public void onSurfaceTextureAvailable(SurfaceTexture surface, int width, int height) {Log.d(TAG, "TextureView onSurfaceTextureAvailable");
        if (this.getResources().getConfiguration().orientation != Configuration.ORIENTATION_LANDSCAPE) {mCamera.setDisplayOrientation(90);
        } else {mCamera.setDisplayOrientation(0);
        }
        try {mCamera.setPreviewCallback(mCameraPreviewCallback);
            mCamera.setPreviewTexture(surface); // 应用 SurfaceTexture
            mCamera.startPreview();} catch (IOException ioe) {// Something bad happened}
    }

    @Override
    public void onSurfaceTextureSizeChanged(SurfaceTexture surface, int width, int height) {Log.d(TAG, "TextureView onSurfaceTextureSizeChanged"); // Ignored, Camera does all the work for us
    }

    @Override
    public boolean onSurfaceTextureDestroyed(SurfaceTexture surface) {Log.d(TAG, "TextureView onSurfaceTextureDestroyed");
        mCamera.stopPreview();
        mCamera.release();
        return true;
    }

    @Override
    public void onSurfaceTextureUpdated(SurfaceTexture surface) {// Invoked every time there's a new Camera preview frame}

    private Camera.PreviewCallback mCameraPreviewCallback = new Camera.PreviewCallback() {
        @Override
        public void onPreviewFrame(byte[] data, Camera camera) {Log.d(TAG, "onPreviewFrame: data.length=" + data.length);
        }
    };
}

操作界面 TextureAct。获取 camera 操作权，初始化 CameraPreview 并增加到布局中。第一次获取 camera 时在子线程中操作。

在 onPause 中开释 camera，onResume 中尝试取回 camera 控制权。这样利用临时退回后盾时，其余利用能够操作摄像头。

public class TextureAct extends AppCompatActivity {
    private static final String TAG = "rustApp";
    private Camera mCamera;
    private CameraPreview mPreview;

    @Override
    protected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_texture);
        new InitCameraThread().start();
    }

    @Override
    protected void onResume() {if (null == mCamera) {if (safeCameraOpen()) {mPreview.setCamera(mCamera); // 从新获取 camera 操作权
            } else {Log.e(TAG, "无奈操作 camera");
            }
        }
        super.onResume();}

    @Override
    protected void onPause() {super.onPause();
        releaseCamera();}

    @Override
    protected void onDestroy() {super.onDestroy();
        releaseCamera();}

    private boolean safeCameraOpen() {
        boolean qOpened = false;
        try {releaseCamera();
            mCamera = Camera.open();
            qOpened = (mCamera != null);
        } catch (Exception e) {Log.e(TAG, "failed to open Camera");
            e.printStackTrace();}
        return qOpened;
    }

    private void releaseCamera() {if (mCamera != null) {mCamera.setPreviewCallback(null);
            mCamera.release();        // release the camera for other applications
            mCamera = null;
        }
    }

    private class InitCameraThread extends Thread {
        @Override
        public void run() {super.run();
            if (safeCameraOpen()) {Log.d(TAG, "TextureAct 开启摄像头");
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {mPreview = new CameraPreview(TextureAct.this, mCamera);
                        mPreview.setSurfaceTextureListener(mPreview);
                        FrameLayout preview = findViewById(R.id.camera_preview);
                        preview.addView(mPreview);
                    }
                });
            }
        }
    }
}

Textureview 必须在硬件加速开启的窗口中应用。android:hardwareAccelerated="true" 默认的这个属性就是 true，无需再设置。

每接到一帧数据，就会调用一次 onSurfaceTextureUpdated()。通过这个接口。可能将上来的 SurfaceTexture 送给 OpenGL 再去解决。

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