Added preview callback

library/src/main/api14/com/google/android/cameraview/Camera1.java

@@ -121,6 +121,17 @@ void setUpPreview() {
             } else {
                 mCamera.setPreviewTexture((SurfaceTexture) mPreview.getSurfaceTexture());
             }
+
+            mCamera.setPreviewCallback(new Camera.PreviewCallback() {
+                @Override
+                public void onPreviewFrame(byte[] data, Camera camera) {
+                    final Camera.Parameters parameters = camera.getParameters();
+                    final int width = parameters.getPreviewSize().width;
+                    final int height = parameters.getPreviewSize().height;
+                    mCallback.onPreviewFrame(data, parameters.getPreviewFormat(), width, height);
+                }
+            });
+
         } catch (IOException e) {
             throw new RuntimeException(e);
         }

library/src/main/api21/com/google/android/cameraview/Camera2.java

@@ -31,6 +31,7 @@
 import android.media.Image;
 import android.media.ImageReader;
 import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.util.Log;
 import android.util.SparseIntArray;
 import android.view.Surface;
@@ -156,19 +157,26 @@ public void onReady() {
 
         @Override
         public void onImageAvailable(ImageReader reader) {
-            try (Image image = reader.acquireNextImage()) {
-                Image.Plane[] planes = image.getPlanes();
-                if (planes.length > 0) {
-                    ByteBuffer buffer = planes[0].getBuffer();
-                    byte[] data = new byte[buffer.remaining()];
-                    buffer.get(data);
-                    mCallback.onPictureTaken(data);
-                }
+            byte[] data = getByteDataFromImageReader(reader);
+            if (data != null) {
+                mCallback.onPictureTaken(data);
             }
         }
-
     };
 
+    private final ImageReader.OnImageAvailableListener mOnPreviewImageAvailableListener
+            = new ImageReader.OnImageAvailableListener() {
+
+        @Override
+        public void onImageAvailable(ImageReader reader) {
+            byte[] data = getByteDataFromImageReader(reader);
+            if (data != null) {
+                mCallback.onPreviewFrame(data, reader.getImageFormat(),
+                        reader.getWidth(),
+                        reader.getHeight());
+            }
+        }
+    };
 
     private String mCameraId;
 
@@ -182,6 +190,8 @@ public void onImageAvailable(ImageReader reader) {
 
     private ImageReader mImageReader;
 
+    private ImageReader mCallbackImageDataReader;
+
     private final SizeMap mPreviewSizes = new SizeMap();
 
     private final SizeMap mPictureSizes = new SizeMap();
@@ -232,6 +242,11 @@ void stop() {
             mImageReader.close();
             mImageReader = null;
         }
+
+        if (mCallbackImageDataReader != null) {
+            mCallbackImageDataReader.close();
+            mCallbackImageDataReader = null;
+        }
     }
 
     @Override
@@ -435,11 +450,49 @@ protected void collectPictureSizes(SizeMap sizes, StreamConfigurationMap map) {
 
     private void prepareImageReader() {
         Size largest = mPictureSizes.sizes(mAspectRatio).last();
-        mImageReader = ImageReader.newInstance(largest.getWidth(), largest.getHeight(),
+        initImageReader(largest.getWidth(), largest.getHeight());
+
+        Size size = chooseOptimalSize();
+        initCallbackImageDataReader(size.getWidth(), size.getHeight());
+    }
+
+    private void initImageReader(int width, int height){
+        mImageReader = ImageReader.newInstance(width, height,
                 ImageFormat.JPEG, /* maxImages */ 2);
         mImageReader.setOnImageAvailableListener(mOnImageAvailableListener, null);
     }
 
+    private void initCallbackImageDataReader(int width, int height) {
+
+        if (mCallbackImageDataReader != null) {
+            mCallbackImageDataReader.close();
+        }
+
+        mCallbackImageDataReader = ImageReader.newInstance(width, height,
+                ImageFormat.NV21, /* maxImages */ 1);
+        mCallbackImageDataReader.setOnImageAvailableListener(mOnPreviewImageAvailableListener, null);
+    }
+
+    /**
+     * Extract the byte data from the ImageReader
+     * @param reader
+     * @return byte array or null if failed
+     */
+    @Nullable
+    private byte[] getByteDataFromImageReader(@NonNull ImageReader reader) {
+        byte[] data = null;
+        try (Image image = reader.acquireNextImage()) {
+            Image.Plane[] planes = image.getPlanes();
+            if (planes.length > 0) {
+                ByteBuffer buffer = planes[0].getBuffer();
+                data = new byte[buffer.remaining()];
+                buffer.get(data);
+            }
+        }
+        return data;
+    }
+
+
     /**
      * <p>Starts opening a camera device.</p>
      * <p>The result will be processed in {@link #mCameraDeviceCallback}.</p>
@@ -463,11 +516,14 @@ void startCaptureSession() {
         }
         Size previewSize = chooseOptimalSize();
         mPreview.setBufferSize(previewSize.getWidth(), previewSize.getHeight());
+
         Surface surface = mPreview.getSurface();
         try {
             mPreviewRequestBuilder = mCamera.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
             mPreviewRequestBuilder.addTarget(surface);
-            mCamera.createCaptureSession(Arrays.asList(surface, mImageReader.getSurface()),
+            mPreviewRequestBuilder.addTarget(mCallbackImageDataReader.getSurface());
+            mCamera.createCaptureSession(Arrays.asList(surface, mImageReader.getSurface(),
+                    mCallbackImageDataReader.getSurface()),
                     mSessionCallback, null);
         } catch (CameraAccessException e) {
             throw new RuntimeException("Failed to start camera session");

library/src/main/base/com/google/android/cameraview/CameraViewImpl.java

@@ -77,6 +77,7 @@ interface Callback {
 
         void onPictureTaken(byte[] data);
 
+        void onPreviewFrame(byte[] data, int format, int width, int height);
     }
 
 }

library/src/main/java/com/google/android/cameraview/CameraView.java

@@ -448,6 +448,13 @@ public void onPictureTaken(byte[] data) {
             }
         }
 
+        @Override
+        public void onPreviewFrame(byte[] data, int format, int width, int height) {
+            for (Callback callback : mCallbacks) {
+                callback.onPreviewFrame(data, format, width, height);
+            }
+        }
+
         public void reserveRequestLayoutOnOpen() {
             mRequestLayoutOnOpen = true;
         }
@@ -534,6 +541,17 @@ public void onCameraClosed(CameraView cameraView) {
          */
         public void onPictureTaken(CameraView cameraView, byte[] data) {
         }
+
+        /**
+         * Called when a preview frame is rendered
+         * @param data raw byte data
+         * @param format data format
+         * @param width image width
+         * @param height image height
+         */
+        public void onPreviewFrame(byte[] data, int format, int width, int height){
+        }
+
     }
 
 }