Recording Live OpenCV Processing on Android

Question

My goal is to do a couple things:

1. Use OpenCV and the JavaCameraView to process frames from the phone's camera feed
2. Enable recording of that processed video as it happens

I have both of them working, but the way I had to implement number 2 is ridiculous:

1. For each frame, write the processed Mat as an image file.
2. When the recording stops, use JCodec's Android library to stitch them together into a video file.

That works, but it comes with a ton of drawbacks: the framerate drops unbearably low during a recording, and the stitching step takes about half a second per frame, and runs out of memory for videos more than a couple seconds long- and that's after I lower my camera's resolution to make sure the images are as small as possible. Even then, the video framerate is way out of whack with reality, and the video looks insanely sped up.

This seems ridiculous for a lot of reasons, so my question is: is there a better way to do this?

Here's a little example if anybody wants to run it. This requires the OpenCV Android project available here, and the JCodec Android project available here.

Manifest.xml:

<uses-sdk
    android:minSdkVersion="8"
    android:targetSdkVersion="22"
/>

<application
    android:allowBackup="true"
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name"
    android:theme="@android:style/Theme.NoTitleBar.Fullscreen" >

    <activity
        android:name=".MainActivity"
        android:screenOrientation="landscape"
        android:configChanges="orientation|keyboardHidden|screenSize"
        android:label="@string/app_name" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>

</application>

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

MainActivity:

package com.example.videotest;

import java.io.File;
import java.util.List;

import org.opencv.android.BaseLoaderCallback;
import org.opencv.android.LoaderCallbackInterface;
import org.opencv.android.OpenCVLoader;
import org.opencv.android.CameraBridgeViewBase.CvCameraViewFrame;
import org.opencv.android.CameraBridgeViewBase.CvCameraViewListener2;
import org.opencv.core.Mat;
import org.opencv.core.Scalar;
import org.opencv.imgproc.Imgproc;

import android.app.Activity;
import android.media.MediaScannerConnection;
import android.os.Bundle;
import android.os.Environment;
import android.util.Log;
import android.view.SurfaceView;
import android.view.View;
import android.view.WindowManager;
import android.widget.Toast;

public class MainActivity extends Activity implements CvCameraViewListener2{

    private CameraView cameraView;
    private Mat edgesMat;
    private final Scalar greenScalar = new Scalar(0,255,0);
    private int resolutionIndex = 0;
    private MatVideoWriter matVideoWriter = new MatVideoWriter();


    private BaseLoaderCallback mLoaderCallback = new BaseLoaderCallback(this) {
        @Override
        public void onManagerConnected(int status) {
            switch (status) {
            case LoaderCallbackInterface.SUCCESS:
            {
                Log.i("VideoTest", "OpenCV loaded successfully");

                cameraView.enableView();

            } break;
            default:
            {
                super.onManagerConnected(status);
            } break;
            }
        }
    };


    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);

        setContentView(R.layout.activity_main);

        cameraView = (CameraView) findViewById(R.id.cameraView);
        cameraView.setVisibility(SurfaceView.VISIBLE);
        cameraView.setCvCameraViewListener(this);
    }

    @Override
    public void onPause()
    {
        super.onPause();
        if (cameraView != null){
            cameraView.disableView();
        }
    }

    @Override
    public void onResume()
    {
        super.onResume();
        OpenCVLoader.initAsync(OpenCVLoader.OPENCV_VERSION_2_4_3, this, mLoaderCallback);
    }

    public void onDestroy() {
        super.onDestroy();
        if (cameraView != null)
            cameraView.disableView();
    }

    public void onCameraViewStarted(int width, int height) {
        edgesMat = new Mat();
    }

    public void onCameraViewStopped() {
        if (edgesMat != null)
            edgesMat.release();

        edgesMat = null;
    }

    public Mat onCameraFrame(CvCameraViewFrame inputFrame) {

        Mat rgba = inputFrame.rgba();
        org.opencv.core.Size sizeRgba = rgba.size();

        int rows = (int) sizeRgba.height;
        int cols = (int) sizeRgba.width;

        int left = cols / 8;
        int top = rows / 8;
        int width = cols * 3 / 4;
        int height = rows * 3 / 4;

        //get sub-image
        Mat rgbaInnerWindow = rgba.submat(top, top + height, left, left + width);

        //create edgesMat from sub-image
        Imgproc.Canny(rgbaInnerWindow, edgesMat, 100, 100);

        Mat colorEdges = new Mat();
        Mat killMe = colorEdges;
        edgesMat.copyTo(colorEdges);
        Imgproc.cvtColor(colorEdges, colorEdges, Imgproc.COLOR_GRAY2BGRA);


        colorEdges = colorEdges.setTo(greenScalar, edgesMat);
        colorEdges.copyTo(rgbaInnerWindow, edgesMat);

        killMe.release();
        colorEdges.release();

        rgbaInnerWindow.release();

        if(matVideoWriter.isRecording()){
            matVideoWriter.write(rgba);
        }

        return rgba;
    }


    public void changeResolution(View v){
        List<android.hardware.Camera.Size> cameraResolutionList = cameraView.getResolutionList();
        resolutionIndex++;
        if(resolutionIndex >= cameraResolutionList.size()){
            resolutionIndex = 0;
        }

        android.hardware.Camera.Size resolution = cameraResolutionList.get(resolutionIndex);
        cameraView.setResolution(resolution.width, resolution.height);
        resolution = cameraView.getResolution();
        String caption = Integer.valueOf(resolution.width).toString() + "x" + Integer.valueOf(resolution.height).toString();
        Toast.makeText(this, caption, Toast.LENGTH_SHORT).show();
    }

    public void startVideo(View v){

        if(matVideoWriter.isRecording()){
            matVideoWriter.stop();
            File file = new File(getExternalFilesDir(null), "VideoTest/images/");
            for(String img : file.list()){
                String scanMe = new File(file, img).getAbsolutePath();
                MediaScannerConnection.scanFile(this, new String[]{scanMe}, null, null);
                Log.i("VideoTest", "Scanning: " +scanMe);
            }

            file = new File(file, "video.mp4");
            MediaScannerConnection.scanFile(this, new String[]{file.getAbsolutePath()}, null, null);

        }
        else{ 

            String state = Environment.getExternalStorageState();
            Log.i("VideoTest", "state: " + state);

            File ext = getExternalFilesDir(null);
            Log.i("VideoTest", "ext: " + ext.getAbsolutePath());


            File file = new File(getExternalFilesDir(null), "VideoTest/images/");
            if(!file.exists()){
                boolean success = file.mkdirs();

                Log.i("VideoTest", "mkdirs: " + success);
            }
            else{
                Log.i("VideoTest", "file exists.");
            }

            Log.i("VideoTest", "starting recording: " + file.getAbsolutePath());

            matVideoWriter.start(file);
        }

    }

}

CameraView:

package com.example.videotest;

import java.io.FileOutputStream;
import java.util.List;

import org.opencv.android.JavaCameraView;

import android.content.Context;
import android.hardware.Camera;
import android.hardware.Camera.PictureCallback;
import android.util.AttributeSet;
import android.util.Log;

public class CameraView extends JavaCameraView{

    private String mPictureFileName;

    public CameraView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public List<String> getEffectList() {
        return mCamera.getParameters().getSupportedColorEffects();
    }

    public boolean isEffectSupported() {
        return (mCamera.getParameters().getColorEffect() != null);
    }

    public String getEffect() {
        return mCamera.getParameters().getColorEffect();
    }

    public void setEffect(String effect) {
        Camera.Parameters params = mCamera.getParameters();
        params.setColorEffect(effect);
        mCamera.setParameters(params);
    }

    public List<android.hardware.Camera.Size> getResolutionList() {
        return mCamera.getParameters().getSupportedPreviewSizes();
    }

    public void setResolution(int width, int height) {
        disconnectCamera();
        mMaxHeight = height;
        mMaxWidth = width;
        connectCamera(getWidth(), getHeight());
    }

    public android.hardware.Camera.Size getResolution() {
        return mCamera.getParameters().getPreviewSize();
    }

}

MatVideoWriter:

package com.example.videotest;

import java.io.File;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

import org.jcodec.api.android.SequenceEncoder;
import org.opencv.core.Mat;
import org.opencv.highgui.Highgui;
import org.opencv.imgproc.Imgproc;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.util.Log;

public class MatVideoWriter {

    boolean recording;
    File dir;
    int imageIndex = 0;

    public void start(File dir){
        this.dir = dir;
        recording = true;
    }

    public void stop(){
        recording = false;

        try{
            File file = new File(dir, "video.mp4");
            SequenceEncoder encoder = new SequenceEncoder(file);

            List<File> files = Arrays.asList(dir.listFiles());
            Collections.sort(files, new Comparator<File>(){
                @Override
                public int compare(File lhs, File rhs) {
                    return lhs.getName().compareTo(rhs.getName());
                }
            });

            for(File f : files){
                Log.i("VideoTest", "Encoding image: " + f.getAbsolutePath());
                try{
                    Bitmap frame = BitmapFactory.decodeFile(f.getAbsolutePath());
                    encoder.encodeImage(frame);
                }
                catch(Exception e){
                    e.printStackTrace();
                }

            }
            encoder.finish();
        }
        catch(Exception e){
            e.printStackTrace();
        }
    }

    public void write(Mat mat){

        //convert from BGR to RGB
        Mat rgbMat = new Mat();
        Imgproc.cvtColor(mat, rgbMat, Imgproc.COLOR_BGR2RGB);

        File file = new File(dir, "img" + imageIndex + ".png");

        String filename = file.toString();
        boolean success = Highgui.imwrite(filename, rgbMat);

        Log.i("VideoTest", "Success writing img" + imageIndex +".png: " + success);

        imageIndex++;
    }

    public boolean isRecording() {
        return recording;
    }
}

Edit: I haven't received any comments or answers, so I've crossposted to the OpenCV forum here.

Traipse

Why don't you use the default recording activity built-in from android itself? After that you can retrieve the video file and to whatever you want with it. – Audreaaudres

@HaDang Because I need to do the processing live, not after the recording. The default recording activity does not give you access to the individual frames. – Traipse

How about pushing incoming images into a queue after processing, and periodically pass the queue to another thread to do the saving? – Audreaaudres

@HaDang I suppose I could do that, but that still seems like a crazy solution. I've been pretty shocked to find that there isn't a standard way to export video as it's being processed like this. Seems like a pretty major feature for OpenCV developers. – Traipse

@Kenvin Workman: Did you try VideoWriter? It seems that someone succeeded in generating its java binding. – Audreaaudres

@HaDang Unfortunately, VideoWriter does not work on Android, which is why I went with jcodec: answers.opencv.org/question/29068/… (I will also note that exporting the images on another thread would not fix the problems with JCodec running out of memory) – Traipse

Let us continue this discussion in chat. – Audreaaudres

Is it a requeriment?, the utilization of the JavaCameraView class and the Android sdk for OpenCV? It will be better to implement the processing part of the code in C++ with OpenCV and send it an array of bytes – Shannon

Answer 1

@HaDang pointed me to these links:

http://www.walking-productions.com/notslop/2013/01/16/android-live-streaming-courtesy-of-javacv-and-ffmpeg/

https://code.google.com/p/javacv/source/browse/samples/RecordActivity.java

That example uses a Java wrapper of FFMPEG to do the video recording. This project is a pretty useful starting point for anybody wanting to do the same: https://github.com/vanevery/JavaCV_0.3_stream_test

I took that above project and hammered it into my example. It's very messy, but it works:

package com.example.videotest;


import java.io.File;
import java.io.IOException;
import java.nio.ShortBuffer;
import java.util.List;

import org.opencv.android.BaseLoaderCallback;
import org.opencv.android.LoaderCallbackInterface;
import org.opencv.android.OpenCVLoader;
import org.opencv.android.CameraBridgeViewBase.CvCameraViewFrame;
import org.opencv.android.CameraBridgeViewBase.CvCameraViewListener2;
import org.opencv.core.Mat;
import org.opencv.core.Scalar;
import org.opencv.imgproc.Imgproc;

import com.googlecode.javacv.FFmpegFrameRecorder;
import com.googlecode.javacv.FrameRecorder.Exception;
import com.googlecode.javacv.cpp.opencv_core.IplImage;

import android.app.Activity;
import android.media.AudioFormat;
import android.media.AudioRecord;
import android.media.MediaRecorder;
import android.media.MediaScannerConnection;
import android.os.Bundle;
import android.os.Environment;
import android.util.Log;
import android.view.SurfaceView;
import android.view.View;
import android.view.WindowManager;
import android.widget.Toast;

public class MainActivity extends Activity implements CvCameraViewListener2{

    private CameraView cameraView;
    private Mat edgesMat;
    private final Scalar greenScalar = new Scalar(0,255,0);
    private int resolutionIndex = 0;

    private IplImage videoImage = null;

    boolean recording = false;
    private volatile FFmpegFrameRecorder recorder;

    private int sampleAudioRateInHz = 44100;
    private int imageWidth = 320;
    private int imageHeight = 240;
    private int frameRate = 30;

    private Thread audioThread;
    volatile boolean runAudioThread = true;
    private AudioRecord audioRecord;
    private AudioRecordRunnable audioRecordRunnable;

    private String ffmpeg_link;

    long startTime = 0;

    private String LOG_TAG = "VideoTest";

    private BaseLoaderCallback mLoaderCallback = new BaseLoaderCallback(this) {
        @Override
        public void onManagerConnected(int status) {
            switch (status) {
            case LoaderCallbackInterface.SUCCESS:
                Log.i("VideoTest", "OpenCV loaded successfully");
                cameraView.enableView();
                break;
            default:
                super.onManagerConnected(status);
                break;
            }
        }
    };


    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);

        setContentView(R.layout.activity_main);

        cameraView = (CameraView) findViewById(R.id.cameraView);
        cameraView.setVisibility(SurfaceView.VISIBLE);
        cameraView.setCvCameraViewListener(this);
    }

    private void initRecorder() {
        Log.w(LOG_TAG,"initRecorder");

        int depth = com.googlecode.javacv.cpp.opencv_core.IPL_DEPTH_8U;
        int channels = 4;

        // if (yuvIplimage == null) {
        // Recreated after frame size is set in surface change method
        videoImage = IplImage.create(imageWidth, imageHeight, depth, channels);
        //yuvIplimage = IplImage.create(imageWidth, imageHeight, IPL_DEPTH_32S, 2);

        Log.v(LOG_TAG, "IplImage.create");
        // }

        File videoFile = new File(getExternalFilesDir(null), "VideoTest/images/video.mp4");
        boolean mk = videoFile.getParentFile().mkdirs();
        Log.v(LOG_TAG, "Mkdir: " + mk);

        boolean del = videoFile.delete();
        Log.v(LOG_TAG, "del: " + del);

        try {
            boolean created = videoFile.createNewFile();
            Log.v(LOG_TAG, "Created: " + created);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        ffmpeg_link = videoFile.getAbsolutePath();
        recorder = new FFmpegFrameRecorder(ffmpeg_link, imageWidth, imageHeight, 1);
        Log.v(LOG_TAG, "FFmpegFrameRecorder: " + ffmpeg_link + " imageWidth: " + imageWidth + " imageHeight " + imageHeight);

        recorder.setFormat("mp4");
        Log.v(LOG_TAG, "recorder.setFormat(\"mp4\")");

        recorder.setSampleRate(sampleAudioRateInHz);
        Log.v(LOG_TAG, "recorder.setSampleRate(sampleAudioRateInHz)");

        // re-set in the surface changed method as well
        recorder.setFrameRate(frameRate);
        Log.v(LOG_TAG, "recorder.setFrameRate(frameRate)");

        // Create audio recording thread
        audioRecordRunnable = new AudioRecordRunnable();
        audioThread = new Thread(audioRecordRunnable);
    }

    @Override
    public void onPause()
    {
        super.onPause();
        if (cameraView != null){
            cameraView.disableView();
        }
    }

    @Override
    public void onResume()
    {
        super.onResume();
        OpenCVLoader.initAsync(OpenCVLoader.OPENCV_VERSION_2_4_3, this, mLoaderCallback);
    }

    public void onDestroy() {
        super.onDestroy();
        if (cameraView != null)
            cameraView.disableView();
    }

    public void onCameraViewStarted(int width, int height) {
        edgesMat = new Mat();
    }

    public void onCameraViewStopped() {
        if (edgesMat != null)
            edgesMat.release();

        edgesMat = null;
    }

    public Mat onCameraFrame(CvCameraViewFrame inputFrame) {

        Mat rgba = inputFrame.rgba();
        org.opencv.core.Size sizeRgba = rgba.size();

        int rows = (int) sizeRgba.height;
        int cols = (int) sizeRgba.width;

        int left = cols / 8;
        int top = rows / 8;
        int width = cols * 3 / 4;
        int height = rows * 3 / 4;

        //get sub-image
        Mat rgbaInnerWindow = rgba.submat(top, top + height, left, left + width);

        //create edgesMat from sub-image
        Imgproc.Canny(rgbaInnerWindow, edgesMat, 100, 100);

        Mat colorEdges = new Mat();
        Mat killMe = colorEdges;
        edgesMat.copyTo(colorEdges);
        Imgproc.cvtColor(colorEdges, colorEdges, Imgproc.COLOR_GRAY2BGRA);


        colorEdges = colorEdges.setTo(greenScalar, edgesMat);
        colorEdges.copyTo(rgbaInnerWindow, edgesMat);

        killMe.release();
        colorEdges.release();

        rgbaInnerWindow.release();

        if(recording){
            byte[] byteFrame = new byte[(int) (rgba.total() * rgba.channels())];
            rgba.get(0, 0, byteFrame);
            onFrame(byteFrame);
        }

        return rgba;
    }

    public void stopRecording() {
        // This should stop the audio thread from running
        runAudioThread = false;

        if (recorder != null) {
            Log.v(LOG_TAG,"Finishing recording, calling stop and release on recorder");
            try {
                recorder.stop();
                recorder.release();
            } catch (FFmpegFrameRecorder.Exception e) {
                e.printStackTrace();
            }
            recorder = null;
        }

        MediaScannerConnection.scanFile(MainActivity.this, new String[]{ffmpeg_link}, null, null);
    }


    public void changeResolution(View v){
        List<android.hardware.Camera.Size> cameraResolutionList = cameraView.getResolutionList();
        resolutionIndex++;
        if(resolutionIndex >= cameraResolutionList.size()){
            resolutionIndex = 0;
        }

        android.hardware.Camera.Size resolution = cameraResolutionList.get(resolutionIndex);
        cameraView.setResolution(resolution.width, resolution.height);
        resolution = cameraView.getResolution();
        String caption = Integer.valueOf(resolution.width).toString() + "x" + Integer.valueOf(resolution.height).toString();
        Toast.makeText(this, caption, Toast.LENGTH_SHORT).show();

        imageWidth = resolution.width;
        imageHeight = resolution.height;

        frameRate = cameraView.getFrameRate();

        initRecorder();
    }

    int frames = 0;

    private void onFrame(byte[] data){

        if (videoImage != null && recording) {
            long videoTimestamp = 1000 * (System.currentTimeMillis() - startTime);

            // Put the camera preview frame right into the yuvIplimage object
            videoImage.getByteBuffer().put(data);

            try {

                // Get the correct time
                recorder.setTimestamp(videoTimestamp);

                // Record the image into FFmpegFrameRecorder
                recorder.record(videoImage);

                frames++;

                Log.i(LOG_TAG, "Wrote Frame: " + frames);

            } 
            catch (FFmpegFrameRecorder.Exception e) {
                Log.v(LOG_TAG,e.getMessage());
                e.printStackTrace();
            }
        }

    }

    public void startVideo(View v){

        recording = !recording;

        Log.i(LOG_TAG, "Recording: " + recording);

        if(recording){
            startTime = System.currentTimeMillis();
            try {
                recorder.start();

                Log.i(LOG_TAG, "STARTED RECORDING.");

            } catch (Exception e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        else{
            stopRecording();
        }
    }



    class AudioRecordRunnable implements Runnable {

        @Override
        public void run() {
            // Set the thread priority
            android.os.Process.setThreadPriority(android.os.Process.THREAD_PRIORITY_URGENT_AUDIO);

            // Audio
            int bufferSize;
            short[] audioData;
            int bufferReadResult;

            bufferSize = AudioRecord.getMinBufferSize(sampleAudioRateInHz, 
                    AudioFormat.CHANNEL_CONFIGURATION_MONO, AudioFormat.ENCODING_PCM_16BIT);
            audioRecord = new AudioRecord(MediaRecorder.AudioSource.MIC, sampleAudioRateInHz, 
                    AudioFormat.CHANNEL_CONFIGURATION_MONO, AudioFormat.ENCODING_PCM_16BIT, bufferSize);

            audioData = new short[bufferSize];

            Log.d(LOG_TAG, "audioRecord.startRecording()");
            audioRecord.startRecording();

            // Audio Capture/Encoding Loop
            while (runAudioThread) {
                // Read from audioRecord
                bufferReadResult = audioRecord.read(audioData, 0, audioData.length);
                if (bufferReadResult > 0) {
                    //Log.v(LOG_TAG,"audioRecord bufferReadResult: " + bufferReadResult);

                    // Changes in this variable may not be picked up despite it being "volatile"
                    if (recording) {
                        try {
                            // Write to FFmpegFrameRecorder
                            recorder.record(ShortBuffer.wrap(audioData, 0, bufferReadResult));
                        } catch (FFmpegFrameRecorder.Exception e) {
                            Log.v(LOG_TAG,e.getMessage());
                            e.printStackTrace();
                        }
                    }
                }
            }
            Log.v(LOG_TAG,"AudioThread Finished");

            /* Capture/Encoding finished, release recorder */
            if (audioRecord != null) {
                audioRecord.stop();
                audioRecord.release();
                audioRecord = null;

                MediaScannerConnection.scanFile(MainActivity.this, new String[]{ffmpeg_link}, null, null);

                Log.v(LOG_TAG,"audioRecord released");
            }
        }
    }

}

Traipse

Answer 2

I've solved a similar problem by creating a MediaRecorder and passing it to a OpenCV CameraBridgeViewBase, which I've modified as follows.

protected MediaRecorder mRecorder;
protected Surface mSurface = null;

public void setRecorder(MediaRecorder rec) {
    mRecorder = rec;
    if (mRecorder != null) {
        mSurface = mRecorder.getSurface();
    }

and

protected void deliverAndDrawFrame(CvCameraViewFrame frame) {
    Mat modified;

    if (mListener != null) {
        modified = mListener.onCameraFrame(frame);
    } else {
        modified = frame.rgba();
    }

    boolean bmpValid = true;
    if (modified != null) {
        try {
            Utils.matToBitmap(modified, mCacheBitmap);
        } catch(Exception e) {
            Log.e(TAG, "Mat type: " + modified);
            Log.e(TAG, "Bitmap type: " + mCacheBitmap.getWidth() + "*" + mCacheBitmap.getHeight());
            Log.e(TAG, "Utils.matToBitmap() throws an exception: " + e.getMessage());
            bmpValid = false;
        }
    }

    if (bmpValid && mCacheBitmap != null) {
        Canvas canvas;

        if (mRecorder != null) {
            canvas = mSurface.lockCanvas(null);

            canvas.drawColor(0, android.graphics.PorterDuff.Mode.CLEAR);
            Log.d(TAG, "mStretch value: " + mScale);

            if (mScale != 0) {
                canvas.drawBitmap(mCacheBitmap, new Rect(0,0,mCacheBitmap.getWidth(), mCacheBitmap.getHeight()),
                     new Rect((int)((canvas.getWidth() - mScale*mCacheBitmap.getWidth()) / 2),
                     (int)((canvas.getHeight() - mScale*mCacheBitmap.getHeight()) / 2),
                     (int)((canvas.getWidth() - mScale*mCacheBitmap.getWidth()) / 2 + mScale*mCacheBitmap.getWidth()),
                     (int)((canvas.getHeight() - mScale*mCacheBitmap.getHeight()) / 2 + mScale*mCacheBitmap.getHeight())), null);
            } else {
                 canvas.drawBitmap(mCacheBitmap, new Rect(0,0,mCacheBitmap.getWidth(), mCacheBitmap.getHeight()),
                     new Rect((canvas.getWidth() - mCacheBitmap.getWidth()) / 2,
                     (canvas.getHeight() - mCacheBitmap.getHeight()) / 2,
                     (canvas.getWidth() - mCacheBitmap.getWidth()) / 2 + mCacheBitmap.getWidth(),
                     (canvas.getHeight() - mCacheBitmap.getHeight()) / 2 + mCacheBitmap.getHeight()), null);
            }

            if (mFpsMeter != null) {
                mFpsMeter.measure();
                mFpsMeter.draw(canvas, 20, 30);
            }
            mSurface.unlockCanvasAndPost(canvas);
        } 

    }

    ...

}

I've left the original part of deliverAndDrawFrame as is, so that it keeps displaying the output to the original surface. This way I can process images from a camera by implementing onCameraFrame in MainActivity and save the resulting images to a video, without the need for ffmpeg.

EDIT I've set up the MediaRecorder as follows

recorder.setAudioSource(MediaRecorder.AudioSource.MIC);
recorder.setVideoSource(MediaRecorder.VideoSource.SURFACE);

CamcorderProfile cpHigh = CamcorderProfile.get(CamcorderProfile.QUALITY_HIGH);
recorder.setProfile(cpHigh);
recorder.setOutputFile("out.mp4");
recorder.setVideoSize(mOpenCvCameraView.mFrameWidth, mOpenCvCameraView.mFrameHeight);

recorder.setOnInfoListener(this);
recorder.setOnErrorListener(this);
recorder.prepare();

register it with the OpenCvCameraView

mOpenCvCameraView.setRecorder(recorder);

and start recording

recorder.start();

Politi

Does the modified canvas get recorded as well? I tried your solution but had no joy – Omit

Yes, that is the whole point of it. When the mRecorder in CameraBridgeViewBase is set, then the canvas is passed to the mRecorder to be recorded. – Politi

That's amazing. I spent around 5 hours trying to implement this yesterday but to no avail. I'm quite confused about the MediaRecorder class as I can't find many examples - when I set the MediaRecorder object to use a surface, do I set the preview display to my altered CameraBridgeViewBase? I do get the basic outline of your method but I'm just stuck understanding the over all flow! – Omit

I've updated the answer with the initialization of MediaRecorder. It took me some time as well, to get it right. – Politi

Awesome! Can't wait to give this a go tonight! Thanks! – Omit

Got this working perfectly! This is honestly the best solution and far easier to implement compared to FFmpeg. Thanks again. Just a note to anyone else trying this as it wasn't obvious to me at the start, but you have to draw onto both canvases in the deliverAndDraw method. – Omit

Hi. Do you have the full code available anywhere? I'm having trouble with MediaRecorder and JavaCameraView working together as JavaCameraView's mCamera method is protected, and I need to pass it in to MediaRecorder. – Barna

Sorry, I don't have access to the source codes anymore. – Politi

No worries. To add on to this, did you not experience low fps due to 2 bitmaps being drawn simultaneously? – Barna

It was slightly slower, but used only when we wanted to record video of the screen, which was not the main goal of the application, so we did not mind. – Politi

Camera preview not available, only black screen has been appearing. This is the same approach and same problem... #38494660 – Ryley

this one doesn't work on all devices.. mediarecorder.stop method fails. did you meet such issue? – Niigata

@JohnM what do you mean both canvases? – Niigata

Answer 3

Try to compile FFMPEG for Android for live video processing. Integration with android and openCV,this link will help:

http://www.jayrambhia.com/blog/ffmpeg-opencv-android

Precept

Update your link, last forward slash must be removed. ;) – Ryley

Answer 4

Another option that works only on Lollipop and Marshmallow is to use the new MediaProjectionManager to capture and record what's happening on your device's screen. A great example is here:

http://www.mattsnider.com/video-recording-with-mediaprojectionmanager/

It's totally independent of your device's camera and doesn't need any access to it or whatever you're doing with OpenCV. It's just recording whatever you have displayed on your screen.

Prolongation