Develop Reference

Digital persona SDK - native problems

I am using in my app Digital Persona SDK for fingerprint identification.
When i use the identify function on less then 250 fmds it works fine.
Engine.Candidate candidates[] = m_engine.Identify(searchedFmd, 0, fmdArray, DEFAULT_THRESHOLD, 1); //fmdArray < 250
But with fmdArray > 250 it gives me a native runtime error:
A/art: art/runtime/indirect_reference_table.cc:132] JNI ERROR (app bug): local reference table overflow (max=512)
Now i runned this app on couple of android devices and came to conclusion that my app crushes with fmdArray > 250 when its running on android 7. But android 8 works fine. In 8 i can preform a check on even 4000 fmds and it works fine.
But i need to run this code in a specific device, that running android 7.
I tried to run it in couple of threads of 250 fmds only. But after single run there is another problem with the SDK. On the second run it doesnt works.
This is what i do:
First i get a fingerprint capture that i want to identify:
Reader.CaptureResult capture = m_reader.Capture(fidFormat, UrUSDK.DefaultImageProcessing, m_DPI, timeout);
// In second run, code after this line is not executed.
// My guees its not coming back from native. No exeptions. No errors.
...
Fmd scannedFmd = m_engine.CreateFmd(capture.image, fmdFormat);
...
int index = identifyFinger(fmds, scannedFmd);
...
private int identifyFinger(List<Fmd> fmdSearchArray, Fmd scannedFmd) {
List<List<Fmd>> lists = splitToChunks(fmdSearchArray);
AtomicInteger index = new AtomicInteger(-1);
List<Callable<Void>> threads = new ArrayList<>(lists.size());
AtomicInteger iteratorIndex = new AtomicInteger(0);
for (int i = 0; i < lists.size(); i++) {
int currentChunk = i;
Callable<Void> thread = () -> {
System.out.println(Thread.currentThread().getName() + " with chunk: " + iteratorIndex.getAndIncrement());
Fmd[] fmds = lists.get(currentChunk).toArray(new Fmd[IDENTIFY_BOUNDARY]);
try {
Engine.Candidate[] candidates = m_engine.Identify(scannedFmd, 0, fmds, threshold, 1);
if (candidates.length > 0) {
index.set(candidates[0].fmd_index + (currentChunk * IDENTIFY_BOUNDARY));
}
} catch (UareUException e) {
}
System.out.println(Thread.currentThread().getName() + " with chunk: " + currentChunk + " finished!");
return null;
};
threads.add(thread);
}
try {
List<Future<Void>> futures = executorService.invokeAll(threads);
System.out.println("All threads finished: " + index.get());
return index.get();
} catch (InterruptedException e) {
e.printStackTrace();
return -1;
}
}
...
private List<List<Fmd>> splitToChunks(List<Fmd> fmdSearchArray) {
int size = fmdSearchArray.size();
List<List<Fmd>> lists;
if (size > IDENTIFY_BOUNDARY) {
int chunks = size / IDENTIFY_BOUNDARY;
if (size % IDENTIFY_BOUNDARY > 0) {
chunks++;
}
lists = new ArrayList<>(chunks);
for (int i = 0; i < chunks; i++) {
if (i + 1 == chunks) {
lists.add(new ArrayList<>(fmdSearchArray.subList(i * IDENTIFY_BOUNDARY, size)));
break;
}
lists.add(new ArrayList<>(fmdSearchArray.subList(i * IDENTIFY_BOUNDARY, (i + 1) * IDENTIFY_BOUNDARY)));
}
} else {
lists = new ArrayList<>(1);
lists.add(fmdSearchArray);
}
return lists;
}
The problem with this code is that it runs once. But at another try it doesnt come back from the native code of Caprture call.
So my question is:
How i can overcome this and make it work from my java code?
Or at least what is the direction of the solution?

The root cause is that this Identify function holds on to at least two references per returned Candidate after pushing it to the result array. It should instead release the references after pushing, so its use of the (limited) local reference table remain constant. You should file a bug about that.
The simplest workaround for now is to cut your fmdArray into 250-sized chunks and call Identify for each chunk.

Xamarin multiplatform - Video from jpeg sequence

I want to know how I can display video from jpegs in Xamarin (all platforms).
My jpegs are being streamed from a http client stream sent by a popular video surveillance management software.
My jpegs are in the form of byte[] and I get about 10 jpegs/second. This format is imposed.
I tried rapidly changing the Source on a Image but it results in severe fliquering on Android. This seems to work on Windows phone but not so good performance.
How can I create a videoplayer for each one? Unless I am wrond, the existing components cannot do this.
Best,

Thank you Jason! Works great, very fluid rendering!!
Simply add the SkiaSharp.Views.Forms with NuGet to the project and voila!
Here is what that would look like in code (shared project):
// Content page initialization
private void InitUI() {
Title = "Xamavideo";
var button = new Button
{
Text = "Connect!"
};
Label label = new Label
{
Text = ""
};
var scroll = new ScrollView();
scroll.BackgroundColor = Color.Black;
Content = scroll;
var stack = new StackLayout
{
Padding = 40,
Spacing = 10
};
//Add a SKCanvasView item to the stack
var videoCanvas = new SKCanvasView
{
HeightRequest = 400,
WidthRequest = 600,
};
videoCanvas.PaintSurface += OnCanvasViewPaintSurface;
stack.Children.Add(videoCanvas);
}
//Create the event handler
void OnCanvasViewPaintSurface(object sender, SKPaintSurfaceEventArgs args)
{
SKImageInfo info = args.Info;
SKSurface surface = args.Surface;
// using (var stream = new SKManagedStream(fileStream))
if (lastFrame == null) return;
using (var canvas = surface.Canvas)
// use KBitmap.Decode to decode the byte[] in jpeg format
using (var bitmap = SKBitmap.Decode(lastFrame))
using (var paint = new SKPaint())
{
// clear the canvas / fill with black
canvas.DrawColor(SKColors.Black);
canvas.DrawBitmap(bitmap, SKRect.Create(640, 480), paint);
}
}
void UpdateFrame(VideoClient client){
//Use this to update the canvas:
byte[] lastFrame = client.imageBytes;
videoCanvas.InvalidateSurface();
}

Get personal app code and display it

I am trying to get the app code and display it, for an example if button X starts a new activity then a textView displays the whole method
I reached only how can I display code in HTML format from this question
But is there is a way to get the code of my app out, I think that there are 2 ways
An Internal one by getting it by the app itself
An External one by reading the java file then filtering it and getting the text of the method
Is there are any ideas about that?
Thanks in advance

The above is not currently possible as mentioned by others is the comments. What i can suggest is shipping your application with the source code in the assets folder and using a helper function to extract a certain methods from the source at runtime (your second proposed approach). I have written example code but it is in pure java and needs to be ported to android (a few lines).
NB: You may need to reformat the code after extraction depending on your use case.
Hope it helps :)
The code for the helper method:
static String getTheCode(String classname ,String methodSignature ) throws FileNotFoundException {
//**********************A few lines of code below need changing when porting ***********//
// open file, your will be in the assets folder not in the home dir of user, don't forget the .java extension when porting
File file = new File(System.getProperty("user.home") +"/"+ classname +".java");
// get the source, you can use FileInputReader or some reader supported by android
Scanner scanner = new Scanner(file);
String source = "";
while(scanner.hasNext()) {
source += " "+ scanner.next();
}
//**********************The above code needs changing when porting **********//
// extract code using the method signature
methodSignature = methodSignature.trim();
source = source.trim();
//appending { to differentiate from argument as it can be matched also if in the same file
methodSignature = methodSignature+"{";
//making sure we find what we are looking for
methodSignature = methodSignature.replaceAll("\\s*[(]\\s*", "(");
methodSignature = methodSignature.replaceAll("\\s*[)]\\s*", ")");
methodSignature = methodSignature.replaceAll("\\s*[,]\\s*", ",");
methodSignature = methodSignature.replaceAll("\\s+", " ");
source =source.replaceAll("\\s*[(]\\s*", "(");
source = source.replaceAll("\\s*[)]\\s*", ")");
source = source.replaceAll("\\s*[,]\\s*", ",");
source = source.replaceAll("\\s+", " ");
if(!source.contains(methodSignature)) return null;
// trimming all text b4 method signature
source = source.substring(source.indexOf(methodSignature));
//getting last index, a methods ends when there are matching pairs of these {}
int lastIndex = 0;
int rightBraceCount = 0;
int leftBraceCount = 0;
char [] remainingSource = source.toCharArray();
for (int i = 0; i < remainingSource.length ; i++
) {
if(remainingSource[i] == '}'){
rightBraceCount++;
if(rightBraceCount == leftBraceCount){
lastIndex = (i + 1);
break;
}
}else if(remainingSource[i] == '{'){
leftBraceCount++;
}
}
return source.substring(0 ,lastIndex);
}
Example usage (getTheCode methods is static and in a class called GetTheCode):
public static void main(String... s) throws FileNotFoundException {
System.out.println(GetTheCode.getTheCode("Main", "private static void shoutOut()"));
System.out.println(GetTheCode.getTheCode("Main", "private static void shoutOut(String word)"));
}
Output:
private static void shoutOut(){ // nothing to here }
private static void shoutOut(String word){ // nothing to here }
NB: When starting your new activity create a method eg
private void myStartActivty(){
Intent intent = new Intent(MyActivity.this, AnotherActivity.class);
startActivity(intent);
}
Then in your onClick:
#Override
public void onClick(View v) {
myStartActivity();
myTextView.setText(GetTheCode.getTheCode("MyActivity","private void myStartActivity()"));
}
Update: Ported the Code for android:
import android.content.Context;
import java.io.IOException;
import java.util.Scanner;
public class GetTheCode {
static String getTheCode(Context context, String classname , String methodSignature ) {
Scanner scanner = null;
String source = "";
try {
scanner = new Scanner(context.getAssets().open(classname+".java"));
while(scanner.hasNext()) {
source += " "+ scanner.next();
}
} catch (IOException e) {
e.printStackTrace();
return null;
}
scanner.close();
// extract code using the method signature
methodSignature = methodSignature.trim();
source = source.trim();
//appending { to differentiate from argument as it can be matched also if in the same file
methodSignature = methodSignature+"{";
//making sure we find what we are looking for
methodSignature = methodSignature.replaceAll("\\s*[(]\\s*", "(");
methodSignature = methodSignature.replaceAll("\\s*[)]\\s*", ")");
methodSignature = methodSignature.replaceAll("\\s*[,]\\s*", ",");
methodSignature = methodSignature.replaceAll("\\s+", " ");
source =source.replaceAll("\\s*[(]\\s*", "(");
source = source.replaceAll("\\s*[)]\\s*", ")");
source = source.replaceAll("\\s*[,]\\s*", ",");
source = source.replaceAll("\\s+", " ");
if(!source.contains(methodSignature)) return null;
// trimming all text b4 method signature
source = source.substring(source.indexOf(methodSignature));
//getting last index, a methods ends when there are matching pairs of these {}
int lastIndex = 0;
int rightBraceCount = 0;
int leftBraceCount = 0;
char [] remainingSource = source.toCharArray();
for (int i = 0; i < remainingSource.length ; i++
) {
if(remainingSource[i] == '}'){
rightBraceCount++;
if(rightBraceCount == leftBraceCount){
lastIndex = (i + 1);
break;
}
}else if(remainingSource[i] == '{'){
leftBraceCount++;
}
}
return source.substring(0,lastIndex);
}
}
Usage:
// the method now takes in context as the first parameter, the line below was in an Activity
Log.d("tag",GetTheCode.getTheCode(this,"MapsActivity","protected void onCreate(Bundle savedInstanceState)"));

Let's start with a broader overview of the problem:
Display App code
Press X button
Open new activity with a textview which displays the method
The goal is to do the following:
Viewing app method by extracting it and then building & running it.
There are some methods we can use to run Java/Android code dynamically. The way I would personally do it is DexClassLoader and with Reflection.
If you need more details, let me know. Here is what it'd do though:
View app method
Upon pressing X, launch intent with extra to new Activity
Parse and compile code dynamically and then run it with DexClassLoader and Reflection
Sources:
Sample file loading Java method from TerminalIDE Android App
Android Library I made for Auto-Updating Android Applications without needing the Play Store on non-root devices

Phonegap/Cordova - download jpg to local FS on Windows Phone 8/8.1

I have been trying to download an image from an url to local file system using cordova 3.8 on Windows Phone.
I want to store pictures and be able to use them in the HTML view.
I am using the file transfer and the file system plugins :
https://github.com/apache/cordova-plugin-file-transfer
http://docs.phonegap.com/en/edge/cordova_file_file.md.html
I have been playing around with both, but without success. I think the problem comes from the target file URI, as I have not found any way of getting the download folder path.
I can easily read and write text files using the examples in the cordova-file plugin's documentation, but I do not find anything on how to get the directory's path in order to pass it to the file transfer plugin.
Any idea ? I am testing on WP8.

You can make your own plugin(I can explain how if needed) and use MediaLibrary.SavePicture method. Put this in your plugin class:
public static byte[] ReadFully(Stream input)
{
byte[] buffer = new byte[16 * 1024];
using (MemoryStream ms = new MemoryStream())
{
int read;
while ((read = input.Read(buffer, 0, buffer.Length)) > 0)
{
ms.Write(buffer, 0, read);
}
return ms.ToArray();
}
}
public void SavePicture(string options)
{
string[] optString = getOptionStrings(options);
string url = optString[0];
string callbackId = optString[1];
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
request.BeginGetResponse(new AsyncCallback((result) =>
{
try
{
HttpWebResponse response = (HttpWebResponse)request.EndGetResponse(result);
byte[] content = ReadFully(response.GetResponseStream());
MediaLibrary lib = new MediaLibrary();
lib.SavePicture("Test Picture", content);
DispatchCommandResult(new PluginResult(PluginResult.Status.OK), callbackId);
}
catch (Exception e)
{
DispatchCommandResult(new PluginResult(PluginResult.Status.ERROR, e), callbackId);
}
}), null);
}
And call it like this:
cordova.exec(function (result) {
// success
}, function (e) {
// error
}, 'YourPluginClass', 'SavePicture', [yourUrl]);
NOTE: You must have ID_CAP_MEDIALIB_PHOTO capability checked in the manifest.

Video processing on android, how to write MPEG4 data into a MP4 file?

How to write (wrap) MPEG4 data into a MP4 file in android?
I am doing some kind video processing on android platform, but I don't know how to write the processed data (encoded in some kind standard, like MPEG4) back into video file like mp4. I think it is best to use API to do this, but I can't find the needed API.
Is there anyone have any ideas?

mp4parser can work only with fully created frame streams, u cant write frame by frame with it. Correct me if im wrong
H264TrackImpl h264Track = new H264TrackImpl(new BufferedInputStream(some input stream here));
Movie m = new Movie();
IsoFile out = new DefaultMp4Builder().build(m);
File file = new File("/sdcard/encoded.mp4");
FileOutputStream fos = new FileOutputStream(file);
out.getBox(fos.getChannel());
fos.close();
Now we need to know how to write frame by frame there.

OpenCV might be a little too much for the job, but I can't think of anything easier. OpenCV is a computer vision library that offers an API for C, C++ and Python.
Since you are using Android, you'll have to download a Java wrapper for OpenCV named JavaCV, and it's a 3rd party API. I wrote a small post with instructions to install OpenCV/JavaCV on Windows and use it with Netbeans, but at the end you'll have to search for a tutorial that shows how to install OpenCV/JavaCV for the Android platform.
This is a C++ example that shows how to open an input video and copy the frames to an output file. But since you are using Android an example using JavaCV is better, so the following code copies frames from an input video and writes it to an output file named out.mp4:
package opencv_videowriter;
import static com.googlecode.javacv.cpp.opencv_core.*;
import static com.googlecode.javacv.cpp.opencv_imgproc.*;
import static com.googlecode.javacv.cpp.opencv_highgui.*;
public class OpenCV_videowriter
{
public static void main(String[] args)
{
CvCapture capture = cvCreateFileCapture("cleanfish47.mp4");
if (capture == null)
{
System.out.println("!!! Failed cvCreateFileCapture");
return;
}
int fourcc_code = (int)cvGetCaptureProperty(capture, CV_CAP_PROP_FOURCC);
double fps = cvGetCaptureProperty(capture, CV_CAP_PROP_FPS);
int w = (int)cvGetCaptureProperty(capture, CV_CAP_PROP_FRAME_WIDTH);
int h = (int)cvGetCaptureProperty(capture, CV_CAP_PROP_FRAME_HEIGHT);
CvVideoWriter writer = cvCreateVideoWriter("out.mp4", // filename
fourcc_code, // video codec
fps, // fps
cvSize(w, h), // video dimensions
1); // is colored
if (writer == null)
{
System.out.println("!!! Failed cvCreateVideoWriter");
return;
}
IplImage captured_frame = null;
while (true)
{
// Retrieve frame from the input file
captured_frame = cvQueryFrame(capture);
if (captured_frame == null)
{
System.out.println("!!! Failed cvQueryFrame");
break;
}
// TODO: write code to process the captured frame (if needed)
// Store frame in output file
if (cvWriteFrame(writer, captured_frame) == 0)
{
System.out.println("!!! Failed cvWriteFrame");
break;
}
}
cvReleaseCapture(capture);
cvReleaseVideoWriter(writer);
}
}
Note: frames in OpenCV store pixels in the BGR order.

Your question doesn't make 100% sense. MPEG-4 is a family of specification (all ISO/IEC 14496-*) and MP4 is a the file format that is specified in ISO/IEC 14496-14.
If you want to create an MP4 file from a raw AAC and/or H264 stream I would suggest using the mp4parser library. There is an example that shows how to mux AAC and H264 into an MP4 file.

// Full working solution:
// 1. Add to app/build.gradle -> implementation 'com.googlecode.mp4parser:isoparser:1.1.22'
// 2. Add to your code:
try {
File mpegFile = new File(); // ... your mpeg file ;
File mp4file = new File(); // ... you mp4 file;
DataSource channel = new FileDataSourceImpl(mpegFile);
IsoFile isoFile = new IsoFile(channel);
List<TrackBox> trackBoxes = isoFile.getMovieBox().getBoxes(TrackBox.class);
Movie movie = new Movie();
for (TrackBox trackBox : trackBoxes) {
movie.addTrack(new Mp4TrackImpl(channel.toString()
+ "[" + trackBox.getTrackHeaderBox().getTrackId() + "]", trackBox));
}
movie.setMatrix(isoFile.getMovieBox().getMovieHeaderBox().getMatrix());
Container out = new DefaultMp4Builder().build(movie);
FileChannel fc = new FileOutputStream(mp4file).getChannel();
out.writeContainer(fc);
fc.close();
isoFile.close();
channel.close();
Log.d("TEST", "file mpeg " + mpegFile.getPath() + " was changed to " + mp4file.getPath());
// mpegFile.delete(); // if you wish!
} catch (Exception e) {
e.printStackTrace();
}
// It's all! Happy coding =)