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Use Java or other languages in a Flutter Application

Since I got no answer and not much feedback on this question: Android Flutter Analyze Audio Waveform
and found nothing online about what I'm looking for, I'll simply ask a broader question, since a comment on that answer told me to use native code and use a platform channel to connect it to flutter but when I asked some clarifications I got nothing.
So my question is If I can do operations in Java (which has been around since a much longer time, and thus has a way bigger documentation), and then use the outcome in Flutter.
More precisely, could I do these things in Java and Flutter:
1) Analyse Audio waveform and find peak points in specific frequencies, and use the timestamp to display them in flutter;
Edit 1:
What Are Peak Points?
This Is the waveform of different frequencies ranges (The Orange one is bass (80-255Hz)), and the Points circled in black are Peak Points. I should analyze the audio specter of a song and Find the peak points in certain frequencies. Then When I Find the Peaks I need to save the timestamps, for example, 16 seconds in and so on.
2) Edit 2:
I need to Edit some photos in a video, like a video collage, for which each frame of a 30 or 60fps video is an image.
3) Edit 3:
I need to add basic frame specific effects to the video, for example a blur that will change frame to frame, or a glare.
4) Adding Music to that video and save it to an mp4 or avi or any format.
5) Edit 4: Most Important thing, I don't want to this all in real time, but more like an After Effect like Render process, in which all the frames are rendered together. The Only thing that would be nice is a sort of progress bar telling the user that the Render is at frame, for example, 200 of 300, but I don't want to display any of the frames or the video, just to render it in background and then save it to an mp4 video that can be viewed after.
As You can see it's a difficult process to do in a language to which you hardly find a tutorial on how to play music due to its early state. But Uis and some other things in flutter are way easier to do and Flutter is also Multi-Platform. So I prefer to stick to Flutter language.
Edit 5:
I took a look at Qt and JUCE, and found out that Qt seems a valid alternative but it seems for what understood more like a "closed" system, I mean, for example I looked the multimedia library but for what I've understood, you can do basic stuff, for example play a video, but not collage frames and save it. (Don't know if I explained myself well). JUCE On the other side, looks better but it seems more for PC audio VST than for mobile applications including video rendering. And another thing is that these two are not free and open source like Flutter is.
Then There is Kivy, which could and could not be the best, because it is a Python port for Mobile Devices and I have a lot of experience with Python And I think it's one of the easier language to learn, but on the other side, it hasn't got that much UI power. and as you mentioned there could be problem using libraries on Android.
You stated I could use C++ or Java With Flutter, but with C++ you told that it's a difficult process. So My question turned out to be Could I write the process in java with a Normal Android Application And Then in some way use the functions in a Flutter App?
Edit 6:
I found a possivle alternative:
Kha (http://kha.tech/). But again found nothing on how to use it with Flutter. Could it be a good Idea?
I'm asking more of a confirmation on if I could use Java or any other language to do what I need in a Flutter Application. And If yes if it's complicated or not that much. (I'm a beginner sorta). But Some tutorial or links to kickstart the code would be helpful aswell!

Flutter at this time is great for building UIs but as you've mentioned, it doesn't have a lot of power or compatibility with libraries yet. A good part of the reason for that is that it doesn't have easy integration with c++, but I won't get into that now.
What you're asking is most likely possible but it's not going to be simple at all to do. First, it sounds like you're wanting to pull particular frames from a video, and display them - that's going to be an additional complication. And don't forget that on a mobile device you have somewhat limited processing power - things will have to be very asynchronous which can actually cause problems for flutter unless you're careful.
As to your points:
This is a very general ask. I'd advise looking up android audio processing libraries. I'm almost sure it's possible, but SO questions are not meant for asking advise on which framework to use. Try https://softwarerecs.stackexchange.com/.
Once again, fairly general and a bit unclear about what you're asking... Try sofwarerecs. I assume you're wanting to take several frames and make them into a video?
Some of those effects (i.e. zoom) you could definitely do with flutter using a Transform. But that would just be while playing in flutter rather then adding to the video files themselves. To do that, you'll have to use the video library in android/java code.
Once again, the video library should do this.
This should also be part of the video library.
I do know of one audio/video library off the top of my head called Processing that may do what you need, but not for sure. It does have an android sdk though. OpenCV would be another but only for video/image processing and I haven't used it directly with Java so I'm not sure how easy it is to use.
For how you'd actually go about implementing this along with flutter... you're going to need to use Platform Channels. I mentioned them in the comment to your other answer but figured you could look that up yourself. The documentation does do a much better job of explaining how that works and how to set it up than I can. But the TLDR is that essentially, what they allow you to do is to send serialized data from native code (java/kotlin/swift etc) to flutter code (dart) and vice-versa, which gets translated into similar data structures in the target language. You can set up various 'channels' upon which the data flows, and within those channels set up 'methods' which get called at either end, or simply send events back and forth.
The complication I mentioned at the beginning is that sending images back and forth across the channels between flutter and dart isn't all that optimal. You most likely won't get a smooth 24/30/60fps of images being sent from java to dart, and it might slow down the rest of the flutter ui significantly. So what you'll want to use for the actual viewport is instead a Texture, which simply displays data from the android side. You'll have to figure out how to write to a texture from android yourself, but there's lots of information available for that. Controls, the visualization of the audio, etc can be done directly in flutter with data that is retrieved from native.
What you'll have is essentially a remote control written in dart/flutter, which sends various commands to a audio/video processing library & wrapper code in Java.
If all that sounds complicated, that's because it is. And as much as flutter is very nice to build UIs in, I have doubts as to whether it's going to be worth the extra complications if you're only targeting android.
Not really related to the answer but rather some friendly advice:
There is one other thing I'll mention - I don't know your level of proficiency with programming and with different languages, but video/audio processing and such are generally not done in java but rather in actual native code (i.e. c/c++). As such, there are actually two levels of abstraction you're going to have to be dealing with here (to some degree as it will probably be abstracted somewhat or a lot depending on the library you're using) - c/c++ to java and java to dart.
You may want to cut out the middlemen and work more directly with native - in that case I'd recommend at least taking a look at Qt or JUCE as they may be more suitable than flutter for your particular use case. There's also Kivy (uses python) which may work well as there's a ton of image/video/audio processing libraries for Python somehow... although they may not all work on android and still have the c++ => python translation to some degree. You'll have to look into licensing etc though - Qt has a broad enough OS licence for most android apps, but JUCE you'd have to pay for unless you're doing open source. I'd have to recommend Qt slightly more than the others as it actually has native decoding of video frames etc, although you'd probably want to incorporate OpenCV or something for the more complicated effects you are talking about. But it would probably be on the same level of complicated as simply writing in java code, but with a slightly different UI style & easier integration with c++ libraries.

Possibly non-intrusive method to change complete android application code with a library

I'm having quite tough problem while developing a testing framework for android apps. The text got a bit long so the actual question is in bold for those that don't want to read the context.
Basically, what I'd like to achieve right now is to trace user activity while he's using the application as one of the features. There's my app that manages context data all the time and developer's app - the one being tested. My idea to do this was to get coordinates where user touched the screen along with taking a screenshot simultaneously. Then I'd use the coordinates to mark the spot on the screenshot to get the idea of what user was doing the whole time with the app. Take hints on user experience and trace crashes.
Non-system apps cannot take a screenshot for security reasons, but application itself can take a screenshot of its Activities without much trouble for non-rooted users, e.g. like here. My only hope here is to interfere with developers' code to implement the functionality of doing so while my testing app is running. Each Activity then would have to extend my overridden Activity instead of regular one, implement an interface, implement broadcast receiver etc.
I am going to write a library for developer who would like his app to be tested with my framework. I'd like it to do the job for me and be as non-intrusive as it's possible for him to use. How to achieve that the best way?
Ideal case would assume linking the library to project with maybe a small addition in manifest that'd get the job done and after just unlinking, removing that bit of xml in manifest for production.
That's an open question. I don't expect any bits of code, but some nifty Java trick, Android OS functionality or even completely other approach that'd solve my problem
I tried to be as clear as possible with the question, but that's a quite tough matter for me to describe so that could have turned out contrary. Don't hesitate to ask me for more details, to speak my mind more clearly or even rewrite the question. Thank you all very much for help!

Continuous speech recognition while singing?

As part of my application I'm looking to add speech recognition, but not really in the traditional sense. I have a bunch of lyrics (divided into verses) that are sung by someone, and the idea is to find what verse is currently being sung so it can be displayed on screen.
I've played around with sphinx and got some basic examples set up and working, but while there seems to be plenty of documentation around on registering spoken text where you can wait for a delay then process the result, I can't find much on the idea of recognising sentences continuously. This is of course before I get to the part where the words are being sung and not spoken!
Has anyone got any experience with this, and if so is there anywhere that would provide a good starting point? Or is what I'm trying to achieve way too ambitious with sphinx and is it never really going to work properly? I'm open to looking at other libraries but they must be free, and sphinx was the most widely talked about one I could dig up.

It's perfectly possible to recognize speech as soon as it's pronounced with a little delay. Moreover if you more or less understand what do you expect to get. This is called "partial result" and is available in all CMUSphinx decoders through API. Basically you can retrieve hypothesis in process.
There is a little issue to consider on how to stabilize this result (how to extract the stable part of it) but this technique is called backtracking and could be easily implemented
For singing, given the music can be filtered out it's also doable.

is there any inbuilt function for image recognition

i want to use a function for image recognition
i dont want to make an algorithm.
please suggest me a function where i could compare two images and tell whether these images belong to the same object.
please help me!.

Arbitrary image recognition is something that computers can't yet do (even for supercomputers). However, Google Goggles comes close, being able to recognize a wide range of objects. Read its limitations, and see if it suits your purpose.

Yes. There are definitely ways to do this but they all depend on what you are trying to do. If you are more specific about what you want to compare then it will be easier to give a more thorough answer.
There are some excellent libraries out there but it will require some effort on your part to learn and understand how to use them and how to use them on the iPhone.
The most famous algorithms so assist in finding images inside other images are called SIFT and SURF. Unfortunately both are patented and cannot be used commercially in an application.
Consider using OpenCV for most of your image operations.
Or you could use OpenFrameworks (google has tagged it as a phishing site for some reason, im sure theyll fix that soon)
You might also consider VXL which has started to become more popular.
Good luck!

Whats the best way to start programming for my non-smartphone?

I have a general old-fashioned phone that has no special app system and uses Java (I assume ME) for the few applications you can use on it.
This is still a decent userbase and I'd like to start programming for this type of phone. I already know basic Java theory and syntax, so.. where do I get started for programming for non-smartphones?

Best programming environment for Java ME IMO is Eclipse with EclipseME. Includes lots of built-in stuff about packaging your midlets etc. The SonyEricsson wireless toolkit is great for PC-based testing and debugging, but don't forget on-device testing!
If you don't know much about Java ME's lifecycle, then get reading as widely as you can, and try lots and lots of examples. Start with the JSR-118 (MIDP2) javadocs; you'll want these open on your desktop at all times while coding.
Don't waste too much time with the form-based user-interface; I recommend either rolling your own using Canvas, or read about LWUIT.
You can do all sorts in Java ME and target a very broad range of handsets. HTTP capability is guaranteed, so you can hook up to a public web service, or create your own using something like Google Appengine.
Finally, you can release your app very easily on somewhere like Get Jar. Don't be put off by those who say "no owners of Java ME handsets want apps", you'll find the most popular user bases on this site will be users in countries such as India and Indonesia.
Good luck!

I would start with a book on J2ME and work from there.
Try Beginning J2ME: From Novice to Professional.
You could also download the J2ME SDK and play around with the example they give.
For tutorials have a look at the stackoverflow question https://stackoverflow.com/questions/584923/do-you-know-a-good-j2me-tutorial as mention in my comment.

I started with writing simple Flashlight application (choose how much seconds screen will remain lit) in NetBeans ME. And other app which I mange was Countdown with some graphics and sound. After that I found limitations too much annoying and now I'm waiting for my Android phone.
in short:
If you want to try it out - you don't need to buy books. There are plenty of tutorials around.
But, if you want to start deep development - don't waste time.