I am thinking about using hardware encoding on my Nexus Tablet, since I need to use some video algorithm, I want to make it C.
There is a native-media sample in Google NDK which support native use of OMX to do the decode job. But it seems that it doesn't support encode yet. Now we have the MediaCodec API, which can provide the hardware encode. I check the java file, it seems that most of it function is written in C. So I am wondering if this is possible:
1)find the corresponding C files
2)compile these C file into .so file
3)write a .cpp file according to the MediaCodec.java file, this .cpp file will call the functions in the .so file and perform the similar function as MediaCodec.java.
Then I can do the encode in C.
Is that right? And is that possible? If that possible, do i need to modify the system on my tablet?
Thank you!
Related
I am new to android. I have two files of same length, One is audio file and one is video file with no audio. I want to make a video with audio by combining these two files. Help me to achieve this task.
I assume you have native Android app and familiarity with Java (or know porting the code in native C) and are willing to use other open-source classes in your project.
This is what you might give a head-start: Since this project is not actively maintained now, you might have to fork and use their logic into your code.
https://github.com/tqnst/MP4ParserMergeAudioVideo
Another alternative is using ffmpeg port for Android (however I am not sure how this works natively).
https://github.com/WritingMinds/ffmpeg-android-java
I am working on a matlab project where I add effects to audio files (mp3, wav). Therefore, I load the files into arrays using the matlab function audioread(..).
Now, I want to export this to Android. I read that the best way is to use the Matlab Coder to export the matlab code to C/C++ (or Java) and then export it into android (more or less).
However, the function call audioplayer (and play) are Unsupported (that's what the code generation readiness issues says).
What can I do ? One idea was to play the sounds directly using c++ code (so after the code generation). But how to play sounds from arrays using c++ ?
Or if you guys have others ideas without touching c++ codes (so fixing the problem directly in matlab), I would be glad to hear it !
Thanks and have a good day !
Typically what I recommend in cases like this is to factor your code in two pieces:
The part that does the audio file I/O and audio playing (namely the OS-specific part)
The computational kernel for which you will generate code using MATLAB Coder. This piece usually takes numeric arrays representing the image or audio data as arguments.
I've used this approach to leverage MATLAB Coder generated code to do image filtering on Android.
To do part (1), as Navan says, you'll need to use Android APIs to read in audio files, write data back to files, and to play them as desired. Note, I haven't done extensive Android development, so doing these tasks may take some research or be difficult.
Once you have the data in a format suitable for the function(s) in (2), likely a numeric array, then you can call your generated code using JNI to add the desired effects. The generated code would return the data back to the Java code and you can then encode it, play it, or do as you please with it using the Android APIs.
Playing audio normally uses platform dependent libraries. In DSP System toolbox, there is an audio player object called dsp.AudioPlayer which supports C code generation. But I believe this uses platform dependent libraries in the generated code and it will not be straight forward to make it work in Android. You will be better off finding an audio player library for Android and hooking that in manually after generating code.
I am trying to build an video recording system on Android 4.2.2, I've done the encoding part, which is using OMX. Now I am working on the Muxer part, since the code stream of the video can be a little different if I use FFMpeg, so I wish to use the exact same Muxer tool of the original system.
So I want to extract the Muxer part of StagefrightRecorder, compile it into a .so file, and then call it via JNI in my application. But there are a lot of stuffs in StagefrightRecorder, I am confused.
Can this way work? Can I just extract the code relevant to MPEG4Writer? Can anyone give me any instructions?
Thanks!
If you are compiling within the context of the framework, you could simply include the relevant header files and create the MPEG4Writer object directly. A very good example for this is the command line utility recordVideo as can be observed from this file.
If you wish to write a separate application, then you need to link with libstagefright.so and include the relevant header files and their path.
Note: If you wish to work with the standard MPEG4Writer, it's source i.e. source of the MPEG4Writer which would be an encoder should be modeled as a MediaSource. The writer pulls the metadata and actual bitstream through the read method and hence, it is recommended to employ a standard built-in object such as OMXCodec or ACodec for the encoder.
I have recently begun using the Android NDK and I have successfully implemented a few simple Android apps. I need to detect objects (squares and rectangles) from an image. My research has shown me that OpenCV is the solution for this. This is the algorithm I use to detect a square from the image.
However, I am unclear as to how should I use the squares.cpp file in my code. The OpenCV samples show how to use the cpp files in JNI format. Do I need to convert the squares.cpp file to JNI or would there be another feasible solution?
Thanks. All suggestions and feedback are welcome.
You don't have to convert the squares.cpp file to JNI.
From your Java code, you will call a JNI function (as I suppose you did in the "few simple Android apps" you have implemented) that will then call the functions in squares.cpp.
In other words, you basically only need one call to a JNI function from Java, and once you are in the C++ code, you can code in C++ as usual.
I have an external compiled static C++ library that I'm using in my android application. This library is reading a file. I want to know if there is a way I can "redirect" the function that's reading the file so that it reads another file.
So if it does:
fopen("myfile.txt", "rb");
I want to intercept it and to do this instead:
fopen("myotherfile.txt", "rb");
In Objective-C I use MethodSwizzling. Is there something similar I can do in C++ or the android NDK?
Short of editing the binary (with uncertain results), your best option is to use a symlink... if you're just doing it for development purposes, you could use adb shell into your test device to create the symlink.
http://developer.android.com/guide/developing/tools/adb.html#issuingcommands
How about contact the author of the library and ask them to introduce a parameter? Having hard-coded file paths is a lousy design anyway, the library will be better off.