Display Gstreamer video on Android

SGaist

Hi and welcome to devnet,

@LuJoRi Indeed it wasn't mad causeless because Qt uses as much as possible native frameworks.

If I understand you correctly you successfully used GStreamer on Android with Qt to do video rendering ?

don-prog

@SGaist ok, I downloaded QtMultimedia source and found that block:

android {
   SUBDIRS += android opensles
}

What I should to do next? Just add /home/user/Downloads/gstreamer-1.0-android-armv7-1.8.0 in the end?

LuJoRi

@SGaist, yes exactly! It was one of my core topics of my master thesis which I'll finally release after the weekend :)
@don-prog, @SGaist, are you interested in my solution? It will take some time for me to explain you in english since it isn't my first language (it's german).

A few quick hints:

you should look for a surface of the Java/Android-API and get the pointer on it via ANativeWindow_fromSurface(...) --> so you can handle the surface's display area within C++/Qt
with this pointer you are able to use the standard GStreamer way to render a video in a specific display area.
Your function call was:
gst_video_overlay_set_window_handle(GST_VIDEO_OVERLAY(video_sink), this->ui->playback_widget->winId());
--> you have to use the pointer on the native window instead of winId()...the winId() function returns useful values on Linux but not on Android!

SGaist

@don-prog Sure thing !

That may avoid @don-prog some pain.

@don-prog you would need to add gstreamer to SUBDIRS. It's the name of the plugin dir. However, AFAIK, that plugin uses pkg-config to find gstreamer's library/includes so it may be problematic. You would have to put the the paths yourself in there.

don-prog

@LuJoRi many thanks for your support and experience! I am very interested in your solution because I already thought about some way like yours, but I have some misunderstandings:
How can I use ANativeWindow_fromSurface() from Qt and with which arguments?

LuJoRi

@don-prog you have to do function calls from C++/Qt to Java/Android-API via JNI. Look for QAndroidJniObject (http://doc.qt.io/qt-5/qandroidjniobject.html) --> that's a way to create instances of classes of the Java/Android-API. Furthermore you can call their methods - for example via

 QAndroidJniObject::callObjectMethod(const char *methodName, const char *signature, ... )

That means that you first have to manage a Java surface object will be created. You do this via JNI. Then you can put this one as an argument to the ANativeWindow_fromSurface function.

don-prog

@LuJoRi understood, via JNI :)
But I still don't understand what I need to put in the ANativeWindow_fromSurface() function as first(JNIEnv * env) and second(jobject surface) argument?

LuJoRi

@don-prog
The first agrument requires something like a pointer on the Java environment which is needed because on Android even a Qt application is based on a JVM respectively ART (Android Runtime).
The second one is the C++/Qt handle of the Java surface. Once you've retrieved it after your JNI calls, you can cast it to jobject type and then put it to the ANativeWindow_fromSurface function :)

Unfortunately I'm short of time the next days (till sunday). Regardless I'd really like to help you! Feel free to ask if there are any questions :)

don-prog

@LuJoRi excuse for troubling! And what is the second argument in Qt exactly? I think it's not qwidget->winId(), so what?

LuJoRi

@don-prog
Sorry for the late response!

No, forget winId() respectively the returned WId on Android for your purposes :)

The second argument for ANativeWindow_fromSurface is the pure JNI object of a Java surface which you'll retrieve from the Java/Android world! The ANativeWindow_fromSurface function will return a pointer to the display which is managed by the Java surface. With this pointer you are able to access this display area within C++/Qt...since Qt's winId() function doesn't return proper values on Android the pointer you retrieve via ANativeWindow_fromSurface will be something like a replacement for the "missing" WId.

Are you familiar with the Android-API and how to get a surface in standard Android way? --> you need a SurfaceView and with its SurfaceHolder you can get access to the corresponding Surface. Since you are working with Qt, you have to try doing this stuff via JNI respectively QAndroidJNIObject :) When you get the JNI object of a Java surface this will be your second argument for the function ANativeWindow_fromSurface.

For my thesis I've created a clear view of the whole procedure...I hope you understand I have first to go in conversation with my professor before I'll post things (diagrams, figures) which I created for my thesis. These days I'm doing the final cut for my thesis document which I'll deliver after the weekend. I'd like to do the delivery of the thesis first and then help you out with detailed description :) I hope it's okay for you?

Nevertheless I'll try to answer your questions in the meantime :)

Lukas

don-prog

@LuJoRi of course, it's absolutely ok! I'm student too and I understand you fully :)
I just have two questions:

Can I display video in NOT full screen(display video in some child widget of my application)? Or I can display video ONLY in full screen? Of course I mean via Qt and GStreamer.
How can I get SurfaceView of the widget(if I can display video in not full screen) or of the full window(if I can display video only in full screen)?
Regards.

LuJoRi

Okay, good to know :)

@don-prog said:

Can I display video in NOT full screen(display video in some child widget of my application)? Or I can display video ONLY in full screen? Of course I mean via Qt and GStreamer.

How can I get SurfaceView of the widget(if I can display video in not full screen) or of the full window(if I can display video only in full screen)?
Regards.

Yes, you can display a video wherever you want and in every size you want
In fact the surface isn't part of your Qt-GUI --> you'll get something like a "mixed GUI" with a Qt part and a Java part. All of your GUI will be drawn by Qt except the part where your video will be rendered because this will happen inside the display area which is hold by the Java surface. If you create a Java surface with size 100x100 px via JNI there will be an area with this size ontop of your Qt-GUI which has nothing to do with Qt itself. To describe how you can get it is a longer term which I'll show you after my delivery :))

don-prog

@LuJoRi understood, that is a very good news! I will wait when you can share your information about this subject. By the way, good luck :)

chaudhry

@LuJoRi I also have exactly the same requirement that is to render video inside a Qt application on Android using gstreamer. It would be really helpful if you could explain the steps for building gstreamer for a qt application with Android as a target.

LuJoRi

Hey guys ... my thesis is done :)

I will explain you the procedure step by step this evening or tomorrow in the afternoon.

Greetz Lukas

LuJoRi

A rough overview to get an idea how it works:

First you should take a general look on the dependencies between SurfaceView, SurfaceHolder, Surface in the documentation of the Android API. This is essential to understand what you have to do to get access to an Android Surface.

If you know how it works you can do the creation of the needed objects (of SurfaceView, SurfaceHolder, ...) via JNI calls respective QAndroidJniObject! For all of this you should create a QRunnable --> in its run()-method you do the creation of the objects you need --> QAndroidJniObject is your friend here :)

void QRunnable::run()
{
     //create your needed objects of SurfaceView, SurfaceHolder, ... via QAndroidJniObject
}

Later you have to take care about executing this run()-method in context of the Android UI thread! The created instance of Surface is your second parameter for the ANativeWindow_fromSurface function :)

don-prog

@LuJoRi hello!
I'm very sorry for the so late reply, but I just had some urgent problems, and I had to leave this forum and work with another things.
I see that you shared your advice and sample for this issue as you promised.
So I want to thank you for this!
Unfortunately, I had to do other things, but I think that you helped other users (including chaudhry) to solve this not simple task! :)
Sorry and thank you one more time!