Display Gstreamer video on Android

don-prog

@SGaist ok, thanks. And what is the difference between QtGstreamer module and Qt's GStreamer backend?

SGaist

The QtGstreamer module is on a lower-level. It essentially provides you a nice Qt API to build your GStreamer pipelines and a set of video sync for QtWidgets and QtQuick.

don-prog

@SGaist as I understand QtGstreamer will works for my issue too, so what is more preferable? How can I use QtGstreamer? And is it cross-platform? Thanks!

SGaist

It should run on the same platforms as Qt as long as you can satisfy its dependencies.

I'd first try to build the backend. It will likely be less work.

don-prog

@SGaist understood. Thanks for the explanations. About backend:
I need download GStreamer for Android(this I already did, right?), create plugins.pro file in the my project(I don't know even what is it, but I will read) and add GStreamer dir to the list in the android scope(don't heard about this too). Is it all what I need?

SGaist

No, you have to build the plugin from the sources and then install them

don-prog

@SGaist can you share the link which describes what I need to do? Or some additional reading? I'm sorry but I really don't understand a lot of things. Where I need to set a plugins.pro? What I need to set within it? About which plugin are you said? How and where I need to install it? How connect GStreamer to all these things?

SGaist

You don't need to create any file. You have to first get the sources of the QtMultimedia module.

There you'll find the plugins folder with the matching plugins.pro file

LuJoRi

Hi don-prog!

I've had the same issue as you...displaying a GStreamer video on Android within a Qt application!
It was a hard way to find out how to get it alltogether work and it took me a long time! I wasn't able to find really useful hints about this issue.

First I also tried it with QtGStreamer, but I didn't get it work for Android. After trying and trying and trying (...) I decided to look for another way to go. By the way - for Linux the QtGStreamer worked like a charm.

As you can see at this link (https://wiki.qt.io/Qt_5.5.0_Multimedia_Backends) the multimedia backend of Qt uses different multimedia frameworks on different platforms --> GStreamer is only used for Linux and I think this decision wasn't made causeless! I don't think it will be so easy to get the Qt's GStreamer-Backend to work for Android since a Qt application for Android comes with partial other characteristics than a Qt application for Linux. That's based in the differences between the dissimilar windowing-systems of Android and Desktop-Linux.

If you display some patience I'll show you how I did it?

Greetz, Lukas

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.