QtGstreamer fails creating pipeline after QGst::cleanup()

[Karl Phillip]

Hi all,

I spent a lot of time to pinpoint this problem and I wonder if it's a bug
of QtGstreamer or not.
If it's not, we seriously need to make this thing more clear on the
documentation and prevent others from making the same mistake as I did.

I wrote a VideoPlayer class to deal with video files using QtGstreamer
under the hood. I was able to instantiate a VideoPlayer object and display
the video with no problems.
Then, I tried to destroy the current player and instantiate a new one
(within the same thread) to watch another video. That's when it happend:
the second object failed to create it's pipeline.

Hours of investigation went by until I found the source of the problem: the
constructor of VideoPlayer initialized the library through "QGst::init();"
and the destructor did the opposite with "QGst::cleanup();".
It was my understanding that after a
cleanup()<http://gstreamer.freedesktop.org/data/doc/gstreamer/head/qt-gstreamer/html/namespaceQGst.html#af854931adda54e40b759bf4f736f1cbb>operation,
a call to init() would restore things back to it's operational
state, but so it happens that cleanup() makes it impossible.

What is also strange is that calling QGst::init() after a cleanup() doesn't
return any errors nor throw exceptions, which I think it should, since you
can't use the library to create a new pipeline rendering it pretty much
useless.

I wrote a small demo to reproduce this behavior:

#include <QObject>
#include <QGst/Init>
#include <QGst/Pipeline>
#include <QGst/Element>

int main()
{

    qDebug() << "#1 call QGst::init()";
    QGst::init();

    QGst::PipelinePtr _pipeline = QGst::Pipeline::create();
    if (!_pipeline)
    {
        qDebug() << "#1 Failed creating pipeline !!!";
        return -1;
    }

    qDebug() << "#1 Setting pipeline to Playing";
    _pipeline->setState(QGst::StatePlaying);

    qDebug() << "#1 Setting pipeline to Null";
    _pipeline->setState(QGst::StateNull);

    qDebug() << "#1 call pipeline.clear()";
    _pipeline.clear();

    qDebug() << "#1 call QGst::cleanup()";
    QGst::cleanup();

    qDebug() << "\n* Press <enter> to restart the pipeline setup";
    getchar();

    qDebug() << "#2 call QGst::init()";
    QGst::init();
    _pipeline = QGst::Pipeline::create();
    if (!_pipeline)
    {
        qDebug() << "#2 Failed creating pipeline !!!";
        return -1;
    }

    return 0;
}


Thanks!
--
Karl Phillip
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