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() 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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