Gstreamer with multithread app (Qt)
Matias Hernandez Arellano
msdark at archlinux.cl
Tue Apr 12 15:59:46 PDT 2011
> Why on earth are you using so many threads here. Each queue starts a
> new thread; additionally, appsrc starts a new thread too and maintains
> an internal queue (making the second queue right after it completely
> useless).
The true.. i find/read some example and this work.... but i ever think about this, but "if work don't touch it" ... xD
>>
>> this->pipeline = QGst::Parse::launch(pipe_str).dynamicCast<QGst::Pipeline>();
>> QGlib::connect(this->pipeline->bus(),"message",this,&StreamThread::onBusMessage);
>> this->pipeline->bus()->addSignalWatch();
> This is where the QTimer starts, inside the signal watch. You can see
> the code here [1] if you want. This timer expires every once in a
> while and polls the GstBus for new messages. It's purpose is to
> deliver messages to the main thread. I'm not sure why it shows that
> error message though on the output... I'll check it, it doesn't seem
> normal.
So if i remove this (the connect and addSignalWatch) i don't use QTimer, but i can't get errors messages from the pipeline.
>> void StreamThread::run(){
>> this->exec();
>> }
I modify this to run a infinite loop where i push data into appsrc.
> Why are you setting the pipeline *again* to playing state?
A mistake ... this was for testing purpose ...
>> Mat frame = this->ImageBuffer->getFrame();
>> data = (quint8*)frame.data;
>
> I hope you realize that this statement is void, it copies no actual
> data. You need to copy the data with memcpy() instead.
>
>> QGst::FlowReturn ret = this->m_src.pushBuffer(buffer);
I do this cause i asking in other thread about the use of QGst::Buffer and i get this:
The QGst::Buffer class has a data() method which gives you a pointer
to the allocated buffer. You can use this pointer to write on the
buffer.
Btw, the above line of code looks terribly wrong to me... Here is how
you should use it:
QGst::BufferPtr b = QGst::Buffer::create(size);
quint8 *data = b->data();
//use the data pointer to write.
But i don't know if this is right.. so i try with memcpy. When i testing with C interface of Gstreamer i do this:
memcpy(GST_BUFFER_DATA(buffer),img_data,data_size);
even i use this GST_BUFFER_DATA(buffer) = img_data; GST_BUFFER_SIZE(buffer) = 640*480*3*sizeof(uchar*);
but now i don't know how copy the data into QGst::Buffer... this don't work ...
memcpy(data,frame.data,640*480*3*sizeof(uchar*))
Sorry if my questions are too silly but i'm a newbie with this..
Thanks a lot!!
El 12-04-2011, a las 17:26, George Kiagiadakis escribió:
> Hello,
>
> On Wed, Apr 13, 2011 at 12:34 AM, Matias Hernandez Arellano
> <msdark at archlinux.cl> wrote:
>> (me again)...
>> Well i try it a lot of things and finally i get a proof of concept of the final application semi functional using Qt+OpenCV+QGstreamer ...
>> but.. yet.. i have a problem..
>>
>> Here some snippets of code
>>
>> main.cpp
>> int main(int argc, char *argv[]){
>> QCoreApplication a(argc, argv);
>> QGst::init(&argc,&argv);
>> FrameBuffer *buffer = new FrameBuffer(3);
>> FrameBuffer *buffer2 = new FrameBuffer(3);
>> CaptureThread *capture = new CaptureThread(buffer,0);
>> ProcessingThread *processing = new ProcessingThread(buffer,buffer2,capture->getSourceWidth(),capture->getSourceHeight());
>> StreamThread *stream = new StreamThread(buffer2);
>> QCoreApplication::connect(processing,SIGNAL(newframe()),stream,SLOT(update()),Qt::QueuedConnection);
>> capture->start();
>> processing->start();
>> stream->start();
>> return a.exec();;
>> }
>>
>> buffer and buffer2 are Circular Buffers that hold cv::Mat (OpenCV Images).
>> buffer hold cv::Mat obtained with CaptureThread. ProcessingThread pull images from here.
>> ProcessingThread push images into buffer2 and StreamThread pull images from here.
>>
>> The cycle works good...
>> now the StreamThread
>>
>> StreamThread::StreamThread(FrameBuffer *b, QObject *parent): ImageBuffer(b),QThread(parent){
>> QString pipe_str = QString("appsrc name=\"appsrc\" caps=\"video/x-raw-rgb,width=320,height=240\" ! queue ! videoparse format=14 width=%1 height=%1 ! videorate "
>> " ! videoscale ! video/x-raw-rgb,width=320,height=240 "
>> " ! queue ! ffmpegcolorspace ! jpegenc ! queue "
>> " ! tcpserversink port=5000 ").arg(WIDTH,HEIGHT);
>
> Why on earth are you using so many threads here. Each queue starts a
> new thread; additionally, appsrc starts a new thread too and maintains
> an internal queue (making the second queue right after it completely
> useless).
>
>> this->pipeline = QGst::Parse::launch(pipe_str).dynamicCast<QGst::Pipeline>();
>> QGlib::connect(this->pipeline->bus(),"message",this,&StreamThread::onBusMessage);
>> this->pipeline->bus()->addSignalWatch();
>
> This is where the QTimer starts, inside the signal watch. You can see
> the code here [1] if you want. This timer expires every once in a
> while and polls the GstBus for new messages. It's purpose is to
> deliver messages to the main thread. I'm not sure why it shows that
> error message though on the output... I'll check it, it doesn't seem
> normal.
>
>> this->pipeline->setState(QGst::StatePlaying);
>> this->m_src.setElement(this->pipeline->getElementByName("appsrc"));
>> }
>> void StreamThread::onBusMessage(const QGst::MessagePtr &message){
>> switch (message->type()) {
>> case QGst::MessageEos:
>> quit();
>> break;
>> case QGst::MessageError:
>> qCritical() << message.staticCast<QGst::ErrorMessage>()->error();
>> break;
>> default:
>> break;
>> }
>> }
>> void StreamThread::run(){
>> this->exec();
>> }
>
> I wonder if you understand that this event loop here is completely
> useless. The update() slot will NEVER be called in this thread,
> because this QThread object, being a QObject itself, lives in the main
> thread and all of its slots are called in the context of the main
> thread. So, the whole "StreamThread" could actually be a QObject
> instead of a QThread and still do the same job. Let me add that since
> appsrc itself handles queuing, you don't really need this extra thread
> here.
>
>> //This SLOT fires up when ProcessingThread calls the newImage() SIGNAL ..
>> // this signal ocurrs when a new processing image was push into the buffer
>> void StreamThread::update(){
>> if(!this->m_src.element().isNull()){
>> this->pipeline->setState(QGst::StatePlaying);
>
> Why are you setting the pipeline *again* to playing state?
>
>> QGst::BufferPtr buffer = QGst::Buffer::create(WIDTH*HEIGHT*3*sizeof(quint8*));
>> quint8 *data = buffer->data();
>> Mat frame = this->ImageBuffer->getFrame();
>> data = (quint8*)frame.data;
>
> I hope you realize that this statement is void, it copies no actual
> data. You need to copy the data with memcpy() instead.
>
>> QGst::FlowReturn ret = this->m_src.pushBuffer(buffer);
>
> ...and effectively here you are pushing an empty buffer. No wonder why
> the other end doesn't receive anything.
>
>> if(ret!=QGst::FlowOk){
>> qDebug()<<"Error pushing data";
>> }
>> }
>> }
>> StreamThread::~StreamThread(){
>> this->pipeline->setState(QGst::StateNull);
>> }
>>
>> When i run this app i don't get errors, just this warning (this doesn't show if i don't execute StreamThread)
>> QObject::startTimer: QTimer can only be used with threads started with QThread
>> So i suppose that QGstreamer use QTimer in some hidden part.
>>
>> And... if i try to see the stream using
>> gst-launch tcpclientsrc host=127.0.0.1 port=5000 ! jpegdec ! queue ! video/x-raw-rgb,width=320,height=240 ! ffmpegcolorspace ! queue ! glimagesink sync=false
>>
>> I get:
>> Estableciendo el conducto a PAUSA ?
>> El conducto est? PREPAR?NDOSE ?
>>
>> But the pipeline never goes to PLAYING and nothing happen (i can't see the result)...
>>
>> Any idea??
>>
>> Thanks in advance
>
> Regards,
> George
>
> [1]. http://gstreamer.freedesktop.org/data/doc/gstreamer/head/qt-gstreamer/html/bus_8cpp_source.html
> _______________________________________________
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Matías Hernandez Arellano
Ingeniero de Software/Proyectos en VisionLabs S.A
CDA Archlinux-CL
www.msdark.archlinux.cl
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