How to get pointer to a gstBuffer with QtGSTreamer

[pfarmer]

Hello,
How can I get a pointer to a gstBuffer with QtGSTreamer?

I want to combine a 3D rendering library with GStreamer. In order to display some 2D video content in the rendering frame i need the following image data format:
RGBRGBRGB... each letter is one byte; which corresponds to the following GStreamer caps:

const char *caps = "video/x-raw-rgb, bpp=(int)24, depth=(int)24, endianness=(int)4321, red_mask=(int)16711680, green_mask=(int)65280, blue_mask=(int)255"

Thus I would like to have something like the following pipeline:

SoImage* image();
MySink m_sink(image);
const char* location = "C:/Users/Public/Videos/Sample Videos/Wildlife.wmv";	
QString pipe1Descr = QString("filesrc location=\"%1\" ! decodebin2 ! ffmpegcolorspace ! "
                                 "appsink name=\"mysink\" caps=\"%2\"").arg(location, caps);
    pipeline1 = QGst::Parse::launch(pipe1Descr).dynamicCast<QGst::Pipeline>();
    m_sink.setElement(pipeline1->getElementByName("mysink"));

The Apllicationsink may look like this:

const int resX = 640;
const int resY = 480;
const int bytesPerPixel = 3;


class MySink : public QGst::Utils::ApplicationSink
{
public:
    MySink(SoImage* image)
        : QGst::Utils::ApplicationSink(), m_image(image) {}

protected:
    virtual QGst::FlowReturn newBuffer()
    {
       // Pointer to the above mentioned image data
       unsigned char* imageDataPtr;
        // Here should be some casting from the BufferPtr to a native C pointer 
        // And may be some locking mechanism for the buffer in order to be able to copy the whole data
        // QGst::BufferPtr  bufferPtr =  pullBuffer();
       // The image.setValue function can copy the data to its own memory
       m_image->image.setValue(SbVec2s(resX,resY), bytesPerPixel, imageDataPtr );
        return QGst::FlowOk;
    }
private:
    SoImage* m_image;
};

This is adopted from the appsink-src example. But in there the BufferPtr retunred from pullBuffer() is simple passed to pushbuffer().
m_src->pushBuffer(pullBuffer()). Thus no casting nesessary there.

Does the wrap function of the BufferPtr would help in this case? If, then how could I use it?
Any help/suggestions on how to achive the functions described in the comments of MySink::newBuffer() would be very appriciated.

The 3D rendering library is Coin3D.

[George Kiagiadakis]

On Tue, Apr 17, 2012 at 12:22 PM, pfarmer <[hidden email]> wrote:
> Hello,
> How can I get a pointer to a gstBuffer with QtGSTreamer?
>
> I want to combine a 3D rendering library with GStreamer. In order to display
> some 2D video content in the rendering frame i need the following image data
> format:
> RGBRGBRGB... each letter is one byte; which corresponds to the following
> GStreamer caps:
>

Why would you want to get a GstBuffer pointer when what you really
want is to get the data of the buffer? bufferptr->data() should do
that in QtGStreamer. But if you really really want a GstBuffer*, then
you can just get it implicitly from a smart pointer:

QGst::BufferPtr bufferptr;
GstBuffer *b = bufferptr;
gst_buffer_ref(b);
....

Regards,
George
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[pfarmer]

Thanks

I actualy would like to have the data from the buffer. So that would be ideal:
bufferptr->data().  

And it works. This was what I was searching for. Simple enough.

So the newBuffer() function looks like this:

    virtual QGst::FlowReturn newBuffer()
    {
		bufferPtr = pullBuffer();
		unsigned char* imageData = static_cast<unsigned char*>(bufferPtr->data());
		m_image->image.setValue(SbVec2s(resX,resY), bytesPerPixel, imageData );        
        return QGst::FlowOk;
    }

Is this good to use?

Is it garanteed that the data in the Buffer stayes untouched during the copy process in the image.setValue() function? Or do I have to take special care?

data() function returns a pointer to quint8. So I have to assume that quint8 is the same as uchar on the machine. Is there a better way for the conversion?

[George Kiagiadakis]

On Tue, Apr 17, 2012 at 1:51 PM, pfarmer <[hidden email]> wrote:

> Thanks
>
> I actualy would like to have the data from the buffer. So that would be
> ideal:
> bufferptr->data().
>
> And it works. This was what I was searching for. Simple enough.
>
> So the newBuffer() function looks like this:
>
>
>
> Is this good to use?

Sorry, I don't see any code here...

> Is it garanteed that the data in the Buffer stayes untouched during the copy
> process in the image.setValue() function? Or do I have to take special care?
>
> data() function returns a pointer to quint8. So I have to assume that quint8
> is the same as uchar on the machine. Is there a better way for the
> conversion?

Yes, quint8 is a typedef for unsigned char.
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[pfarmer]

Sorry. Strange. Here again:


Thanks

I actualy would like to have the data from the buffer. So that would be ideal:
bufferptr->data().  

And it works. This was what I was searching for. Simple enough.

So the newBuffer() function looks like this:

    virtual QGst::FlowReturn newBuffer()
    {
                bufferPtr = pullBuffer();
                unsigned char* imageData = static_cast<unsigned char*>(bufferPtr->data());
                m_image->image.setValue(SbVec2s(resX,resY), bytesPerPixel, imageData );        
        return QGst::FlowOk;
    }



Is this good to use?

Is it garanteed that the data in the Buffer stayes untouched during the copy process in the image.setValue() function? Or do I have to take special care?

data() function returns a pointer to quint8. So I have to assume that quint8 is the same as uchar on the machine. Is there a better way for the conversion?

[George Kiagiadakis]

On Wed, Apr 18, 2012 at 11:42 AM, pfarmer <[hidden email]> wrote:

> So the newBuffer() function looks like this:
>
>    virtual QGst::FlowReturn newBuffer()
>    {
>                bufferPtr = pullBuffer();
>                unsigned char* imageData = static_cast<unsigned char*>(bufferPtr->data());
>                m_image->image.setValue(SbVec2s(resX,resY), bytesPerPixel, imageData );
>        return QGst::FlowOk;
>    }
>
>
>
> Is this good to use?

It should work, yes.

> Is it garanteed that the data in the Buffer stayes untouched during the copy
> process in the image.setValue() function? Or do I have to take special care?

Yes, as long as there is a BufferPtr holding this buffer in the active
scope, the data will stay there, unmodified.
I would recommend you to create the BufferPtr in the scope of this
function, though, so that it gets destroyed when the function returns.
There is no reason to keep a reference to the buffer longer than you
need it.
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[pfarmer]

Thanks again.

Okay, I create the QGst::bufferPtr now inside the virtual QGst::FlowReturn newBuffer() function