Using 5dpo
lazarus / 39-Graphics

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l_netwalker · 2011-02-04 19:55

Hi all,

I try to use the 5dbo V4l Component to read images from my USB Cam.
I did a v4l-info and found out that the cam produces JPG images.
Code: [Select]video capture
    VIDIOC_ENUM_FMT(0,VIDEO_CAPTURE)
        index                   : 0
        type                    : VIDEO_CAPTURE
        flags                   : 1
        description             : "JPEG"
        pixelformat             : 0x4745504a [JPEG]
    VIDIOC_G_FMT(VIDEO_CAPTURE)
        type                    : VIDEO_CAPTURE
        fmt.pix.width           : 176
        fmt.pix.height          : 144
        fmt.pix.pixelformat     : 0x4745504a [JPEG]
        fmt.pix.field           : NONE
        fmt.pix.bytesperline    : 176
        fmt.pix.sizeimage       : 10094
        fmt.pix.colorspace      : JPEG
        fmt.pix.priv            : 1

so I thought  the following way I should get an image
( it's the modified example )
Code: [Select]
procedure TFMain.VideoFrame(Sender: TObject; FramePtr: PByte);
begin
  FrameRate:=round(1/((GetTickCount-FrameTime)/1000)*0.5 +
FrameRate*0.5);
  FrameTime:=GetTickCount;
  Caption:= 'SdpoVideo4L2 '+IntToStr(FrameRate)+'fps';
  TEMPGraphic := TJpegImage.Create;
  //TEMPGraphic.LoadFromFile('/home/hartmut/Documents/Pictures/hucky-
100x137.jpg');
  TEMPGraphic.Height := Video.Height;
  TEMPGraphic.Width := Video.Width;
  JPGPointer := pointer(TEMPGraphic);

  Move(FramePtr,JPGPointer , SizeOf(TEMPGraphic));

  TEMPBitmap := TBitmap.Create;
  TEMPBitmap.Height := Video.Height;
  TEMPBitmap.Width := Video.Width;
  TEMPBitmap.Canvas.Draw(0,0,TEMPGraphic);
  Image1.Picture.Graphic := TEMPBitmap;
  TEMPGraphic.Free;
end;


As far as I understood the example, the procedure  TFMain.VideoFrame
is called with every new frame from the camera, with FramePtr as a
pointer
to this actual JPEG encode frame. To get it to the screen I first
generate a JPEG image, which I the copy with the move command to a
TImage.

But all I get is grahical garbage. It's my first work with Lazarus and
I have no ideas how to get this up and working.

Any suggestions or hints on a solution ?

Thanks
Hartmut

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Marc · 2011-02-05 15:41

why do you think moving framebuffer data over the TJpegImage class
suddenly decodes a jpeg image ?
Pit the framedata in a memorystream and let the TEMPGraphic read it.

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circular · 2011-02-06 01:28

That's right, you are erasing the objet structure with bitmap data.
Bitmap data is a stream whereas an object is a dynamic structures
containing pointers to active memory.

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prof7bit · 2011-05-06 09:06

In the latest svn version of 5dpo (svn release >= 101) there is now a
property UseLibV4l, if you set it to True it will access the device
though the libv4l wrapper (part of the v4l-utils, should be installed
already, its part of the official v4l2 infrastructure).

This will do format conversion transparently on the fly. All cams will
gain the ability to support:

RGB24
BGR24
YUV240

even if they do not support this format natively (very likely since
all format conversion, decompression, etc. has been removed from the
kernel drivers and moved into libv4l).

Bernd