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QWidget Flickering for frame by frame streaming of video

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qwidgetqpainteventflickeringvideopixmap
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  • mrjjM mrjj

    Hi
    How much higher res from when its working ?

    S Offline
    S Offline
    SilverSurfer
    wrote on last edited by
    #4

    @mrjj
    Hi,
    Max Non-flickering resolution = 3200 * 1800
    My requirement is 4k(3840 * 2160)

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    • J.HilkJ J.Hilk

      @SilverSurfer
      hi, my guess would be, loadFromData takes longer than 34 ms, by higher resolutions. or the Drawing itself or the combination of both.

      I would suggest drawing more bitmaps beforehand in some kind of buffer, preferably threaded so you can do more than one drawing at once.

      THan access those premade bitmaps in your main thread, taking the oldest one from the buffer,for example a QList<QPixmaps>, and painting that one in your paintEvent.

      S Offline
      S Offline
      SilverSurfer
      wrote on last edited by SilverSurfer
      #5

      @J.Hilk
      Yes, loadFromData does take longer than 34ms(in fact 50ms at 4k resolution).

      This is for live streaming from IP Cameras, so I don't have the bitmaps beforehand.
      I do fetch bitmaps in a background thread and emit an signal (getImageData() is slot to this signal) to the main thread when they are available.

      The Flicker goes away if I reduce the fps, whereas loadFromData time remains the same. So is it really responsible for the flicker?

      I am also observing a lag which I think is because of loadFromData time.

      Is there any other way to draw an Image considering I have bitmap data in an unsigned char array ?

      J.HilkJ 1 Reply Last reply
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      • S SilverSurfer

        @J.Hilk
        Yes, loadFromData does take longer than 34ms(in fact 50ms at 4k resolution).

        This is for live streaming from IP Cameras, so I don't have the bitmaps beforehand.
        I do fetch bitmaps in a background thread and emit an signal (getImageData() is slot to this signal) to the main thread when they are available.

        The Flicker goes away if I reduce the fps, whereas loadFromData time remains the same. So is it really responsible for the flicker?

        I am also observing a lag which I think is because of loadFromData time.

        Is there any other way to draw an Image considering I have bitmap data in an unsigned char array ?

        J.HilkJ Offline
        J.HilkJ Offline
        J.Hilk
        Moderators
        wrote on last edited by
        #6

        @SilverSurfer
        I can think of 2 ways to do it.

        • don't stream directly, but delay the showing by a second or two, save your calculated images to a buffer and take from that to show in your application. Every so often you'll need to skip frames however

        • Split your image into 2, e.g. upper half and lower one, do the Pixmap modifications in 2 different threads and union that to images into one. This could bring you below the needed threshold.


        Be aware of the Qt Code of Conduct, when posting : https://forum.qt.io/topic/113070/qt-code-of-conduct


        Q: What's that?
        A: It's blue light.
        Q: What does it do?
        A: It turns blue.

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        • S Offline
          S Offline
          SilverSurfer
          wrote on last edited by
          #7

          Is there any way I can avoid loadFromData() call, which I assume is doing a copy somewhere ?

          To rephrase my question:
          Can't I draw an Image from the existing buffer without a need for the copy? If yes , How?

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          • SGaistS Offline
            SGaistS Offline
            SGaist
            Lifetime Qt Champion
            wrote on last edited by
            #8

            Hi,

            How are you getting the data in the first place ?

            Interested in AI ? www.idiap.ch
            Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

            S 1 Reply Last reply
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            • SGaistS SGaist

              Hi,

              How are you getting the data in the first place ?

              S Offline
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              SilverSurfer
              wrote on last edited by
              #9

              @SGaist
              By making a call to a server to fill the passed buffer.

              //time take by this depends size of buffer to be fetched
              //which may be more than 34 ms depending on size
              fetchBitmap(handle, cameraId,(uchar*)buffer , x_width, y_height);
              
              emit bufferAvailable(buffer,size); //calls getImageData(..) slot in the UI thread
              

              Thanks!

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              • SGaistS Offline
                SGaistS Offline
                SGaist
                Lifetime Qt Champion
                wrote on last edited by
                #10

                What is that server ?

                What does it provide as API to retrieve images ?

                Interested in AI ? www.idiap.ch
                Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

                S 1 Reply Last reply
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                • SGaistS SGaist

                  What is that server ?

                  What does it provide as API to retrieve images ?

                  S Offline
                  S Offline
                  SilverSurfer
                  wrote on last edited by
                  #11

                  @SGaist
                  It is a Video Management Server(ExacqVision Server to be precise).

                  Yes, the API( fetchBitmap(...)) is provided by the server.
                  So I don't think the data retrieval time can be reduced.

                  What I would Ideally like to do is avoid any copying for this data.
                  Which happens when I do pixmap->loadFromData(...) .

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                  • SGaistS Offline
                    SGaistS Offline
                    SGaist
                    Lifetime Qt Champion
                    wrote on last edited by
                    #12

                    Is their API documentation accessible somewhere ?

                    If you pass the buffer to the fetchBimap method, then you should be able to pass a QImage buffer pointer and in this case, the data will be copied directly on the QImage that you can then manipulate.

                    Interested in AI ? www.idiap.ch
                    Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

                    S 1 Reply Last reply
                    1
                    • SGaistS SGaist

                      Is their API documentation accessible somewhere ?

                      If you pass the buffer to the fetchBimap method, then you should be able to pass a QImage buffer pointer and in this case, the data will be copied directly on the QImage that you can then manipulate.

                      S Offline
                      S Offline
                      SilverSurfer
                      wrote on last edited by SilverSurfer
                      #13

                      @SGaist
                      No the Documentation is not available publicly.

                      It take a uint8_t* as buffer argument.

                      //registered with server
                      Callback(event)
                      {
                          if(event == LIVE_FRAME_AVAILABLE)
                      {
                          frameSize = fetchBitmap(NULL); 
                          // Size fetched everytime as this can change with every frame if image is resized
                          vector.resize(framesize)
                          fetchBitmap(&vector[0]);
                          emit bufferAvailable(&vector[0],frameSize);
                      }
                      }
                      

                      I am not sure how can I use QImage pointer here.

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                      • SGaistS Offline
                        SGaistS Offline
                        SGaist
                        Lifetime Qt Champion
                        wrote on last edited by
                        #14

                        QImage::bits.

                        Make the QImage the correct format and size.

                        Interested in AI ? www.idiap.ch
                        Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

                        S 1 Reply Last reply
                        1
                        • SGaistS SGaist

                          QImage::bits.

                          Make the QImage the correct format and size.

                          S Offline
                          S Offline
                          SilverSurfer
                          wrote on last edited by
                          #15

                          @SGaist
                          Tried using
                          QImage::QImage(uchar * data, int width, int height, Format format, QImageCleanupFunction cleanupFunction = 0, void * cleanupInfo = 0)

                          data = pixel data , updated by fetchBitmap(..) function above.
                          format = RGB888
                          where as per documentation it does not do a deep copy. So this helps.

                          But my image has R and B planes swapped.
                          Can't seem to find the appropriate format .

                          P.S: I am on a Windows machine.

                          Thanks,
                          Kshitij Mayekar

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                          0
                          • SGaistS Offline
                            SGaistS Offline
                            SGaist
                            Lifetime Qt Champion
                            wrote on last edited by
                            #16

                            See QImage::rgbSwapped

                            Interested in AI ? www.idiap.ch
                            Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

                            S 1 Reply Last reply
                            1
                            • SGaistS SGaist

                              See QImage::rgbSwapped

                              S Offline
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                              SilverSurfer
                              wrote on last edited by
                              #17

                              @SGaist
                              QImage::rgbSwapped results in creating new QImage with is equivalent to deep copy. So It does not help. Is there any other way to dislaying the RGB planes correctly ?

                              Note: Whenever I write the contents of the buffer to a file with appropriate headers I could see the Image correctly when I open the Image through windows photo viewer.

                              Original Problem Statement : Display Byte Buffer(uchar*) to a QWidget without the need to deep Copy .

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                              • SGaistS Offline
                                SGaistS Offline
                                SGaist
                                Lifetime Qt Champion
                                wrote on last edited by
                                #18

                                Where are these frames coming from ?

                                Interested in AI ? www.idiap.ch
                                Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

                                S 1 Reply Last reply
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                                • SGaistS SGaist

                                  Where are these frames coming from ?

                                  S Offline
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                                  SilverSurfer
                                  wrote on last edited by
                                  #19

                                  @SGaist

                                  These frames are received from a server.

                                  //Api that talks to server
                                  fetchBitmap(&vector[0]);
                                  

                                  I do not have access to server code.

                                  P.S: Server Machine is Linux and Client is Windows . Could this be the reason for RGB /BGR mismatch ?

                                  mrjjM 1 Reply Last reply
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                                  • W Offline
                                    W Offline
                                    wrosecrans
                                    wrote on last edited by
                                    #20

                                    Is there any chance of the paint event being triggered by the system at a moment when the pixmap isn't fully populated? If that is possible, you would get flickering regardless of whether the load function is faster or slower than real time.

                                    1 Reply Last reply
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                                    • S SilverSurfer

                                      @SGaist

                                      These frames are received from a server.

                                      //Api that talks to server
                                      fetchBitmap(&vector[0]);
                                      

                                      I do not have access to server code.

                                      P.S: Server Machine is Linux and Client is Windows . Could this be the reason for RGB /BGR mismatch ?

                                      mrjjM Offline
                                      mrjjM Offline
                                      mrjj
                                      Lifetime Qt Champion
                                      wrote on last edited by
                                      #21

                                      @SilverSurfer said in QWidget Flickering for frame by frame streaming of video:

                                      Could this be the reason for RGB /BGR mismatch ?

                                      Well there is always Endianness but if using same sort of CPU in both ends, its likely not related to that.

                                      S 1 Reply Last reply
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                                      • mrjjM mrjj

                                        @SilverSurfer said in QWidget Flickering for frame by frame streaming of video:

                                        Could this be the reason for RGB /BGR mismatch ?

                                        Well there is always Endianness but if using same sort of CPU in both ends, its likely not related to that.

                                        S Offline
                                        S Offline
                                        SilverSurfer
                                        wrote on last edited by
                                        #22

                                        @mrjj
                                        Both machines are little endian.

                                        mrjjM 1 Reply Last reply
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                                        • S SilverSurfer

                                          @mrjj
                                          Both machines are little endian.

                                          mrjjM Offline
                                          mrjjM Offline
                                          mrjj
                                          Lifetime Qt Champion
                                          wrote on last edited by
                                          #23

                                          @SilverSurfer
                                          Ok. so most likely they
                                          are just using openCV and send as BGR888

                                          So i dont see any way to convert to supported format without copy.

                                          W 1 Reply Last reply
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