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What's a good efficient way to reverse a QMovie to play it backwards?

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  • JonBJ JonB

    @GrecKo
    Purely ooi for me. What kind of QTimer do you use? From my limited understanding of this stuff you need the human to see at least 50 frames per second, right? Is QTimer "accurate" and "consistent" enough to make this smooth, or does it get "lumpy" as the timeouts vary in accuracy?

    jsulmJ Offline
    jsulmJ Offline
    jsulm
    Lifetime Qt Champion
    wrote on last edited by
    #13

    @JonB said in What's a good efficient way to reverse a QMovie to play it backwards?:

    human to see at least 50 frames per second

    Smartass mode: 24 actually :-)

    https://forum.qt.io/topic/113070/qt-code-of-conduct

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    • JonBJ Online
      JonBJ Online
      JonB
      wrote on last edited by
      #14

      OK, so does a default precision QTimer tick accurately at at least 24 per second? Not to mention that presumably if the OS is off doing something it won't, but perhaps all movie players would suffer from that issue?

      jsulmJ 1 Reply Last reply
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      • JonBJ JonB

        OK, so does a default precision QTimer tick accurately at at least 24 per second? Not to mention that presumably if the OS is off doing something it won't, but perhaps all movie players would suffer from that issue?

        jsulmJ Offline
        jsulmJ Offline
        jsulm
        Lifetime Qt Champion
        wrote on last edited by
        #15

        @JonB Such low frequencies should be fine for QTimer I would say.
        https://doc.qt.io/qt-6/qt.html#TimerType-enum
        "On UNIX (including Linux, macOS, and iOS), Qt will keep millisecond accuracy for Qt::PreciseTimer.
        ...
        On Windows, Qt will use Windows's Multimedia timer facility (if available) for Qt::PreciseTimer
        "

        https://forum.qt.io/topic/113070/qt-code-of-conduct

        JonBJ 1 Reply Last reply
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        • jsulmJ jsulm

          @JonB Such low frequencies should be fine for QTimer I would say.
          https://doc.qt.io/qt-6/qt.html#TimerType-enum
          "On UNIX (including Linux, macOS, and iOS), Qt will keep millisecond accuracy for Qt::PreciseTimer.
          ...
          On Windows, Qt will use Windows's Multimedia timer facility (if available) for Qt::PreciseTimer
          "

          JonBJ Online
          JonBJ Online
          JonB
          wrote on last edited by
          #16

          @jsulm Indeed, that is for Qt::PreciseTimer option, which is why I was asking about the "default" mode, which is something like "coarse".

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          • GrecKoG Offline
            GrecKoG Offline
            GrecKo
            Qt Champions 2018
            wrote on last edited by
            #17

            QMovie uses a default QTimer.

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            • M Mizmas

              @jeremy_k Do you mean for the laggy animation? I've tried it, but I didn't get a noticeable performance improvement. I'm using a .webp animation file though to have a full transparency channel, if I use .gif the lag is minimal, but it doesn't have full transparency, only 0 or 1

              jeremy_kJ Offline
              jeremy_kJ Offline
              jeremy_k
              wrote on last edited by
              #18

              @Mizmas said in What's a good efficient way to reverse a QMovie to play it backwards?:

              @jeremy_k Do you mean for the laggy animation? I've tried it, but I didn't get a noticeable performance improvement.

              Yes, to decrease the time required to access each frame when playing in reverse. Have you profiled the code to verify that the animation is a hotspot?

              I'm using a .webp animation file though to have a full transparency channel, if I use .gif the lag is minimal, but it doesn't have full transparency, only 0 or 1

              Webp uses VP8, which stores key frames and intermediate frames that modify earlier frames. Jumping to a frame may require reconstructing prior frames first.

              Asking a question about code? http://eel.is/iso-c++/testcase/

              M 1 Reply Last reply
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              • jeremy_kJ jeremy_k

                @Mizmas said in What's a good efficient way to reverse a QMovie to play it backwards?:

                @jeremy_k Do you mean for the laggy animation? I've tried it, but I didn't get a noticeable performance improvement.

                Yes, to decrease the time required to access each frame when playing in reverse. Have you profiled the code to verify that the animation is a hotspot?

                I'm using a .webp animation file though to have a full transparency channel, if I use .gif the lag is minimal, but it doesn't have full transparency, only 0 or 1

                Webp uses VP8, which stores key frames and intermediate frames that modify earlier frames. Jumping to a frame may require reconstructing prior frames first.

                M Offline
                M Offline
                Mizmas
                wrote on last edited by Mizmas
                #19

                @jeremy_k Thanks for the help. What I did was create a minimal new .py file with only a QLabel and a QMovie to only test the animation, and the performance is exactly the same as in the video I shared before, so it seems that there was nothing bottlenecking the animation in my main app code. I'm on PyQt6 6.7.1 if that helps.
                On the left it's opened on Chrome, and on the right PyQt6 window:

                from PyQt6.QtWidgets import QApplication, QLabel
                from PyQt6.QtGui import QMovie
                import sys
                import resources
                
                app = QApplication(sys.argv)
                label = QLabel()
                label.setStyleSheet("background: black;")
                movie = QMovie(':/Animations/b_mode.webp')
                movie.setCacheMode(QMovie.CacheMode.CacheAll)
                print(movie.cacheMode())
                print(movie.format())
                label.setMovie(movie)
                label.setFixedSize(50, 50)
                label.show()
                movie.start()
                sys.exit(app.exec())
                
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                • jeremy_kJ Offline
                  jeremy_kJ Offline
                  jeremy_k
                  wrote on last edited by
                  #20

                  @Mizmas Thanks for providing the POC. I gave it a quick try with a test image, but apparently my Qt installation lacks webp movie support.

                  The image on the right appears to be less smooth than the one on the left. Does it look any better if the label is allowed to assume its implicit size from the QMovie rather than being set to 50x50?

                  Asking a question about code? http://eel.is/iso-c++/testcase/

                  M 1 Reply Last reply
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                  • jeremy_kJ jeremy_k

                    @Mizmas Thanks for providing the POC. I gave it a quick try with a test image, but apparently my Qt installation lacks webp movie support.

                    The image on the right appears to be less smooth than the one on the left. Does it look any better if the label is allowed to assume its implicit size from the QMovie rather than being set to 50x50?

                    M Offline
                    M Offline
                    Mizmas
                    wrote on last edited by
                    #21

                    @jeremy_k Here's an answer I got on stackoverflow: https://stackoverflow.com/questions/79672044/qmovie-is-stuttering-lagging-when-using-an-animated-webp-file-on-both-pyqt6-a/79672867#79672867

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                    • SGaistS Offline
                      SGaistS Offline
                      SGaist
                      Lifetime Qt Champion
                      wrote on last edited by
                      #22

                      From the looks of it, it seems like having the animation available for both direction is the easy path.

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

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