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A video player can interpret a file(mp4,avi...)to picture on screen. Qt can draw lines,rectangles,pixmap...to picture on screen. What is the difference between them?

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It depends on what Qt paint engine and what video player. The raster paint engine and the OpenGL paint engine are completely different for instance. If your video player is hardware accelerated, it might write to a completely different layer and there would be no relation whatsoever with graphics. –  Luca Carlon Jan 29 '12 at 13:56
A video player is just an application. Qt is a library to write applications. So you can implement a video player in Qt. On which criteria do you want to compare both of them? –  UmNyobe Jan 30 '12 at 10:05
For example,Qt draw 24 pictures on a QLabel per second,this is what I can imagine;The rapidly changing picture on the video player is same as former? –  gemfield Jan 31 '12 at 1:53
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You're comparing apples to oranges. They are completely different.

  • A video player reads a video stream from a file and decodes it using a decoder (DivX, XviD, x.264, etc.), displaying the output on your screen.

  • Qt4's object painting allows you to paint pixels onto a QObject. That's basically it.

Video decoders are heavily optimized and some even use GPU acceleration. Qt4's object painting isn't made for rapidly-changing frames and is used do draw basic things.

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In my opinion,video player call operating system API to implement its function,and Qt too.So what's difference between the operating system API? –  gemfield Jan 29 '12 at 12:43
Well, you're comparing them on a completely different basis. What is this OS API you speak of? –  Blender Jan 29 '12 at 14:09
I used to programming with Qt,compares with video player,I have a illusion that video player can paint more data on the screen.As you said"reads a video stream from a file and decodes it using a decoder,displaying the output on your screen",(for example,on a X11 system),the process of decode and display(of video player) have used X11 API? –  gemfield Jan 31 '12 at 2:02
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