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  • University of Sussex

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  1. How to display opencv video in pyqt ... How to display opencv video in pyqt apps
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    The code for this tutorial is [here](https://github.com/docPhil99/opencvQtdemo)
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    Opencv provides are useful, but limited, method of building a GUI. A much more complete system could be acheived using pyqt.
    
              
    
              
    
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    The question is, how do we display images. There are quite a few possible routes but perhaps the easiest is to use `QLabel` since it has a `setPixmap` function. Below is some code that creates two labels. It then creates a grey pixmap and displays it one of the labels. [code: staticLabel1.py](https://github.com/docPhil99/opencvQtdemo/blob/master/staticLabel1.py)
    
              
    
              
    
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        Mac webcam FFmpeg  Mac webcam FFmpeg      
    

          
    
              
    
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    #Capture and stream a webcam
    
              
    
              
    
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    To capture using the iSight camera on a Mac, or infact any other webcam connected to the Mac, we can use FFmpeg. First get a list of the devices installed.
    
              
    
              
    
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    ```
    
              
    
              
    
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    ffmpeg -f avfoundation -list_devices true -i "" 
    
              
    
          
    
    
    
  
    

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          opencvQtdemo  opencvQtdemo          Public
        
    
      
    


      
    
        Using opencv and QT together
      
    

      
    
          
  
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        How to write lossless video in Python  How to write lossless video in Python      
    

          
    
              
    
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    OpenCV does a reasonable job of reading videos from file or webcams. It's simple and mostly works. When it comes to writing videos, 
    
              
    
              
    
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    it however leaves a lot to be desired. There is little control over the codecs and it is almost impossible to know which codecs are installed. It also wants to know things like the frame size at intailisation. This isn't always a problem, but if you don't know it yet it means you have to set up the video writer inside your main processing loop. 
    
              
    
              
    
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    To make something as cross-platform compatible as possible it would be nice to use FFmpeg. There are a few python wrappers around, but as far as I can tell they are mainly used for transcoding type applications. One solution is run FFmpeg as a subprocess and set its input to accept a pipe. Then every video frame is passed through the pipe. You write this yourself, in fact it's only a few lines of code. However, the [scikit-video](http://www.scikit-video.org/stable/index.html) package will do this for us, with some nice boilerplate to make life easier.
    
              
    
              
    
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