Repository: opencv
Issue: OpenCV - How to create video with a transparent background?
Labels: question (invalid tracker)

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##### System information (version)
<!-- Example
- OpenCV => 4.2
- Operating System / Platform => Windows 64 Bit
- Compiler => Visual Studio 2017
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- OpenCV => 4.5
- Operating System / Platform => Windows 64 Bit
- Compiler => vscode

##### Detailed description
The file types that currently support an Alpha (transparency) channel are mov, AVI, Quicktime, and WebM. If I have some transparent png images, how can I use opencv to generate transparent background video?


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##### Steps to reproduce

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    ```.cpp
    // C++ code example
    ```
 or attach as .txt or .zip file
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If you use ffmpeg, the command is as follows
```
ffmpeg -i input%04d.png out.mov
```

##### Issue submission checklist

 - [ √] I report the issue, it's not a question
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 - [√ ] I checked the problem with documentation, FAQ, open issues,
       forum.opencv.org, Stack Overflow, etc and have not found any solution
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 - [ √] I updated to the latest OpenCV version and the issue is still there
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   master branch for OpenCV 4.x and 3.4 branch for OpenCV 3.x releases.
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 - [√ ] There is reproducer code and related data files: videos, images, onnx, etc
   <!--
   The best reproducer -- test case for OpenCV that we can add to the library.
   Recommendations for media files and binary files:
   * Try to reproduce the issue with images and videos in opencv_extra repository
     to reduce attachment size
   * Use PNG for images, if you report some CV related bug, but not image reader
     issue
   * Attach the image as an archive to the ticket, if you report some reader issue.
     Image hosting services compress images and it breaks the repro code.
   * Provide ONNX file for some public model or ONNX file with random weights,
     if you report ONNX parsing or handling issue. Architecture details diagram
     from netron tool can be very useful too. See https://lutzroeder.github.io/netron/
   -->