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Using AForge ffmpeg wrapper you can extract frames from a video using the VideoFileReader class and save it as a bitmap.

See this for the exemple: Extracting frames of a .avi file

My problem with that is that you cannot specified where to start reading the frames. It always starts from the beginning of the video file.

But what if i wanted to extract frames that are in the middle of a two hours long video file. Using that class you'd have to parse the whole first hour juste to get to those frames.

Does anyone know a way to achieve that?

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SiriusNik
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  • Seems they did not provide a way for doing that. You could try to cheat by cutting the file using a different library, or just use a different library to extract frames to begin with. EDIT: You can totally debug and see the private members of the `VideoFileReader` instance, and see if maybe Reflection can help you here. – SimpleVar Feb 12 '15 at 23:54
  • Looks like a good answer to me, did it not suit you? – Kyle Gobel Feb 06 '16 at 00:25
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    If you are developing for UWP then watch this: https://stackoverflow.com/a/49395297/2733404 – Oleksandr Bilyk Mar 20 '18 at 22:43

1 Answers1

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If you know where in the video you want to start reading, just skip the appropriate number of frames; there's no need to process any of them.

This assumes, of course, that you know the exact frame number you want to start reading from, which you can calculate by multiplying the framerate by the time at which you want to perform the extraction. In your example, if the video is two hours long and you want to extract frames from the middle...

VideoFileReader reader = new VideoFileReader();
reader.Open("file.avi");

// Jump to 1 hour into the video
int framesToSkip = reader.FrameRate * 3600;    // 1 hour = 3600 seconds
for (int i = 0; i < framesToSkip; i++)
    reader.ReadVideoFrame();

// Now the next time ReadVideoFrame() is called, we will get the frame at the 1 hour mark

This assumes that the .FrameRate property returns the value in frames per second. Unfortunately the documentation doesn't say, so I'm not sure how it handles video files with non-integral framerates (i.e. 29.97 is a common framerate.)

Reticulated Spline
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    This unfortuantely seems to currently be the only way with the AForge/Accord wrapper. I would add if you use this method to dispose each frame that you're throwing away, ``videoFrame.Dispose()`` (within the skipping loop) otherwise you'll get errors after around 1k frames. – Kyle Gobel Feb 06 '16 at 00:54