C# extract frames from part of a video file

Question

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?

Answer 1

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.)