Skipping frames and retrieving movie file in Matlab

Question

I am trying to process a video in Matlab that I read in using VideoReader. I can process the the frames without a problem, but I only want to process every fift

Answer 1

Don`t know if this is still of use but I´ve found a way to work around the issue.

As the readFrame reads the CURRENT frame, provided by the vid.CurrentTime property you can simply advance the property by the amount of frames you want to skip.

vid = VideoReader('myvid.mpeg')
vidFig = figure();
currAxes = axes;

n = 10;

while hasFrame(vid) 
vidFrame = readFrame(vid);
vid.CurrentTime = vid.CurrentTime + n/vid.FrameRate; 
image(vidFrame, 'Parent', currAxes);
currAxes.Visible = 'off';
end

Changing the value of n makes the video skip the amount of frames through every loop. I hope this helped.

Answer 2

I've had this issue too. Without using deprecated code, the only way to do what you are trying is to call readFrame five times for every output frame. This is slow and very inefficient. However, if you use the deprecated read method (and assuming your video is a file rather than a stream), you can specify a frame number as well. I don't know why The MathWorks have gone backwards on this. I suggest that you file a service request to ask about it and say why this functionality is important to you.

In the meantime, you can try out my frame2jpg function that extracts particular frames from a video file. It tries to use the deprecated read method and falls back to readFrame if that fails. I've found the read method to be ten times faster in my own application with 1080p 60 fps MPEG-4 video. Feel free to modify the code to suit your your needs.