how can I process certien frames from a video?

I uploaded a 5 minutes video and I want to process only the first 2 minutes, then the seconed 2 minute and so on...

should I use a windo or frame size or how can I do that?

[Walter Roberson]

Are you streaming the video from a source, such as youtube? Possibly one using H.264 ? Or do you have a local copy of the video file that you can read from? Or is it at least stored on a network drive (even if that does mean OneDrive) where it can be accessed as a file ?

[Duaa Habib]

yes i have a local copy of the video

Answer 1

[Cris LaPierre]

How are you reading in your frames? Are you using VideoReader?

I haven't tried it, but following the examples on the linked page, I would look into using the CurrentTime property as my while loop conditional instead of hasFrame.

Maybe something like this?

v = VideoReader('xylophone.mp4');

while v.CurrentTime < 120
    frame = readFrame(v);
end

[Duaa Habib]

what does 120 represents here

[Cris LaPierre]

Current time. I linked to the description in my original post.

[Duaa Habib]

I see, thanks.

do you know how can I write code to take one frame every nth of frames until the number of frames ends, for example if the video has 60 frames per second and I want to make it 30 frames per second

[Cris LaPierre]

Perhaps this answer? https://www.mathworks.com/matlabcentral/answers/826115-change-frame-rate-of-video-file?s_tid=ans_recom_leaf

Otherwise, you could use code similar to the above, and have two calls to readFrame in each loop, and just ignore the data from one of them.

You could also figure out the number of frames in your video (Duration and FrameRate properties) and then use a loop to load the specific frames you want using read with the frame specified.

[Walter Roberson]

v = VideoReader('xylophone.mp4');
every_n = 2;
seconds_to_process = 120;

fc = 0;
while hasFrame(v) && v.CurrentTime < seconds_to_process
    frame = readFrame(v);
    fc = fc + 1;
    if mod(fc, every_n) == 0
        do something with frame
    end
end

It is possible to ask to read specific frames. For example you could ask to

read(v, 2:2:119)

and get those frames in a block. However it is generally faster not to ask for specific frames by number, at least not if you are asking one-by-one.