How read frames within specified time interval exactly from video?

Hi, everyone.

In Matlab R2017b, I tried to read video frames within specified time interval in this URL ->(https://jp.mathworks.com/help/matlab/import_export/read-video-files.html?searchHighlight=CurrentTime&s_tid=doc_srchtitle)

However, I could not read frames in exact time. When I tried this, extracted frames is always misaligned about 15 frames from the original video.

Are there any ideas for solving this problem or another way to read frames?

[Tohru Kikawada]

Can you provide the sample video and program for this? It would be helpful to identify the root cause.

[Ian Wilson]

We used this code (see below)

vidObj = VideoReader('xylophone.mp4'); 
s = struct('cdata',zeros(vidObj.Height,vidObj.Width,3,'uint8'),...
  'colormap',[]);
vidObj.CurrentTime = 0.6;
k = 1;
while vidObj.CurrentTime <= 0.9
  s(k).cdata = readFrame(vidObj);
  k = k+1;
end

[Tohru Kikawada]

Thanks for providing this. I will take a look into this.

[Tohru Kikawada]

The code you shared works on my end. Could you please clarify the problem you are facing? Otherwise, it might be a problem depending on the codec which is installed on your end.

vidObj = VideoReader('xylophone.mp4');
s = struct('cdata',zeros(vidObj.Height,vidObj.Width,3,'uint8'),...
    'colormap',[]);
k = 1;
currAxes = axes;
while hasFrame(vidObj) 

      % Acquire the current time
      t = vidObj.CurrentTime;

      % Acquire the video frame
      vidFrame = readFrame(vidObj);

      % Needs Computer Vision System Toolbox
      vidFrame = insertText(vidFrame,[0 0],num2str(t,'time:% f'),'FontSize',40);

      % Capture the video frames at the specified duration
      if 0.6 <= t && t <= 0.9
          s(k).cdata = vidFrame;
          k = k+1;
      end

      % Show the video frame slowly
      image(vidFrame, 'Parent', currAxes);
      currAxes.Visible = 'off';
      drawnow limitrate;
      pause(1/vidObj.FrameRate);
  end

% Display the captured results
frames = cat(4,s.cdata);
figure, montage(frames);

[Anna Karchevskaya]

Good day, I used the same code on my video, but I have two questions:

1) Is it possible to reduce numer of frames? I want to get frames for every 150 ms for a specific period of time. I mean, I got the idea, how to do it:

https://www.mathworks.com/matlabcentral/answers/449426-how-do-i-save-every-nth-frame-of-a-video-and-save-these-images-to-a-folder-of-my-choosing

But I cant understand how to implement this code into your?

2) How can I export these frames one by one (for a specific period of time), so I won't get the "montage" - picture in the end. I mean, what should be written in the code in this case?

Thank you