Stopping showing a MP4 file (frame) by exit button

Hello,I am reading a mp4 video and have created a figure with the axes, and two buttons. My two buttons for play and exit have the following callbacks associated to them:

 function exitCallback(app, source, eventargs,videoSrc,hFig)    
            % Close the video file
            %release(videoSrc); This doesn't work, so try using delete
            delete(videoSrc);
            % Close the figure window
            close(hFig);
        end

 function playCallback(app, source, eventargs,v,hAxis)    
             try                
                dur=v.Duration;
                axes(hAxis);
                while(hasFrame(v))
                    frame = readFrame(v);                
                    imshow(frame); %colormap(jet)
                    title(sprintf('Current Time = %.3f sec    (%.3f)', v.CurrentTime,dur),'Color', 'r');
                    pause(2/v.FrameRate);
                end
             catch
             end  
 end

The playback works find and also the exitcallback sort of works. It does stop the video and delete the videoSrc (v) but it then causes the while loop in the playcall back to throw an error. Is there a way so stop the playing without causing an error. I was looking for a stopreadingframe(v) sort of function, but it doesn't exist.

For info, here's the main part of my code.

            % Get File
           try
                [file,folder]=uigetfile({'*.mp4','MP4 Files'},'Open video',app.VideoSaveDirEditField.Value);
           catch
                [file,folder]=uigetfile({'*.mp4','MP4 Files'},'Open video','C:\');
           end 
            
            filename=fullfile(folder,file);
            v = VideoReader(filename);
            %Get info from video
            D=['Duration(s): ',num2str(v.Duration,'%.2f')];
            B=['BitsperPixel: ',num2str(v.BitsPerPixel)];
            F=['FrameRate: ',num2str(v.FrameRate)];
            N=['Num Frames: ',num2str(v.NumFrames)];
            mstr=({D;F;B;N});                     % Use braces       
            f = msgbox(mstr,'icon','help');       % strcat is not necessary. The straight and complete answer is the use of {} instead of [ ] to have the messaeg in the msgbox.  
            waitforbuttonpress;
           

            %v.Colormap = jet
            ReportMessage(app,['Opened Video ',file]);
            numFrames=v.NumFrames; 
            ReportMessage(app,['...Num Frames: ',num2str(numFrames)]);
            fRate=v.FrameRate;
            ReportMessage(app,['...FrameRate: ',num2str(fRate)]);
            dur=v.Duration;
            
            f1=figure('Name', 'MP4 Preview Window', 'Units','normalized',...
            'Position',[0.3 0.4 0.5 0.5]);

%             uicontrol('String', 'Close', 'Callback', {@app.exitCallback,v,f1});    % uicontrol('String', 'Close', 'Callback', 'close(gcf)');


            pos=[0 0 1 1];
            hPanel = uipanel('parent',f1,'Position',pos,'Units','Normalized');
            % Create axis
            hAxis = axes('position',[0.1 0.1 0.8 0.85],'Parent',hPanel);
            hAxis.XTick = []; hAxis.YTick = [];        
            hAxis.XColor = [1 1 1];   hAxis.YColor = [1 1 1];

            % Play button with text Start/Pause/Continue
             uicontrol(f1,'Units', 'pixels','Style','pushbutton','String','Start',...
                'Position',[20 10 100 40], 'Callback', {@app.playCallback,v,hAxis});

             % Play button with text STOP
             uicontrol(f1,'Units', 'pixels','Style','pushbutton','String','Stop',...
                'Position',[130 10 100 40], 'Callback', {@app.exitCallback,v,f1});
           %display first frame   
           frame1 = readFrame(v);
           axes(hAxis);
           imshow(frame1);

Thanks for any help

Jason

Answer 1

[Image Analyst]

You could make a checkbox on the window called chkFinishNow and then check it in your loop

app.chkFinishNow.Value = false;
while(hasFrame(v)) & ~app.chkFinishNow.Value % Continues as long as the checkbox is not checked.
    frame = readFrame(v);                
    imshow(frame); %colormap(jet)
    title(sprintf('Current Time = %.3f sec    (%.3f)', v.CurrentTime,dur),'Color', 'r');
    pause(2/v.FrameRate);
end
% Make sure it's turned off again.
app.chkFinishNow.Value = false;

[Jason]

perfect, thankyou!

[Jason]

This seems to work

c=uicontrol(f1,'Units', 'pixels','Style','checkbox','String','PauseNow',...
                'Position',[240 10 100 40]);
              c.Value = false;   
app.chkFinishNow=c;   %(make it accessible to other methods)              

But it doesn't stop very quick, takes about 2s to stop. Is there away to have the checkbox click effect quicker?

[Jason]

update:

according to the link below, drawnow is used to access the interupt queue

https://uk.mathworks.com/matlabcentral/answers/100558-how-do-i-set-up-a-uicontrol-callback-to-interrupt-a-routine

So the full playcallback is:

pp.chkFinishNow.Value = false;
while(hasFrame(v)) & ~app.chkFinishNow.Value % Continues as long as the checkbox is not checked.
    frame = readFrame(v);                
    imshow(frame); %colormap(jet)
    title(sprintf('Current Time = %.3f sec    (%.3f)', v.CurrentTime,dur),'Color', 'r');
    pause(2/v.FrameRate); drawnow
end
% Make sure it's turned off again.
app.chkFinishNow.Value = false;

[Image Analyst]

Well you have a pause() there so it will only get back up to the top to check after the pause has finished. If you want you can put the check for the checkbox value in lots of places:

app.chkFinishNow.Value = false;
while(hasFrame(v)) & ~app.chkFinishNow.Value % Continues as long as the checkbox is not checked.
    frame = readFrame(v);                
    imshow(frame); %colormap(jet)
    title(sprintf('Current Time = %.3f sec    (%.3f)', v.CurrentTime,dur),'Color', 'r');
    drawnow;
    if app.chkFinishNow.Value % Check if user checked the box.
        break; % Bail out of the while loop.
    end
    % More code...
    if app.chkFinishNow.Value % Check if user checked the box.
        break; % Bail out of the while loop.
    end
    % More code...
    if app.chkFinishNow.Value % Check if user checked the box.
        break; % Bail out of the while loop.
    end
    pause(2/v.FrameRate); 
    drawnow
end
% Make sure it's turned off again.
app.chkFinishNow.Value = false;

[Jason]

Thanks I.A, ill give that suggestion a go. Although without the drawnow, after pressing the checkbox, the loop carried on many many times, not just once. The FrameRate is about 20 fps, so the pause is 2/20 s, so small.

[Image Analyst]

Maybe it's just in such an intensive loop that it doesn't get around to checking the checkbox for a while. I think though that a drawnow or pause would let it stop for air enough to go and check other OS messages (like the box was checked). If the timing is that critical you may have to look for other ways to break out of the loop.