Stopping showing a MP4 file (frame) by exit button

Question

Jason 2023-1-30

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1903350-stopping-showing-a-mp4-file-frame-by-exit-button

评论： Image Analyst 2023-1-30

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

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Answer 1

Image Analyst 2023-1-30

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1903350-stopping-showing-a-mp4-file-frame-by-exit-button#answer_1159710

在 MATLAB Online 中打开

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;

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Jason 2023-1-30

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 2023-1-30

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.

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