Play, Pause, Rewind, and Fast Forward Buttons (App Designer)

I am using the app designer and was wondering about implementing Play, Pause, Rewind, and Fast Forward buttons. Right now I do not have these features implemented - I just have a video playing using a combination of VideoReader, hasFrame, readFrame, and imshow functions. Here is my code:

          filename = vidfile;
          v = VideoReader(filename);
          frame = 0;
          app.OffsetFrameNumberEditField.Value = offsets(index);
          ix = 1;
          x = 1;
          while hasFrame(v)
              frame = frame + 1;
              app.AbsoluteFrameNumberEditField.Value = frame;
              app.OffsetFrameNumberEditField.Value = frame+offsets(index);
              if frame == 1
                  cla(app.Video)
                  fig = imshow(readFrame(v), 'Parent', app.Video);

              else
                  set(fig,'CData',readFrame(v))
              end
                if ge(frame,range(1)) &&  le(frame,range(end))
                    if x == 1
                        SP = scatter(app.SagittalAxes,dataS(ix,1), dataS(ix,4),'MarkerFaceColor','k','MarkerEdgeColor','k');
                        FP = scatter(app.FrontalAxes,dataF(ix,1), dataF(ix,4),'MarkerFaceColor','k','MarkerEdgeColor','k');
                        TP = scatter(app.TransverseAxes,dataT(ix,1), dataT(ix,4),'MarkerFaceColor','k','MarkerEdgeColor','k');
                        x = x+1;
                    else
                        set(SP,'XData',dataS(ix,1))
                        set(SP,'YData',dataS(ix,4))
                        set(FP,'XData',dataF(ix,1))
                        set(FP,'YData',dataF(ix,4))
                        set(TP,'XData',dataT(ix,1))
                        set(TP,'YData',dataT(ix,4))
                    end
                    ix = ix+1;
                end
                pause(0.005)
            end

Answer 1

[Kevin Chng]

Hi, your question is really interesting. You may consider my solution as follows

It is including play, pause, resume,speed up,slow down, forward and rewind/backward.

button :

function play(app,event)
global numFrames pauseS stop speed iter
pauseS=true
stop = true
speed = 1

% Count the number of frames
  numFrames = 1;
  v = VideoReader('song.mp4')
  while hasFrame(v)
        readFrame(v)
        numFrames = numFrames +1;
end

v= VideoReader('song.mp4)
iter=1;

while(1)
   frame = read(v,iter)
   imshow(frame,'Parent',app.UIAxes'); % You may use button to host the image
   drawnow

     % here for slow down and speed up
     if speed ==1
     elseif speed==2
          pause(0.0001);
    elseif speed ==3
       pause(0.1)
    elseif spped==4
         pause(1)
    end

    % Here for pause and resume
    if pauseS == false
        while(1)
        pause(0.001);
        if pauseS == true
        break;
        end
        end
    end

    % Stop playing
    if stop == false
       break;
    end

    iter = iter+1;

    % If frame is finished, break
    if iter>numFrames
         break;
    end

    end

Pause Button :

function pause(app, event)
    global pauseS
    if pauseS==true
         pauseS=false;
    else
         pauseS=true;
    end

end

Stop Button :

function stop(app, event)
      global stop
     stop=false;
  end

Speed Up and Slow Down Button :

function speedup(app,event)
    global speed
    if speed==2
       speed=1;
    elseif speed ==3
       speed=2;
    elseif speed ==4
       speed=3;
    end
end

function slowdown(app,event)
  global speed
 if speed ==1
     speed=2;
 elseif speed==2
    speed=3;
 elseif speed==3
    speed=4;
 end
end

forward and rewind button :

function forward(app,event)
       global iter numFrames
       if iter<(numFrames-100)
       iter = iter +100;
       end
end

function rewind(app,event)

      global iter
      if iter>100
          iter=iter-100;
      end
    end

Let me know if you have any question. Kindly accept my answer if it is working for you.

[Ledoux Laboratory]

Thanks! It looks like we're working on very similar apps. I'm working on modifying my code but I'm wondering if I'm structuring it correctly based on your code:

            %%Show first video frame before you hit play button

            [Strains,offsets] = kinematicsStrain(app,Subject,Condition);
            index = str2double(trial);

            app.OffsetFrameEditField.Value = offsets(index);

            global numFrames pauseS stop speed iter frame ix x filename range offset fig
            range = (Strains(index,1)-offsets(index)):(Strains(index,2)-offsets(index));
            pauseS=true;
            stop = true;
            speed = 1;
            frame = 0;
            ix = 1;
            x = 1;

            filename = vidfile;
            v = VideoReader(filename);
            numFrames = 1;

            while hasFrame(v)
                readFrame(v);
                numFrames = numFrames + 1;
            end

            v = VideoReader(filename);
            iter = 1;
            offset = offsets(index);
            info = get(v);
            v.CurrentTime=(iter-1)/info.FrameRate;

            app.AbsFrameEditField.Value = frame;
            app.OffsetFrameEditField.Value = frame+offset;
            cla(app.Video)
            frameData = readFrame(v);
            fig = imshow(frameData, 'Parent', app.Video);
            drawnow

Play button

global numFrames pauseS stop speed iter frame ix x filename range offset fig

            v= VideoReader(filename);
            iter=1;

            while(1)
                app.AbsFrameEditField.Value = frame;
                app.OffsetFrameEditField.Value = frame+offset;

                info = get(v);
                v.CurrentTime=(iter-1)/info.FrameRate;
                frameData = readFrame(v);
                set(fig,'CData',frameData)

                if ge(frame,range(1)) &&  le(frame,range(end))
                    if x == 1
                        SP = scatter(app.SagittalAxes,dataS(ix,1), dataS(ix,4),'MarkerFaceColor','k','MarkerEdgeColor','k');
                        FP = scatter(app.FrontalAxes,dataF(ix,1), dataF(ix,4),'MarkerFaceColor','k','MarkerEdgeColor','k');
                        TP = scatter(app.TransverseAxes,dataT(ix,1), dataT(ix,4),'MarkerFaceColor','k','MarkerEdgeColor','k');
                        x = x+1;
                    else
                        set(SP,'XData',dataS(ix,1))
                        set(SP,'YData',dataS(ix,4))
                        set(FP,'XData',dataF(ix,1))
                        set(FP,'YData',dataF(ix,4))
                        set(TP,'XData',dataT(ix,1))
                        set(TP,'YData',dataT(ix,4))
                    end
                    ix = ix+1;
                    frame = frame+1;
                end

                % here for slow down and speed up
                if speed ==1
                elseif speed==2
                    pause(0.0001);
                elseif speed ==3
                    pause(0.1)
                elseif spped==4
                    pause(1)
                end
                % Here for pause and resume
                if pauseS == false
                    while(1)
                        pause(0.001);
                        if pauseS == true
                            break;
                        end
                    end
                end
                % Stop playing
                if stop == false
                    break;
                end
                iter = iter+1;

                % If frame is finished, break
                if iter>numFrames
                    break;
                end
            end
            hold(app.SagittalAxes,'off')
            hold(app.FrontalAxes,'off')
            hold(app.TransverseAxes,'off')

The other buttons are coded identically to yours. The problem I have is that the first video frame is not being read. Then when I hit the play button I run into an error that says that the object is invalid or deleted, probably due to the video not existing at startup. Anything you can see that might be causing this?

Also for clarification, are you using a state button for your pause/resume functions?

[Kevin Chng]

Hi,

For displaying first frame, you might try to edit your code as follows:

frameData = read(v,1);

put 1 at the back.

I use normal button. Then click the callback function.

Why is there an error when you hit your button?

I'm not sure about this part. However, in my code, there is iter behind the v.

 frameData = read(v,iter);
 set(fig,'CData',frameData)

Why do you set your frame(Image) to fig? not app.Video?

[Umair Mughal]

The best solution of stop is to use globals... Thanks..

[Jesper Ankersen]

Are you using the regular button or state button for this application ?