How to write a video file with analog plots?

I would like to write a graph to a video file.

It was succeeded to make a video to recode a graph with the following simple code, but I have no idea how this program is applicable to my program.

Though I tried to edit my code to recode plotting data for ten seconds of video, the file size of the video was 0 KB.

How should I fix my code?

Simple Code to create a video file from a graph

x = 0:100;
y = sin(x);

writerObj = VideoWriter('test.avi');
open(writerObj);

fig = plot(x,y);
set(fig, 'XDataSource', 'x');
set(fig, 'YDataSource', 'y');
set(gca, 'Xlim', [0 100], 'Ylim', [-20 20]);
set(gca,'nextplot','replacechildren');

for k = 0:20
    y = k*sin(x);
    refreshdata(fig);

    frame = getframe(gcf);
    writeVideo(writerObj, frame);
end

close(writerObj);

My Code

writerObj = VideoWriter('graph.avi');
open(writerObj);

tx = daq.createSession('ni');
s = daq.createSession('ni');

s.Rate = 400000;
ultraFreq = 40000;
numCycle =8

y = [y zeros(1,numCycle*s.Rate/ultraFreq)];
addAnalogOutputChannel(tx, 'Dev1', 'ao0', 'Voltage');
th=addlistener(tx, 'DataRequired', @queueMoreData);
addAnalogInputChannel(s,'Dev1', 'ai0', 'Voltage'); 
ch = addAnalogInputChannel(s, 'Dev1', 'ai1', 'Voltage'); 

h = addlistener(s, 'DataAvailable', @plotData); 
s.DurationInSeconds(1);
queueOutputData(tx, y');
startBackground(s);
tx.startForeground();


function plotData(src, event)
  t1 = event.TimeStamps(:,1);
  s1 = event.Data(:,1);
  s2 = event.Data(:,2);
  subplot(2,1,1)
  plot(t1,s1)
  ylim([-10.0 10.0]);
  title('s_1')
  
  subplot(2,1,2)
  plot(t1,s2)
  ylim([-10.0 10.0]);
  title('s_2')
  xlabel('Time (s)')

  while(10)
    frame = getframe(gcf);
    writeVideo(writerObj, frame)

end

function queueMoreData(src, event)
  queueOutputData(tx, y');
end

[Walter Roberson]

while(10) is an infinite loop. You would have to abort to get out of it, and that would leave the video unfinished.

writerObj is not within scope of function plotData. Easiest would probably be to use nested functions.

[horizon]

Thank you for your comment.

Why writerObj is not a global variable in this case?

It is defined before calling the function and how can I pass it to the function? Using a .mat file or redefine writerObj inside of the function?

Answer 1

[Walter Roberson]

function plot_session

    recording_time = 300;    %seconds
    
    ax1 = subplot(2,1,1);
    L1 = animatedline(ax1);
    ylim(ax1, [-10.0 10.0]);
    title(ax1, 's_1')
    xlabel(ax1, 'Time (s)')
    
    ax2 = subplot(2,1,2);
    L2 = animatedline(ax2);
    ylim(ax2, [-10 10.0]);
    title(ax2, 's_2')
    xlabel(ax2, 'Time (s)')
    
    writerObj = VideoWriter('graph.avi');
    open(writerObj);
    
    tx = daq.createSession('ni');
    s = daq.createSession('ni');
    s.Rate = 400000;
    ultraFreq = 40000;
    numCycle = 8;
    
    y = [y zeros(1,numCycle*s.Rate/ultraFreq)];
    addAnalogOutputChannel(tx, 'Dev1', 'ao0', 'Voltage');
    th = addlistener(tx, 'DataRequired', @queueMoreData);
    addAnalogInputChannel(s,'Dev1', 'ai0', 'Voltage'); 
    ch = addAnalogInputChannel(s, 'Dev1', 'ai1', 'Voltage'); 
    h = addlistener(s, 'DataAvailable', @plotData); 
    s.DurationInSeconds(1);
    queueOutputData(tx, y');
    
    startBackground(s);
    tx.startForeground();
    
    pause(recording_time)
    
    %cleanup time
    delete(th)
    delete(h)
    pause(1);   %time for last plot event
    close(writerObj);
    delete(s)
    delete(tx)
    
    function plotData(src, event)
      t1 = event.TimeStamps(:,1);
      s1 = event.Data(:,1);
      s2 = event.Data(:,2);
      addpoints(L1, t1, s1);
      addpoints(L2, t1, s2);
      drawnow();
      pause(0.05);  %in practice need time to render

      frame = getframe(gcf);
      writeVideo(writerObj, frame)
    end
    
    function queueMoreData(src, event)
      queueOutputData(tx, y');
    end
end

[horizon]

Thank you for your answer.

Does this answer is related to the following another question?

I have trouble with understanding how to use and the applicable cases of pause function on MATLAB.

How can I control the repeat analog output on MATLAB?

I would appreciate if you could help me again.