How to write a video file with analog plots?

Question

horizon 2019-5-1

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/459534-how-to-write-a-video-file-with-analog-plots

评论： horizon 2019-5-6

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

2 个评论
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Walter Roberson 2019-5-1

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 2019-5-4

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?

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Answer 1

Walter Roberson 2019-5-4

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/459534-how-to-write-a-video-file-with-analog-plots#answer_373541

在 MATLAB Online 中打开

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