How do I export an animated figure to some video format for use in a presentation?

With code adapted from other help threads, I have an animated figure which plays a video (about 20 sec) in one subplot while simultaneously plotting associated data in the next subplot. I run the code in Live editor (and just normally, for that matter) and the figure works perfectly.

How do I get this animated figure into a video file of some kind for use in a presentation? (code below)

Incidentally, the live editor includes a small export button at the bottom right of the figure, but this seems to freeze the code and I only get a blank gray section when I click it. (pics)

%setup subplots
ax1 = subplot(2,1,1); % For video
ax2 = subplot(2,1,2); % For data plot

%setup videoreader object
CH47Landing = 'D:\Manual Backup\PROJECTS\Ice\Engineer Lake\Landing.mp4';
v = VideoReader(CH47Landing);
nFrames = v.Duration*v.FrameRate; % Number of frames
% Display the first frame in the top subplot
vidFrame = readFrame(v);
image(vidFrame, 'Parent', ax1);
ax1.Visible = 'off';
%Load Data
lt = TIMESTAMP; %use your actual data
y = ld5;
nDataPoints = length(lt); % Number of data points
step = 0.033; % Increase this value to get a higher plot rate
index = 1:step:nDataPoints;
i = 2;
% Diplay the plot corresponds to the first frame in the bottom subplot
h = plot(ax2,lt(1:floor(index(i))),y(1:floor(index(i))),'-k');
%Fix the Axes

ax2.XLim = [lt(1) lt(end)];
ax2.YLim = [min(y) max(y)];
%Animate
while hasFrame(v)
    pause(1/v.FrameRate);
    
    vidFrame = readFrame(v);
    image(vidFrame, 'Parent', ax1);
    ax1.Visible = 'off';
    
    i = i + 1;
    set(h,'YData',y(1:floor(index(i))), 'XData', lt(1:floor(index(i))))


subplot(2,1,1)
xlim([1 1921])
ylim([1 925])
subplot(2,1,2)
set(gca, 'YDir','reverse')
ylabel('Deflection (mm)')
xticklabels({'12:02:00 PPM','12:02:15 PM','12:02:29PM'})
title('CH47; 31Jan23; h(i)=70cm; AirT=18°F. PT=#5')
xlim([datetime(2023,2,16,12,2,0)...
      datetime(2023,2,16,12,2,40)])
ylim([0 15])
end

Answer 1

[Kevin Holly]

Daniel,

Please see the files attached and the code below. Saving the video should be faster when the figure's "Visible" property is set to "off" and when running it on a .m script instead of the Live Script.

Setup Figure

figure("Visible","off")
tiledlayout(2,1)
%setup subplots
ax1 = nexttile; % For video
ax2 = nexttile; % For data plot
%setup videoreader object
CH47Landing = 'xylophone.mp4';
v = VideoReader(CH47Landing);
nFrames = v.Duration*v.FrameRate; % Number of frames
% Display the first frame in the top subplot
vidFrame = readFrame(v);
image(vidFrame, 'Parent', ax1);
ax1.Visible = 'off';
%Load Data
lt = seconds(v.CurrentTime:1/v.FrameRate:v.NumFrames/v.FrameRate); %Note, this video is in seconds, so datetime was not used
y = rand(v.NumFrames,1)*15;
nDataPoints = length(lt); % Number of data points
step = 0.033; % Increase this value to get a higher plot rate
index = 1:step:nDataPoints;
ii = 2;
% Diplay the plot corresponds to the first frame in the bottom subplot
h = plot(ax2,lt(1:floor(index(ii))),y(1:floor(index(ii))),'-k');
%Fix the Axes
ax2.XLim = [lt(1) lt(end)];

set(gca, 'YDir','reverse')
ylim(ax2,[0 15])
title('CH47; 31Jan23; h(i)=70cm; AirT=18°F. PT=#5')
ylabel(ax1,'Deflection (mm)')

Save one frame at a time

vsave = VideoWriter('SavedFilebyFrame','MPEG-4');
h = plot(ax2,lt(1:floor(index(ii))),y(1:floor(index(ii))),'-k');
% lt = datetime(lt,'ConvertFrom','datenum','Format','HH:mm:ss.SSS');

open(vsave)
%Animate
while hasFrame(v)
    vidFrame = readFrame(v);
    image(vidFrame, 'Parent', ax1);
    ax1.Visible = 'off';
    ii = ii + 1;
    set(h,'YData',y(1:floor(index(ii))), 'XData', lt(1:floor(index(ii))))
    xlim(ax2,[0 max(h.XData)])
    ylabel(ax1,'Deflection (mm)')
    img = getframe(gcf);
    writeVideo(vsave,img.cdata)
end
close(vsave)

Save entire video at once

Create 4D matrix of video

ii=0;
v = VideoReader(CH47Landing);
lt = 1/v.FrameRate:1/v.FrameRate:v.NumFrames*v.FrameRate;
while hasFrame(v)
    ii = ii + 1;
    vidFrame(:,:,:,ii) = readFrame(v);
end

Write video

figure("Visible","off")
vsave = VideoWriter('SavedFile','MPEG-4');
h = plot(ax2,lt(1:floor(index(ii))),y(1:floor(index(ii))),'-k');
% lt = datetime(lt','ConvertFrom','datenum','Format','HH:mm:ss.SSS');

open(vsave)
for ii = 1:v.NumFrames
%     pause(1/v.FrameRate);
    image(vidFrame(:,:,:,ii), 'Parent', ax1);
    ax1.Visible = 'off';
    set(h,'YData',y(1:floor(index(ii))), 'XData', lt(1:floor(index(ii))))
    xlim(ax2,[0 max(h.XData)])
    img = getframe(gcf);
    writeVideo(vsave,img.cdata);
end
close(vsave)

Answer 2

[Anton Kogios]

Documentation for recording animations: https://mathworks.com/help/matlab/creating_plots/record-animation-for-playback.html

and exporting animations: https://mathworks.com/help/symbolic/writeanimation.html

In your while loop, at the end add

vid(i) = getframe(gcf);

and then at the end of the script add

v = VideoWriter('recordedAnimation,'MPEG-4');

open(v)
for i = 1:length(vid)
    writeVideo(v,vid(i))
end
close(v)

You may have to modify the above code since I cannot test it given you haven't provided the Landing.mp4 video. There is plenty of helpful documention if you search this topic up on Google. This may also help: https://mathworks.com/matlabcentral/answers/455886-how-to-save-animated-plots

[Daniel]

Unfortunately, this code did not work.

I'm getting "Error using VideoWriter/WriteVideo The 'cdata' field of FRAME must not be empty"

I would share the video, but it is controlled unfortunately.

[Anton Kogios]

Sorry I should have mentioned that you need to initialise vid:

vid(1:n) = struct('cdata',zeros(420,560,3,'uint8'),'colormap',[]);

n is the number of frames, and 420 and 560 is the size/resolution of your figure window.

[Daniel]

Pardon my inexperience with creating videos from MATLAB, I'm getting another error

ax1 = subplot(2,1,1); % For video
ax2 = subplot(2,1,2); % For data plot

%setup videoreader object
CH47Landing = 'D:\Manual Backup\PROJECTS\Ice\Engineer Lake\Landing.mp4';
v = VideoReader(CH47Landing);
nFrames = v.Duration*v.FrameRate; % Number of frames
% Display the first frame in the top subplot
vidFrame = readFrame(v);
image(vidFrame, 'Parent', ax1);
ax1.Visible = 'off';
%Load Data
lt = TIMESTAMP; %use your actual data
y = Ld5;
nDataPoints = length(lt); % Number of data points
step = 0.033; % Increase this value to get a higher plot rate
index = 1:step:nDataPoints;
i = 2;
% Diplay the plot corresponds to the first frame in the bottom subplot
h = plot(ax2,lt(1:floor(index(i))),y(1:floor(index(i))),'-k');
%Fix the Axes

ax2.XLim = [lt(1) lt(end)];
ax2.YLim = [min(y) max(y)];
%Animate

while hasFrame(v)
    pause(1/v.FrameRate);
    
    vidFrame = readFrame(v);
    image(vidFrame, 'Parent', ax1);
    ax1.Visible = 'off';
    
    i = i + 1;
    vid(i) = getframe(gcf);


set(h,'YData',y(1:floor(index(i))), 'XData', lt(1:floor(index(i))))
subplot(2,1,1)
xlim([1 1921])
ylim([1 925])
subplot(2,1,2)
set(gca, 'YDir','reverse')
ylabel('Deflection (mm)')
xticklabels({'12:02:00 PPM','12:02:15 PM','12:02:29PM'})
title('CH47; 31Jan23; h(i)=70cm; AirT=18°F. PT=#5')
xlim([datetime(2023,2,16,12,2,0)...
      datetime(2023,2,16,12,2,40)])
ylim([0 15])

vid(1:990) = struct('cdata',zeros(420,560,3,'uint8'),'colormap',[]);
v = VideoWriter('recordedAnimation','MPEG-4');

open(v)
for i = 1:length(vid)
    writeVideo(v,vid(i))
end
close(v)
end

[Daniel]

I realized v already existed as VideoReader, so I renamed to v1 and now the script is running but it does not stop... Just says that that script is running.. has been going on now for 5 minutes so I stopped it because it shouldn't take that long.

[Anton Kogios]

Instead of a while loop, read the number of frames in the video and set up a for loop. Something like:

for j = 1:nFrames
    ...
end

[Daniel]

Ok looks like this outputs the Matlab figure which plays the video, but then it does not plot the data or output a video file.

[Anton Kogios]

This should be at the very end, outside the for loop (the while loop in your code above):

v = VideoWriter('recordedAnimation','MPEG-4');

open(v)
for i = 1:length(vid)
    writeVideo(v,vid(i))
end
close(v)

And this should be before the for loop (the while loop in your code above):

vid(1:990) = struct('cdata',zeros(420,560,3,'uint8'),'colormap',[]);

It may be best if you start with a simple example first and get that to work. You should also read the documentation I mentioned in my first answer so you know what the code is actually doing, rather than copy-pasting what I say at the incorrect locations.

Answer 3

[Simon Chan]

If you accept an animated GIF file as the output, check this link:

https://www.mathworks.com/matlabcentral/answers/94495-how-can-i-create-animated-gif-images-in-matlab

[Daniel]

I would definitely be fine with that option. The difficulty I think is that there is a video in the script already, and I am not sure how to handle that. If it were a simple matter of animating a plotting function or something, it might be easier, but I need this video in the output as well.