How can sync a video to the plot?

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Sujan Ponnappa
Sujan Ponnappa 2020-1-9
回答： Swastik Sarkar 2025-6-20
I am trying to sync the video to the plot such that when the video plays(slicing a potato on a pressure sensor) the corresponding pressure signals are plotted.
But I am not able to sync the speed of the video to the speed of the plot.
I have also attached the video and the excel file of the pressure data to this .
Could anyone help me to solve this?
rng default
Fs = 24;
xs = potatoslicetimesync.Force;
ts = (0:length(xs)-1/Fs);
%plot(ts,xs)
%% Setup the subplots
ax1 = subplot(2,1,1); % For video
ax2 = subplot(2,1,2); % For pressure plot
%%% Setup VideoReader object
filename = 'slicesync.avi';
v = VideoReader(filename);
frameratevideo=v.FrameRate;
s = VideoWriter('C:\Users\Suj\Desktop\Master Thesis\Videos\slicesync.avi');
s.FrameRate = 500;
nFrames = v.Duration*v.FrameRate; % Number of frames
% Display the first frame in the top subplot
vidFrame = readFrame(v);
v.CurrentTime = 0;
image(vidFrame, 'Parent', ax1);
ax1.Visible = 'off';
%%% Load the pressure data
t = ts; % Cooked up for this example, use your actual data
y = xs;
nDataPoints = length(t); % Number of data points
step = round((nFrames/nDataPoints));
index = 1:0.55:nDataPoints;
i = 2;
% Diplay the plot corresponds to the first frame in the bottom subplot
h = plot(ax2,t(1:index(i)),y(1:index(i)),'-k');
% Fix the axes
ax2.XLim = [t(1) t(end)];
ax2.YLim = [min(y) max(y)];
%%% Animate
while hasFrame(v)
pause(1/v.FrameRate);
%pause(0.01)
vidFrame = readFrame(v);
image(vidFrame, 'Parent', ax1);
ax1.Visible = 'off';
i = i + 1;
set(h,'YData',y(1:index(i)), 'XData', t(1:index(i)))
end
%%% Load the pressure data
t = ts; % your actual data
y = xs;
nDataPoints = length(t); % Number of data points
step = round((nFrames/nDataPoints));
index = 1:step:nDataPoints;
i = 2;
% Diplay the plot corresponds to the first frame in the bottom subplot
h = plot(ax2,t(1:index(i)),y(1:index(i)),'-k');
% Fix the axes
ax2.XLim = [t(1) t(end)];
ax2.YLim = [min(y) max(y)];
%%% Animate
while hasFrame(v)
pause(1/s.FrameRate);
%pause(0.01)
vidFrame = readFrame(v);
image(vidFrame, 'Parent', ax1);
ax1.Visible = 'off';
i = i + 1;
set(h,'YData',y(1:index(i)), 'XData', t(1:index(i)))
end

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回答（1 个）

Swastik Sarkar
Swastik Sarkar 2025-6-20
Hi @Sujan Ponnappa,
There appear to be a few inconsistencies in the current implementation. The following adjustments may help improve synchronization between the video and the pressure plot:
Sampling time
In the section:
ts = (0:length(xs)-1/Fs);
This expression does not correctly compute the sampling time intervals. The division by Fs is applied only to the last element due to operator precedence. To generate a proper time vector corresponding to the sampling frequency, consider using:
ts = (0:length(xs)-1) / Fs;
Index Vector and Interpolation
In the section:
step = round((nFrames/nDataPoints));
index = 1:0.55:nDataPoints;
This approach may not ensure consistent alignment between the video frames and the pressure data. A more reliable method would be to interpolate the pressure values to match the number of video frames. This can be done as follows:
t_interp = linspace(ts(1), ts(end), nFrames);
xs_interp = interp1(ts, xs, t_interp, 'linear');
This ensures that each video frame corresponds to a pressure value, maintaining temporal consistency. Additional information on interp1 can be found in the MATLAB documentation.
https://www.mathworks.com/help/matlab/ref/double.interp1.html
Since the pressure data is now interpolated to match the video frame count, the two separate animation loops are no longer necessary. The logic can be consolidated into a single loop that updates both the video frame and the corresponding plot point-by-point.
Hope this helps synchronize the plots !

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