Recording video from three webcams with app designer

Hi All,

Posting again with more tags.

I am trying to create a simple MatLab app using the app designer. I have three USB webcams (named ANT, POST and MED) plugged into my laptop which have a resolution of 1080 x1920. The goal is to press a record button so a 5 second video records simultaneously from each camera at at least 25 fps.

I have posted the app and the 'push record button' callback code below:

I find the videos record and save to the current folder, however, the playback speed and duration of the videos is really variable and usually not 5 seconds.

Sometimes MatLab crashes and sends an error message that there is insufficient physical memory. My laptop has 16GB of RAM, however, having matlab open as well as running the app does use a lot.

I have tried packaging the app so it is a standalone .exe to use less RAM, however, this doesnt seem to work. Is this because without MatLab open, the app does not have a folder to store the output videos in? If so, how can I tell a standalone app to save files to a specific folder? would I have to add a browse folder box?

Also is the code incorrect? Do I need to set the individual properties of each video object? Or can a loop be used to make the code more succinct?

Any help much appreciated.

Many thanks.

The app looks like this:

My code for the properties and the record button pushed callback is:

properties (Access = private)
    AntCam = videoinput('winvideo',2); % Description 
    PostCam = videoinput('winvideo',3); % Description
    MedCam = videoinput('winvideo',4); % Description
    Filename;
    Date;
    Sample;
end
% Button pushed function: RECORDButton
        function RECORDButtonPushed(app, event)
            
        %% Set Properties for Videoinput AntCam
        app.AntCam.TimeOut = Inf;
        app.AntCam.FrameGrabInterval = 1;
        app.AntCam.LoggingMode = 'disk&memory';
        app.AntCam.FramesPerTrigger = 1;
        app.AntCam.TriggerRepeat = Inf;
        app.AntCam.TimerPeriod = 5;
        
        %% Set Properties for Videoinput PostCam
        app.PostCam.TimeOut = Inf;
        app.PostCam.FrameGrabInterval = 1;
        app.PostCam.LoggingMode = 'disk&memory';
        app.PostCam.FramesPerTrigger = 1;
        app.PostCam.TriggerRepeat = Inf;
        app.PostCam.TimerPeriod = 5;
        
        %% Set Properties for Videoinput MedCam
        app.MedCam.TimeOut = Inf;
        app.MedCam.FrameGrabInterval = 1;
        app.MedCam.LoggingMode = 'disk&memory';
        app.MedCam.FramesPerTrigger = 1;
        app.MedCam.TriggerRepeat = Inf;
        app.MedCam.TimerPeriod = 5;
        
        %% Construct VideoWriter objects and set Disk Logger Properties    
        vidWriterAnt = VideoWriter(([app.Date, app.Sample, app.Filename, 'ANT']),'MPEG-4');
        vidWriterPost = VideoWriter(([app.Date, app.Sample, app.Filename,'POST']),'MPEG-4');
        vidWriterMed = VideoWriter(([app.Date, app.Sample, app.Filename, 'MED']),'MPEG-4');
       
        vidWriterAnt.Quality = 50;
        vidWriterAnt.FrameRate = 25;
        app.AntCam.DiskLogger = vidWriterAnt;
        
        vidWriterPost.Quality = 50;
        vidWriterPost.FrameRate = 25;
        app.PostCam.DiskLogger = vidWriterPost;
        
        vidWriterMed.Quality = 50;
        vidWriterMed.FrameRate = 25;
        app.MedCam.DiskLogger = vidWriterMed;
        
        start(app.AntCam);
        start(app.PostCam);
        start(app.MedCam);
        app.AntCam.TimerFcn = {'stop'};
        app.PostCam.TimerFcn = {'stop'};
        app.MedCam.TimerFcn = {'stop'};
        
        clear app.AntCam
        clear app.PostCam
        clear app.MedCam
        end
        

[Geoff Hayes]

Genevieve - have you tried just using one webcam to see what happens? If that works, then you could add the second and then (later) the third web cam once the first two are working.

I do see that you add your timer function callbacks AFTER you call start on the video objects. Depending upon whether start is blocking or not, these callbacks may not be assigned properly and so the video acquisition will never end (maybe the reason for the out of memory?). Try just using this code (which is a subset of yours):

% Button pushed function: RECORDButton
function RECORDButtonPushed(app, event)
    
    %% Set Properties for Videoinput AntCam
    app.AntCam.TimeOut = Inf;
    app.AntCam.FrameGrabInterval = 1;
    app.AntCam.LoggingMode = 'disk&memory';
    app.AntCam.FramesPerTrigger = 1;
    app.AntCam.TriggerRepeat = Inf;
    app.AntCam.TimerPeriod = 5;
    app.AntCam.TimerFcn = {'stop'};  % <--- do this here before call to start
    
    %% Construct VideoWriter objects and set Disk Logger Properties    
    vidWriterAnt = VideoWriter(([app.Date, app.Sample, app.Filename, 'ANT']),'MPEG-4');
    vidWriterAnt.Quality = 50;
    vidWriterAnt.FrameRate = 25;
    app.AntCam.DiskLogger = vidWriterAnt;
    
    start(app.AntCam);
    
    % clear app.AntCam  <---- Is this necessary?
    end

I don't have the appropriate toolbox to test the above out, but perhaps it will help in some way.

[Genevieve Pounds]

Hi Geoff,

Thankyou for your comment.

I tried the first camera with the code you posted above and it worked fine, thankyou.

I then added the second camera and the code ran, however, the second camera video filmed for 7 seconds rather than 5 seconds. In addition, the trigger for the two cameras was not simultaneous. It seems the first camera always triggers slightly before the second.

When adding the third camera, videos were logged from each device, however, MatLab crash reporter popped up after running the app and closed MatLab. Sometimes the videos from the second and third cameras recorded for ~20 seconds. However, the video for the first camera was around 5 seconds. The triggers were also slightly out of sync.

I found that running the code as a script rather than a MatLab app meant that MatLab did not crash but the same issues with video time/sync occured.

Is it possible that the cameras are struggling to reach the set framerate, therefore, the time of the video is being extended and the TimerFcn is being ignored, to compensate for that?

Many thanks,

Answer 1

[Tatiana Leon]

hi

I have a mistake

Undefined function 'videoinput' for input arguments of type 'char'.

Can somebody help me