MATLAB Answers


"Preview Vid" doesn't work properly after compiling into standalone executable

Asked by James Sieracki on 20 Jan 2016
Latest activity Commented on by shlom41k on 20 Mar 2019
I have written a GUI to show four live video streams from HD webcams (Logitech C920). When I run my GUI in MATLAB, it functions flawlessly, press the "Preview" pushbutton and it detects if there are 1-4 cameras and displays their live images in axes in the GUI. After compiling to a standalone executable using the Compiler Application, when the "Preview" pushbutton is pressed, it shows 1 fewer cameras then the number selected, and it doesn't show a live stream, just a still of the first frame they see. The rest of the code seems to function properly (all cameras continue to record after I hit the "Begin" pushbutton. Below is the code for the "Preview" pushbutton (please disregard the sad nested if loop in the for loop, that was a bit of a workaround for an issue I was seeing earlier).
function Preview_Callback(hObject, ~, handles)
% hObject handle to Preview (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
handles.TLI = ceil(handles.expLengthMin/300); %Time between images (timelapse interval)
handles.fileName = [date,'_',handles.Manufacturer,'_',handles.Bandage];
for i=1:handles.numCamera
handles.vid(i) = videoinput('winvideo', i, 'RGB24_1920x1080'); %Video Format
handles.src(i) = getselectedsource(handles.vid(i));
handles.src(i).FrameRate = '5.0000'; %Frame rate
handles.src(i).FocusMode = 'manual'; %Focus mode
handles.src(i).Focus = 50;% Focus length for glass cylinder
handles.frameRate = str2double(handles.src(i).FrameRate);
handles.vid(i).FramesPerTrigger = handles.expLengthMin/handles.TLI;
handles.vid(i).FrameGrabInterval = (handles.frameRate*60)*handles.TLI;
handles.vid(i).LoggingMode = 'disk';
docname = [handles.fileName,'_#',num2str(i),'.avi'];
handles.diskLogger = VideoWriter(docname, 'Uncompressed AVI');
handles.diskLogger.FrameRate = 60/handles.TLI;
handles.vid(i).DiskLogger = handles.diskLogger;
vidRes = handles.vid(1).VideoResolution;
nBands = handles.vid(1).NumberOfBands;
for i=1:handles.numCamera
if i == 1;
h(1) = image(zeros(vidRes(2),vidRes(1),nBands),'Parent',handles.axes1);
elseif i == 2;
h(2) = image(zeros(vidRes(2),vidRes(1),nBands),'Parent',handles.axes2);
elseif i == 3;
h(3) = image(zeros(vidRes(2),vidRes(1),nBands),'Parent',handles.axes3);
elseif i == 4;
h(4) = image(zeros(vidRes(2),vidRes(1),nBands),'Parent',handles.axes4);


Is it always the same camera number that is affected, such as always the 4th one, even if you reorder the cameras? Or is it always the same camera that is affected (according to the detailed identification information) ?
No sir, neither. It is always just the last camera that my code calls for that doesn't show up. And it doesn't matter what the other cameras are that show up on the axes, they will just show the first frame snapshot. I've tried several different orders of the cameras and two separate computers.

Sign in to comment.

1 Answer

Answer by Harsheel
on 21 Jan 2016
 Accepted Answer

Seems like a bug to me. To work around the issue, make sure that the main function does not end before the whole application does; you can use the "waitfor" function to accomplish this.
For example if you have a GUIDE GUI myGUI, where somewhere in the callback of this GUI "preview" is actually called, and you used to compile myGUI into myGUI.exe you can work around the issue by writing the following function:
function myMain
Use myMain.m as the main function for your standalone.


Holy ****. This solved the issue. I didn't edit the master code at all, I just wrote this up and compiled it and it works, thank you!
Instead of creating a wrapper, I just put
(which appears commented out right after opening function when using Guide) and it worked. waitfor didn't work for me. But this has created another problem: the toolbar buttons like zoom don't work.
Thank you so much! It worked:
function myMain

Sign in to comment.