Adisorn - what is your order of operations? Do you launch the GUI and then call realtimefunction and pass in the handle to the GUI? Where is webcam3 defined or is this a function?
If you are trying to save the vid object to handles then you could do something like
function [] = realtimefunction(GuiHandle)
% your code
handles.vid = vid;
guidata(GuiHandle, handles);
which will update the handles structure of your GUI with the vid object. Then in your exit_Callback, you could do something like
function exit_Callback(hObject, eventdata, handles)
if isfield(handles, 'vid') && ~isempty(handles.vid)
delete(handles.vid); % or close, whatever is relevant
handles.vid = [];
guidata(hObject, handles)
end
As an aside, you should try to avoid using global variables.
